Division of Agricultural Scienc e s ^^Q UNIVERSITY OF CALIFORNI FERTILIZATION of IRRIGATED PASTURE and FORAGE CROPS in California :AI - vllA AGRICULTURAL EX RIME NT STATION ■... * :-; ** ■ WILLIAM. E. MARTIN VICTOR V. RENDIG ARTHUR D> HAia LESTER J. BERRY, BUIKTIN 81S V FERTILIZATION OF FORAGE CROPS . . . on irrigated pastures in California is influenced by the state's varied climatic conditions and soil types. Nitrogen, phospho- rus, and sulfur are the principal nutrients involved. Over the past 10 years, numerous field tests with fertilizers have been conducted on cattle ranches throughout California. Results of the tests have been released in the various areas either as progress reports or as county publications. This bulletin brings together and summarizes the more im- portant findings for the three major forage areas: northeastern California; the coastal and north central valleys; and the San Joaquin Valley. Submitted for publication June 4, 1964. THE AUTHORS: William E. Martin is Agriculturist, Agricultural Extension, Davis. Victor V. Rendig is Professor of Soils and Plant Nutrition and Soil Chemist in the Experiment Station, Davis. Arthur D. Haig was formerly Assistant Agriculturist, Agricultural Extension, Davis. Lester J. Berry is Agriculturist, Agricultural Extension, Davis. JULY, 1965 FERTILIZATION of IRRIGATED PASTURE and FORAGE CROPS in California William E. Martin • Victor V. Rendig • Arthur D. Haig • Lester J. Berry Irrigated pasture and forage crops for hay or grazing are grown under a wide variety of climatic conditions in Califor- nia. Whether the crops are harvested by machine, for hay, or by grazing animals, depends upon the rancher's forage needs. In northeastern California, forage crops are commonly grown in high valleys, re- ferred to as mountain meadows. These meadows are usually at elevations of 3,000 to 4,000 feet, and are irrigated by spring and winter runoff from melting snows. A hay crop is commonly harvested in late spring or early summer, and the regrowth grazed throughout the summer and fall. The forage may be either from unim- proved meadows composed of native species of grass, sedges, and clovers, or from improved meadows seeded with tre- foil, alfalfa, or clover, and grasses such as tall fescue, orchardgrass, and others. Ce- real rye or oats are occasionally seeded into a legume stand to provide extra for- age for hay or grazing. The irrigated pastures in the central valley and the coastal areas are usually made up of a mixed community of plants, including legumes such as Ladino clover, trefoil, or alfalfa, and grasses such as rye- grass, orchardgrass, or tall fescue. Al- though pastures in these areas are grown primarily for grazing, hay crops are some- times taken at the time of the spring flush of growth when a surplus of forage may occur. Ladino clover stands are often grazed before a seed crop is taken. In the southern San Joaquin Valley, irri- gated pastures are dominated by warm- season species such as dallisgrass or the bermudagrasses. In these areas irrigated pastures are usually grown on the poorly THE PROBLEM drained soils in the trough of the valley, which are commonly saline or alkaline or both. Narrowleaf trefoil is often planted with the grasses, but makes little forage under saline or alkaline conditions. Salina strawberry clover is now being tested for use under such conditions. Fertilization problems of irrigated for- age crops usually involve nitrogen, phos- phorus, and sulfur. Many of the soils on which irrigated pastures are grown are old red terrace soils deficient in phos- phorus. In the northern areas of the state, deficiencies of both phosphorus and sulfur are common. Ideally, an irrigated pasture that is a mixture of grasses and legumes will need relatively little nitrogen since the legume component, if vigorous and healthy, fixes nitrogen from the air through the action of the symbiotic bacteria in nodules on the roots. Subse- quently, the roots slough off and de- compose, releasing nitrogen to the grass portion of the pasture association. Leg- umes such as Ladino clover, trefoil, or alfalfa are used both to provide a high protein component in the forage and to supply nitrogen to the grasses. In areas where legumes grow poorly or where few are present, nitrogen fertilizers may be used profitably to keep the grass species productive. One of the recurrent problems in the central valley has been a reduction in growth of clover pastures during the hot summer months, particularly on the phosphorus-deficient hardpan soils. In some areas, pastures on thin soils must be irrigated at almost weekly intervals. This creates problems in maintaining fertility, particularly where nitrogen applications have been made. [3 NORTHEASTERN CALIFORNIA- NATIVE AND IMPROVED FORAGE CROPS In Modoc, Lassen, Siskiyou, and Plumas counties, and in parts of Shasta County, both native meadow forage and improved pasture species are used for hay and graz- ing. Much of this area of mountain val- leys at 3,000 to 4,000 feet is acutely defi- cient in sulfur (Martin, 1958).1 Parts are also deficient in phosphorus and boron. Native and planted grasses have re- sponded spectacularly to added commer- cial nitrogenous fertilizers both where legumes are sparse and where more pro- ductivity is desired than the grass-legume mixture provides. Fertilization of Native Mountain Meadow Forage for Hay or Grazing Fertilizer tests and demonstrations were carried out in the area to determine what forms of nitrogen are most effective on 1 See "Literature Cited" for citations referred to in the text by author and date. native grass-sedge meadows and how much nitrogen can be most economically used (Bedell, 1962). Does the area need nitrogen and sulfur? The first group of tests, from Modoc and Lassen counties, shows the import- ance of using a sulfur-containing, nitroge- nous fertilizer. In these demonstrations straight nitro- gen carriers such as urea or ammonium nitrate were compared with nearly equal nitrogen from ammonium sulfate (table 1). The nitrogen and sulfur treatment gave higher yields than the nitrogen in six of the seven paired comparisons. It is be- lieved that nitrogen was the first factor limiting growth, and that additions of sulfate were required for greater growth. Since ammonium sulfate usually costs no more per pound than other forms of nitro- gen, it is recommended for this area in- stead of straight nitrogen materials. Table 1 . Effects of Nitrogen and of Nitrogen plus Sulfur on Yield of Mountain Meadow Forage (Modoc and Lassen Counties) County and farm Year Average yield of forage from: No fertilization 65 lb. N/acre 69 lb. N/acre 103 lb. S acre Modoc County: Cockrell Grove Bishop Caldwell "J&D" Lassen County : Nash Albaugh Average . . . 1953 1953 1953 1953 1954 1953 1962 tons /acre 1.51 2.78 2.26 1.70 0.90 1.53 2.06 1.82 tons /acre 2.14 4.55 5.52 4.10 1.91 3.19 3.26 3.52 tons /acre 2.85 5.30 5.05 4.25 2.30 3.64 3.49 3.84 [4] Does it pay to add phosphorus? Further comparisons were made to de- termine whether the addition of phos- phorus in ammonium phosphate sulfate (16-20) gave better yields than did am- monium sulfate. In these tests, 12 of the 16 comparisons gave numerically higher yields from such addition of phosphorus (table 2). The economic effectiveness of phos- phorus additions was evaluated by com- paring profits from use of ammonium sulfate with those from (16-20), assuming a hay value for the increased hay at $15 per ton. Only five of the tests gave enough extra hay to show appreciable profit from use of phosphorus. Had a value of $10 per ton of hay been used, only two of the 16 phosphorus treatments would have paid the cost of adding phosphorus. The inclusion of phosphorus in com- mercial fertilizers supplying nitrogen and sulfur is recommended only for locations where its need has been established by field test or by soil analysis. Added phos- phorus will no doubt be required after meadows have been cropped longer and more intensively. Trials in the Sierra and Indian valleys of Plumas County have shown more fre- quent benefit from additions of phos- phorus to nitrogen-bearing fertilizers. How much are yields raised by higher nitrogen rates? Sixteen tests to determine the most economical nitrogen rate were carried out, with at least one test in each major area where native mountain meadows are fer- tilized. The results are shown in figure 1. Results from seven tests with ammonium sulfate in Modoc County, 1953, indicated somewhat higher efficiency than has been obtained in subsequent years. Data from later groups of well-replicated rate tests indicate that we might expect approxi- mately one-half ton of dry material from 20 pounds of nitrogen, three-quarters ton from 40 pounds of nitrogen, and about 1.5 tons where 80 pounds were used. Two nitrogen rate tests to determine practical upper limits of fertilization were carried out in 1961 in Modoc County. Nitrogen rates were increased stepwise from 21 to 336 pounds of nitrogen per acre (as 100 to 1,600 pounds of ammo- nium sulfate). Average yields from the two plots form a smooth curve that levels off at the higher nitrogen rates. Results from other county tests were generally similar at the lower rates of nitrogen. Where phosphorus is needed, how much should be used? Data obtained in 1961-1962 from three tests with ammonium phosphate sulfate, in Plumas County, indicate that the nitro- gen responses with this carrier are about the same as those obtained with ammo- nium sulfate on soils with adequate phos- phorus. Few data are available on the amounts of phosphorus that should be added to nitrogen and sulfur when phosphorus is needed. Seventeen pounds of phosphorus (40 P205) per acre, in two comparisons in 1962 and 1963, respectively, did as well as 44 pounds (100 P2Os). How do fertilization and time of cutting affect protein content of the hay? Both fertilization and time of cutting may affect crude protein content of meadow hay. On three ranches in Modoc County, hay was cut three to four weeks earlier than usual in experimental plots, and samples were analyzed for crude pro- tein (N x 6.25). These values were com- pared with hay samples taken from plots cut at the usual July harvest date. Results of this study, given in table 3, show that time of cutting was of far more impor- tance than fertilization in changing the protein content. Hay cut in June at a relatively immature stage gave average values of about 12 per cent crude protein, while late-cut samples showed values of only 8.5 to 9 per cent, or two- thirds as much protein. At each date, high nitro- gen treatments tended to increase protein slightly. These results are similar to re- sults reported in mountain meadow ferti- lization studies carried out in Colorado (Willhite, Rouse, and Miller, 1955). [5] o O o Cflp4 ■sa 3 O ^ W- o -o 0) >- c o (/> 3 ,. — ., v. «« O 0) -C +- Q. c J O o a. u i O 3 to M- D ") J= (/> to r -o 0) c O) O o s u. C .■♦; 0) Z o o -J "73 O C O Si o w JC Q. to O ^ H t- O cq th ** © co s s s s C-" i-l CD O W tf3 »» t- H t- ^ lO (N ic m Q jn o tH OO ift t- 00 tH O I - o o r- cn ^ tH CD CO CO CO Tj« CD T}< 05 cp OJ ^ tH tH © (N CO CO CO CO CD CN i CO t- 00 CO CO CO C7> 00 CN C- «*< 2 o co CO tH CO CN (N CO O tN O CO O t- CN lO CN lO CO lO ^ 00 CO CO t- o CN CO CN CO 00 CN "tf CN «tf CO CO H 00 t» CO O lO t- t- CN t- O tH OS t- T}i tH tH CN tf M W lO co o> o o o o w o S o O ! O X> © o £ W £h t3 ••-< P » < S M w II II SI a gSS. - .^mc^m h fe © » i •►•Sap. «S-gS888 sflJJi H « © 45 » « 2.5 — / ^961 2 NS plots / £ ' f ' */ 2 - V / s / / Jf / / ^ / / 1961,1962,1963 / j j Shasta and Lassen J? / ' / 4 NS plots / ''/ / \ >' f ^ 1 / ///^ 0 by r f 1 1 1 L_ 1 1 _ _L 150 200 Nitrogen applied (lb. per acre) Fig. 1 Graph shows how much yields are raised by higher nitrogen rates. How efficiently does meadow forage use fertilizer nitrogen? Tests in both Lassen and Modoc coun- ties show that successively higher yields with increasing nitrogen up to 168 pounds per acre were obtained with no significant effect on protein values. Cal- culation of nitrogen recovered in forage shows that at low rates the extra nitrogen harvested in the hay amounted to 60 to 80 per cent of the amount added in the fertilizer (tables 4 and 5). As the rates of nitrogen were increased, the apparent re- covery decreased to only 26 to 28 per cent at very high nitrogen rates (table 5). Table 3. Effect of Time of Cutting and Applied Nitrogen* on Crude Protein in Forage (Modoc County, 1962) Amount of crude protein from: Ranch Early cutting (June) Late cutting (July) HighN (160 lb.) LowN (0-80 lb.) HighN (160 lb.) LowN (0-80 lb.) Weber per cent 14.7 11.9 11.6 per cent 12.7 11.1 11.1 per cent 9.8 7.4 9.7 per cent 8.9 Fee 8.0 Fluornoy 8.7 Average 12.7 11.6 9.0 8.5 * As ammonium sulfate. [7] 50 100 150 200 Nitrogen applied (lb. per acre) 250 300 Fig. 2. How to measure maximum profit from fertilization of mountain meadow. Hay at both locations was cut in late July, and crude protein was increased sig- nificantly only with the very highest nitro- gen treatment. Fertilization with nitrogen may reduce clovers In the Modoc test, clovers and grasses were separated. The percentage of clovers in the hay decreased with increasing nitro- gen treatments. This decrease was not offset by the addition of phosphorus at the 80-pound nitrogen rate. How to determine the most profitable rate of nitrogen In the most profitable fertilizer pro- gram, a maximum profit over cost of fer- tilizer is achieved. To make such an evaluation, a value must be placed upon the extra forage resulting from fertiliza- tion, and the cost of the fertilizer required to bring about the observed result sub- tracted from that value. Such a calcula- tion is shown in figure 2, with actual data from two Modoc County tests where rates of nitrogen were increased up to 360 pounds per acre. In this chart the value of the increased hay resulting from fertiliza- tion is plotted as dollars of value at a price of $15 a ton. A maximum of nearly $40 increased value was achieved. A second line indicates the costs of the nitrogen used. The calculated cost is charged at 15 cents per pound of nitrogen applied. The cost of the nitrogen applied continues Table 4. Amount of Crude Protein and Apparent Nitrogen Recovery in Forage (Lassen County, 1962, Swickert Ranch) Fertilizer applications (lb. per acre) N applied Hay yield Crude protein* N harvested in hay Extra N due to treatment Apparent N recovery None lb. /acre 42 84 126 80 lb. /acre 2,695 4,475 6,033 6,958 6,377 per cent 7.7 8.1 8.3 7.5 7.9 lb. /acre 33.3 62.1 80.3 83.5 80.9 lb. /acre 28.8 47.0 50.2 47.6 per cent Ammonium sulfate : 200 69 56 40 59 400 600 16-20: 500 * Changes not significant at 5 per cent level. [8] to increase in a straight line while the value of the increased hay levels off. At 260 pounds of nitrogen per acre the cost of the nitrogen exactly equaled the value of the increased hay. At the lower rates of nitrogen, the value of the in- creased hay was increasing faster than was cost of materials. At the higher rates, the cost of the nitrogen was increasing faster than the value of the hay. The maximum profit, represented by the dif- ference between the two lines, was great- est at about 110 pounds of nitrogen per acre, but did not change rapidly because the value line was almost parallel with the cost line between 90 and 120 pounds of nitrogen per acre. Price of fertilizer nitrogen and value of forage must both be considered in deciding how much nitrogen should be used. Data for the Modoc County high nitrogen-rate tests show striking differ- ences in "fertilizer profits" after increase in forage is evaluated and cost of nitro- gen deducted. The curve in figure 2 shows a single price-value relationship. The curves in figure 3 illustrate how the "most profitable rate" and "profit over cost" change with different nitrogen prices and changing values for forage. It will be noted that the "profit per acre" curves have broad peaks, and that for any value of forage, profit varies but little over a fairly wide range in rate of application. Several rates of nitrogen, dif- fering by 10 to 20 pounds per acre and $1.50 to $3 in cost, may give profit values of within 10 to 15 cents of each other. In other words, the point of maximum profit should more properly be referred to as "zone of maximum profit" in which value of extra yield is about equal to cost of fertilizer required to produce each added increment. In this zone we are essentially trading dollars. It is clear, however, that as forage in- creases in value and nitrogen decreases in price, much greater profits from ferti- lization are possible and high rates of nitrogen application are feasible. At lower forage values and higher priced nitrogen, the reverse is true. Fertilization of Improved Grass-Legume Mixtures Pasture species such as clover, trefoil, and alfalfa have frequently been planted with grass for either hay or grazing in many areas of northeastern California. Deficiencies of phosphorus, sulfur, and boron have been common, particularly on the alfalfa component of the forage mix- ture. Application of these nutrients alone or in combination has often stimulated the legumes sufficiently to keep the grass reasonably well supplied with nitrogen. Table 5. Amount of Crude Protein and Apparent Nitrogen Recovery in Forage (Modoc County, 1961, Fee Ranch) Fertilizer applications (lb. per acre) N applied Hay yield Legume in hay Crude protein N harvested in hay Extra N due to treatment Apparent N recovery None Ammonium sulfate : 100 200 400 800 1,600 16-20: 500 lb. /acre 21 42 84 168 336 80 lb. /acre 4,540 6,080 6,980 7,700 9,220 9,080 7,280 per cent 21.6 17.5 5.7 7.4 3.5 not deter- mined 6.3 per cent 8.4 8.1 7.8 8.4 7.4 10.2 7.4 lb. /acre 61.3 79.0 87.3 104.0 108.0 148.0 85.9 lb. /acre 17.7 26.0 42.7 46.7 86.7 24.6 per cent 84 62 51 28 26 31 [9] Maximum profit 50 00 150 Nitrogen applied (lb. per acre) 200 250 Fig. 3. Effect of forage value, nitrogen rate, and price on profit from meadow fertilization. Responses to sulfur sulfur are the most common. The yield are often spectacular figures in table 6 show the response ob- Sulfur is usually the first deficiency to tained from applications of gypsum to be encountered, and responses of the leg- irrigated alfalfa, grass, and clover-grass ume, in a grass-legume mixture, to added mixtures in Lake, Modoc, and Shasta Table 6. Effect of Sulfur on Yield of Improved Legume-Grass Irrigated Pasture Mixtures County, year, and crop Fertilizer Yield (dry wt) Gain from sulfur Cost of sulfur Cost per ton of extra forage Lake, 1955: Orchardgrass, trefoil, » and alfalfa v None 500 lb. gypsum (90 lb. S/acre) lb. /acre 1,634 5,939 lb. /acre 4,305 $5.00 $2.33 Shasta, 1961: Orchardgrass, \ ryegrass, alfalfa, and trefoil \ None 200 lb. gypsum (36 lb. S/acre) 1,790 4,100 2,310 2.00 1.73 Modoc, 1956: Alfalfa, cereal rye, \ oats and v None 400 lb. gypsum (72 lb. S/acre) 3,312 4,511 1,199 4.00 6.60 [10] Table 7. Effect of Boron and Phosphorus on Yield of Irrigated Alfalfa-Grass Forage (Siskiyou County, 1958) Fertilizer Dry material (first cutting) applications (lb. per acre) Alfalfa Grass Total None lb. /acre 1,413 2,336 2,268 3,308 lb. /acre 1,090 1,110 971 897 lb. /acre 2,503 600 single superphosphate 3,446 100 borax 3,239 600 single superphosphate plus 100 borax 4,205 counties. Note that the additional forage was produced at a fertilizer cost of $2 to $6 per extra ton of hay. Similar results have been observed in many areas on non- irrigated, legume-grass forage plantings. Boron and phosphorus deficiencies are important in some areas Boron deficiency occurs at a number of locations in Shasta and Scott valleys in Siskiyou County, often along with a de- ficiency of phosphorus or sulfur or both. Boron-deficient alfalfa, either alone or with grass and pasture mixes, shows char- acteristic bright yellow terminal leaves, fails to set seed, and shows die-back of terminal growing points in severe cases. Results of boron and superphosphate ap- plications to alfalfa grass mixtures used for hay and grazing are shown in table 7. Both single superphosphate (to supply phosphorus and sulfur) and boron were required to correct the three nutrient de- ficiencies at this location. Applied phos- phorus and boron tend to remain effective for several years, whereas gypsum or other sources of sulfur must be applied annually or at least every two years. COASTAL AND NORTH CENTRAL VALLEYS— LEGUME-DOMINANT PASTURES Legume-dominant pastures are common throughout the Sacramento Valley, the northern San Joaquin Valley, and in the cooler valleys adjacent to the Pacific coast. Here Ladino clover and trefoil are the principal legumes, with ryegrass, orchardgrass or tall fescue the most com- mon grass species. Many of the locations devoted to irrigated pasture in the north- ern part of the central valley are on reddish, hardpan soils or old claypan soils commonly deficient in available phos- phorus and sulfur. It has been an accepted practice in many of these areas to fertilize the pastures with single superphosphate (which contains both phosphorus and sul- fur) in an effort to stimulate the clovers. If the clover responds vigorously, it may be expected to provide additional nitro- gen for the grass component of the pas- ture association. Considerable grass should be present to reduce the bloat hazard associated with a high percentage of clover in the forage. A series of fertilizer tests were set up on irrigated pastures to find out: (1) what responses to fertilizers could be antici- pated; (2) how much phosphorus could most profitably be used; and (3) whether additional nitrogen could be economically used to increase growth. This study sought reliable information about the effect of fertilizers on produc- tion of seasonal forage and on the shifts in individual plant species present. The test areas were harvested at intervals through- [ii] Table 8. Yield of Forage with Various (Shasta County, 1950) Fresh weight of forage with: Ranch and soil type No fertilizer (control) N S Nand S P and S i Carpenter; Red Bluff loam Hopson; Columbia loam lb. /acre 3,585 6,410 lb. /acre 5,080 8,830 lb. /acre 13,960 11,840 lb. /acre 16,865 10,360 lb. /acre « 7,760 < 9,530 * N = 50 N per acre from 150 lb. ammonium nitrate. S = 76 S per acre from 400 lb. gypsum. P = 73 P (168 P2O5) from 400 lb. treble superphosphate. K = 100 K (120 K2O) from 200 lb. muriate of potash. out the growing season by mowing strips through each treated plot with a mobile forage harvester or power mower. Repli- cated randomized block experiments were used. The experimental areas were fenced and protected from grazing. In later tests the entire area was grazed by cattle as soon as the test samples had been re- moved. In this way plots were harvested at the normal intervals throughout the grazing season and were also subjected to the impact of rotation grazing. Yields of the experimental forage plots were measured by weighing the fresh material clipped from a measured strip cut across each treated area. After the fresh material was weighed, samples were taken and placed in plastic bags for hand separation into component plant species. In this way it was possible to measure how fertilizers affected individual yields of the legume and grass species in the mixture. Chemical analyses of forage samples were made to measure the recovery of added fertilizer by pasture plants and to determine the influence of fertilization upon plant composition and forage qual- ity. Soil samples were taken to establish phosphorus status prior to fertilization (Ohenetal, 1954). Table 9. Effect of Nitrogen and Phosphorus on Forage Yields County, soil series, and year Bicarbonate- soluble soil P (HCOa-P) Nutrients applied Total annual yield, dry wt. (untreated) N (P2O5) P Napa, Coombs, 1954 p.p.m. 4.0 30.5 8.1 4.4 2.2 4.9 11.7 lb. /acre 100 52 150 150 200 180 100 210 80 lb. /acre (60) 26 (66) 29 (100) 44 (80) 35 (80) 35 (160) 70 (320) 140 (80) 35 (80) 35 lb. /acre 3,538 9,471 Yolo, Capay, 1956 Solano, Solano, 1956 3,563 Placer, Rocklin, 1956 3,155 Sacramento, San Joaquin: 1956 5,804 J 5,903 6,345 8,074 i 3,126 1957 1958 Glenn, Tehama, 1957 Napa, Dublin, 1961 * Significant benefit from nitrogen at 5 per cent. t Addition of phosphorus gave significant increase in yield over untreated or nitrogen only. [12] •Nutrient Combinations" • N, P, and S P, K, and S N, P, K, and S lb. /acre * 9,665 11,250 lb. /acre 16,840 12,480 lb. /acre 16,455 15,260 What Fertilizer Nutrients are Needed? Tests have indicated that nitrogen, phos- phorus, sulfur, and potassium are the fer- tilizer nutrients most likely to improve growth of pasture forage. Results from replicated exploratory tests in the Ander- son-Cottonwood area of Shasta County are shown in table 8. In both tests nitro- gen alone increased yield, but nitrogen plus sulfur gave higher yields. The addi- tion of phosphorus greatly improved yield in the Carpenter test but only slightly in the Hopson test. Application of in Legume-dominant Irrigated Pastures " Yield increase from: w P only N +P N only lb. /acre lb. /acre lb. /acre 2,530f 4,736* 1,570* ► 261 1,746* 286 1,627* 1,563* l,154f 2,537*f ► 2,008f 3,804*f 1,965* 2,775f 4,424*f 1,180* 3,035f 3,648*f 1,105* t 871 2,246*f 1,284* ► 47 636 *f 465* potassium did not result in any consistent benefit. Potassium responses have only rarely been observed in the major irri- gated pasture regions although local areas in Siskiyou, Butte, and Stanislaus coun- ties are known to benefit from this nu- trient (McCollam, 1948; Ulrich, 1940). Tests with nitrogen and phosphorus Nine tests were carried out on legume- dominated pastures, with five to seven cuttings, over entire seasons. Nitrogen (ammonium sulfate), phosphorus (single superphosphate), and a combination of both were used. Results are shown in table 9. Total seasonal yields without treatment varied from about 3,500 pounds dry matter to somewhat over 9,000 pounds. Every test showed significant in- creases in yields as a result of fertilization. Three of the tests, in Yolo, Napa, and Solano counties, were on soils sufficiently supplied with phosphorus, so that no sig- nificant increases in yield resulted from added phosphorus. In the remaining six tests, soils were deficient in phosphorus, and yields were increased by fertilization with that nutrient. Nitrogen plus phos- phorus increased yields on the phos- phorus-deficient soils more than did nitrogen alone. Similarly, yields were greater with nitrogen plus phosphorus than with phosphorus only. Analysis of soil samples from the tests in this study indicates need of phosphorus fertilization only on soils with less than 4.9 ppm of phosphorus (using the Olsen bicarbonate extractant). Recent sampling of the pas- ture plots in the north coast and mountain areas suggests that in those regions a con- siderably higher threshold value will have to be used. Irrigated pastures throughout much of northern and central California are grown on relatively shallow, red hardpan soils or on soils with a claypan layer. These soils are commonly phosphorus-deficient. At any location, the magnitude of the re- sponse to phosphorus will depend on the phosphorus level in the soil. This in turn will be affected by duration of cropping, previous fertilizer history, and phosphorus fixation characteristics of the soil. [13] Table 10. Effect of Superphosphate on Yield of Legume-dominant Irrigated Pasture Mixture on Phosphorus-deficient Soils County, soil series, and year Soil phosphorus (HCOr-P) Total annual yield, dry weight (untreated) Increase in dry weight of mixed forage from: 35 P (80 P206) 70 P (160 P206) Placer, Rocklin, 1956 p.p.m. 4.4 2.2 4.9 3.0 3.2 lb. /acre 3,155 5,804 8,074 5,475 9,009 lb. /acre 1,154 2,008 871 509 1,742 lb. /acre 1,235 Sacramento, San Joaquin, 1956. . . Glenn, Tehama, 1957 2,858 1,232 Solano : Capay, 1956 694 Tiindsey, 1958 2,523 Average 6,303 1,257 1,708 Such variation in response was shown in tests conducted in the Sacramento Val- ley (table 10). In these tests, 400 pounds of single superphosphate (35 P) applied in early spring gave increases in yield of from 500 to about 2,000 pounds for the entire season. Doubling the phosphorus further increased the yield by only about 50 per cent. The data show the magnitude and range of response to be expected on phosphorus-deficient soils provided a re- sponsive legume is present, capable of making improved growth under the pre- vailing climatic and soil conditions. EFFECT OF FERTILIZERS ON GRASSES AND LEGUMES Inorganic ammoniacal or nitrate nitrogen fertilizers, alone or with phosphorus where needed, nearly always cause an in- crease in growth of the grass in mixed legume-grass stands. Normally, grass in a pasture association is provided with nitrogen by the decomposition of soil organic matter and of legume roots and nodules. The amount of nitrogen so pro- vided, however, is rarely as much as the grass could use. Consequently, grass growth often increases with nitrogen ap- plication. Nitrogen rarely stimulates legumes directly, and single applications seldom have any permanent effect upon the stand of legumes in a pasture mixture. How long do effects of nitrogen last? Single applications of commercial in- organic nitrogen usually remain effective only a few weeks, or until the forage stimulated by that nitrogen is removed. Tests with nitrogen at various rates up to 100 pounds per acre show little, if any, response after the first cutting or grazing. This is illustrated by the 1956 yield curves from Sacramento County (fig. 4) which show the increases in grass yields due to nitrogen either alone or with phosphorus. Ammonium nitrogen fertilizers applied in March were effective at the time of the first cutting in April. By the time of the next cutting, in May, yields had been re- duced to the level of the untreated plots. The same material applied after the second cutting increased yields for only about a month. In 1957, more frequent, smaller applications of ammonium sulfate gave more regular response. Results similar to those for 1957 in figure 4 were obtained from spring appli- cations of nitrogen in tests in Yolo and Solano counties. These findings indicate [14] Season totals (lb. /A) Increase 1,856 2,646 Control Season totals (lb. /A) D 50 1957 o CO Z Check 3,444 Increase 1 N210 6,030 2,586 -a 40 o CO I N210, P70 7,761 4,317 a> Q. o 7 CO : z i o CO Z 1 a. 20 / * X >Ny^ \l 1 -a 10 1 /J r, 'w ^U- CD < 7T. N only >- 0 1 ^ C r\ntrri\ M arc h Ap ril May June July Aug. Sept. Oct. m ^ V-Uim ui Fig. 4. Increase in yield of grass as result of applied nitrogen. Test conducted on Lewis ranch, Sacramento County, shows how long a nitrogen application lasts. that a single application of nitrogen, even as much as 100 pounds per acre, will last only about a month in a pasture that is being grazed and watered regularly. Nitrogen often crowds out clover Continuing nitrogen application may have an important effect on the relative growth of grasses and legumes. In an ex- periment at Davis in 1957, various rates of ammonium sulfate were applied to a [ newly established, mixed pasture of Ladino clover and orchardgrass (Peterson and Bendixen, 1961). Results of the first season's test showed a definite increase in total yield of forage in response to nitrogen (table 11). The ni- trogen treatments were continued for a second year with no increase in total yield. Orchardgrass had replaced the Ladino clover in areas where continuing applica- tions of nitrogen had been made during the summer months. In unfertilized sec- 15] Table 11. Yield of Ladino-Grass Forage as Influenced by Nitrogen Applied on a Soil with Adequate Phosphorus Yield of forage Nitrogen application (lb. per acre) First season total* Second season Grass Ladino Total 0 tons /acre 2.84 3.70 3.94 4.79 tons /acre 1.57 2.09 2.58 2.49 tons /acre 2.11 1.52 1.27 1.06 tons /acre 3.68 80 3.61 120 3.85 160 3.55 * No species separation made during first season. tions, yields of the grass-legume mixture were slightly under 4 tons per acre, and the clover percentage remained high throughout the entire season (fig. 5). Ni- trogen definitely increased growth of grass, but the increase was almost exactly offset by a reduction in the growth of clover, and the total yield was no greater than that of the check (table 11). This test on a productive, high-phos- phorus soil shows that nitrogen-stimu- lated grass can crowd out clover. Nitro- gen influences the balance of grasses and legumes because low nitrogen limits grass but not clover, while at high nitrogen levels grass competes with clover for water, space, and light and remains domi- nant so long as the high nitrogen supply is maintained. Phosphorus benefits both grasses and legumes On soils that are moderately deficient in phosphorus, applications of this nu- trient usually stimulate the legumes pres- ent, while applications of nitrogen gen- erally improve the growth of grass. A treatment with both nitrogen and phosphorus usually gives a better yield of grass than does nitrogen alone. When separate tests were made on grasses and legumes with nitrogen and phosphorus (table 12), applications of phosphorus to phosphorus-deficient soils in three coun- ties increased the growth of clover in every instance. Applications of nitrogen did not benefit the clover, but did in- crease the growth of grass. Yields of grass from nitrogen plus phosphorus were greater than from nitrogen alone. Even with phosphorus alone, some slight in- crease in grass growth occurs (probably because clovers are stimulated and, dur- ing the summer, make available to the grasses some of the nitrogen fixed through extra root growth and nodule activity). Trefoil is often the dominant legume on phosphorus-deficient soils. If Ladino clover is present, it is usually a minor constituent. Applications of phosphorus to some soils often cause the Ladino to "get going" and crowd out the trefoil. If no Ladino is present, phosphorus appli- cations can and do greatly stimulate tre- foil growth. Frequent watering also favors Ladino clover, while longer intervals be- tween irrigations give trefoil an ad- vantage. Effects of continuing nitrogen and phosphorus treatments where phosphorus is needed When phosphorus is deficient, both nitrogen and phosphorus fertilizers may affect the botanical composition of the pasture mixture. The Sacramento County test was car- ried out for three successive years to find out whether maintaining a very high phosphorus level in the presence of nitrogen would reduce the crowding of legumes by nitrogen-fertilized grasses. Each season six or seven cuttings were made, and plant separations were made [16] £ 0) o C o Q. 3 s_ d -C Q. «/> O c D C a> o> o o a) UJ v.. o (D J) -Q D ++ ++ ++ © 00 00 ^ 00 IO Oi CN IS O O) t* CN 00 © 3 o o CO CO t> O © *H O IO e* oocgn iH O CO 00 00 CD c- H £ CO CO 00 IO CO Tt« IO w t- © t» ++ ++ ++ ++ ++ CO 00 N H H o o o H CO t- t« co oo i* t> CO o CO CD 00 tO t> co o e3 ed oo ^ io © O -^ rH N H 00 O 5 1 £ y-t ON IO tJ* CN o en ■* o «s e3 CO CD CO O e3_ "S ►^ £ iH CO CM i-i 2 (fl is "3 0 § a © iH CO CO E*» CN O "tf oo *© eS rtO t N M H £ iH iH iH tH ++ -M- ++ ++ 2 © » © co TJ iH CD ,2 © | IO © 1 a o „ C3* S p 4 '8 .2 o CO "o § £ Ml .p S3 d iQ g s o CO O O o O eef o a> 1 i 1 ii 3 fc Ah OQ for each cutting to find out how each kind of plant had been affected by fertiliza- tion. Results from the second year of treatment (1957 season) are shown in figure 6. Yields were calculated as pounds per acre per day, to show changes during the season and help visualize the results in terms of animal use. A cow or steer needs 20 to 25 pounds of dry matter each day. On this basis, the untreated pasture (fig. 6) would carry only about an animal per acre, with a surplus of feed in May and June. The heavily phosphated pasture would have carried nearly two animals per acre for most of the season. Figure 6 also shows that nitrogen treatments alone caused a big increase in grass growth, especially in May, that con- tinued for most of the summer. Ladino clover and trefoil were greatly reduced by straight nitrogen treatments. Phosphorus treatments seem to have increased grass growth somewhat in the spring, but nearly doubled Ladino clover production. When both nitrogen and phosphorus were used, grasses really took over. Ladino was better than in the control plot, but much less than where straight phosphorus treatment had been made. Trefoil was almost completely eliminated. Over a three-year period (fig. 7), nitro- gen, even with adequate phosphorus, caused a decrease in the proportion of legumes in the mixture. Furthermore, while nitrogen alone may favor grass, ni- trogen plus phosphorus apparently makes grass grow even better. Increasing amounts of phosphorus were applied to find out whether a high level of phos- In this publication, the nutrients ni- trogen, phosphorus, and potassium are expressed as actual amounts of the ele- ment applied. Since phosphorus and potassium have usually been expressed as P2Os (phosphorus pentoxide) and K20 (potassium oxide), respectively, the alternative values are also given. The conversion scale at the right should prove helpful in determining actual amounts of the element from the amount of fertilizer applied. FERTILIZER CONVERSION SCALES Element to Oxide (Pounds or Per Cent) PHOSPHORUS P [18] PHOSPHORUS PENTOXIDE P,05 POTASSIUM K POTASSIUM OXIDE M -ir-100 40— E 35- -90 80 30- _E-60 25- = 20 15-: 10— r 5- =-70 -=r50 -40 r-30 --20 .-10 O-E-0 t-100 80-: lE-90 70- =r-80 60- 50 --70 P-60 40 -: 30- = 20-: 10-: ZE-50 1-40 -E-30 -20 --10 April 22 May 21 June 17 July 16 Aug. 13 Yield (lb. per acre per day) Sept. 1 1 Oct. 11 Fig. 5. Second-year effect of nitrogen on percentage of grass in Ladino-orchardgrass pastures at Davis. Arrows indicate time at which 40 pounds of nitrogen increments were added. Grass, 3,444 CHECK Ladino, 1,891 5,963 Trefoil, 628 Ib./A P70 Grass, 4,560 Ladino, 3,777 8,738 Trefoil, 401 Ib./A March I April May |june I July I Aug. I Sept.] Oct. I March j April] May] June] July I Aug. | Sept.] Oct N180 Grass, 6,030 Ladino, 924 7,143 Trefoil, 189 Ib./A N180 P70 Grass, 7,761 Ladino, 2,400 10,387 Trefoil, 226 lb. A Fig. 6. Effect of nitrogen and phosphorus on yield of separate pasture species. [19] phorus would prevent crowding out of legumes by nitrogen-fertilized grasses. Even at 140 pounds of phosphorus (320 P2Os), legume yields continued to de- crease. In 1958, yields from the high- phosphorus treatment were about the same as those from nitrogen and phos- phorus in combination. Where both nitro- gen and phosphorus were applied, the proportion of legumes in the mixture was much less, and nitrogen-fixing capacity was reduced correspondingly. Tons/A NITROGEN AND PHOSPHORUS SHIFT Yields of Legumes and Grass 1956 1957 1958 Crude Protein of Whole Forage 1958 Check ^ 4- 3- 2- ! kST r e F 0 1 L 31 kv^v^vvvvw . AGRASSX LADINO 17.5% Protein 15.7% Protein 5- n§ 4- NP 3 - im -?- ^ n 2- 18.8% Protein 1 - LIAVW.W^W.^1.* «™ 4- lit Hi 3- lllll -» ?- 19.9% Protein 1 - ^^^^^ N at 200 lb/A Pat 35 Nat 180 lb/A Pat 70 Nat 100 lb/A Pat 140 Fig. 7. Influence of continuing nitrogen and phosphorus treatments on yields of grass and legume and on crude protein content of whole forage. [20] EFFECT OF FERTILIZATION ON PROTEIN AND PHOSPHORUS CONTENT OF FORAGE The protein content of legumes such as trefoil and Ladino clover is much higher than that of grasses. Factors that cause an increase in the amount of clover in forage tend to increase the protein content of the entire pasture mixture. Earlier studies (Rendig, Martin, and Smith, 1950) of pasture fertilization in the Anderson-Cottonwood district of Shasta County showed that phosphorus fertilization increases total growth, alters relative amounts of grass and legumes present, and materially changes the chem- ical composition of the forage. The crude protein of whole forage was increased from 16.3 to 19.3 per cent by phosphate application, principally because of a larger proportion of high-protein Ladino in the mixture. However, there was also a slight increase in protein content of the grass. The phosphorus content of both Ladino and grass was increased by fer- tilization, with the grass showing some- what higher phosphorus values than the legumes. In the Sacramento County test, yields were materially changed by fertilization with either nitrogen or phosphorus (fig. 7). The phosphorus fertilization increased the amount of high-protein clover in the mix- ture, thus increasing somewhat the crude protein content of the whole forage. Ni- trogen alone increased the protein con- tent of the grass very slightly, but tended to decrease the proportion of high-protein clover in the mixture. As a result, the pro- tein content of the entire pasture mixture was reduced by nitrogen. The effects of continuing nitrogen and phosphorus treatments on the composi- tion of forage and yield of individual species (Napa County) are shown in table 13. First- and second-year responses were compared. Both seasons' data show that the protein content of whole forage was increased by use of phosphorus because more high-protein clover was present. In both years, nitrogen reduced the protein content appreciably because it reduced the amount of clover. Where nitrogen Table 13. Effect of Continuing Fertilizer Treatments on Yield and on Amount of Crude Protein in Forage (Napa County, Marshall Ranch) Yield (lb. per acre) of forage (dry weight) Annual fertilizer treatment (lb. /acre) 1954 1955 Grass Legume Both Grass Legume Both None 1,600 2,333 3,598 4,839 1,670 3,606 1,047 2,693 3,270 5,939 4,645 7,532 1,592 3,361 2,839 4,380 904 3,482 184 2,087 2,496 26P (60 P205) 6,843 3,023 100N 100N,26P 6,467 Per cent of crude protein in forage None 14.8 15.9 14.8 15.3 22.8 22.1 22.7 23.8 18.3 19.7 16.5 18.3 13.8 14.9 13.6 14.5 22.7 23.9 22.2 24.1 16.9 26P (60 P205) 19.4 100N 14.1 100N.26P 17.6 [21] alone had been used for two seasons, clover was almost eliminated, and pro- tein content of the whole forage was ap- preciably reduced. Both grasses and legumes showed in- creased phosphorus following its applica- tion at all phosphorus-deficient locations. The increase was probably of little sig- nificance to grazing animals, however, be- cause the total percentage of phosphorus in the unfertilized forage was generally well above critical levels for animal re- quirements established by the National Research Council (Burroughs, 1958). Except where phosphorus was acutely deficient, unfertilized grass tended to have a higher percentage of phosphorus than did associated legumes. In the Sacramento test (table 14), nitro- gen alone or with phosphorus had little effect on the phosphorus content of either grasses or legumes. Phosphorus treat- ments increased the phosphorus content — more so in the grass than in the legume fraction. Table 14. Effect of Nitrogen and Phos phorus Fertilizer on Phosphorus in Pasture Forage (Sacramento County, Lewis Ranch) Year and Phosphorus in pasture forage treatment (lb. / acre) Grass Legume per cent per cent 1957: None 0.23 0.23 200N 0.24 0.23 200N,35P.... 0.30 0.27 35P 0.31 0.28 1958: None 0.24 0.23 180N 0.23 0.21 180N, 70P.... 0.35 0.30 70P 0.37 0.30 1959: None 0.27 0.26 100N 0.23 0.23 100N, 140P... 0.44 0.36 140P 0.45 0.37 FERTILIZATION MAY CHANGE NUTRIENT UPTAKE BY PASTURE PLANTS The amounts of nitrogen and phosphorus taken up by pasture plants are related to the supply of those nutrients in the soil and to fertilization practices. Calculations of actual amounts of nitrogen and phos- phorus in the harvested pasture forage show how fertilization may change the nitrogen and phosphorus uptake of the pasture community. How nitrogen fertilization alters nitrogen recovery on high-phosphorus soils Nitrogen rate studies at Davis, on a soil considered to have adequate phosphorus, showed the effect of nitrogen on nitrogen recovery by Ladino, orchardgrass, and a mixture of the two species (Peterson and Bendixen, 1961). Table 15 shows nitro- gen uptake by grass and clover in the second year of identical ammonium sul- fate treatments. Yields of a pure stand of orchardgrass were about quadrupled by 160 pounds of nitrogen applied at intervals throughout the season. Nitrogen supplied by the soil to the unfertilized plants amounted to 27.1 pounds per acre. Extra nitrogen re- covered in the harvest of fertilized grass was 92.4 pounds from 160 pounds of fertilizer nitrogen, or 58 per cent of the amount applied. Ladino clover in pure stand yielded 318 pounds of nitrogen in the harvested crop for the entire season. This amounts to 290 pounds of nitrogen fixed per acre if allowance is made for the nitrogen- supplying power of the soil as measured [22 -Q C Q. 3 c O — ir> I® J? ■£ X O **■ 5 — afa e-d .£ .2 = > P I ° o g> t3 a. D -s i c o u (D fc S& I e • cj © oo ■ 6- CD IO • W H f PI G R is S2 1 rH iH . o o o fc fc IZi <5 « fl S 5 e* • IO CO ^ ■ H H N • CM CM "<* • rH CO tD CM CM • CO rH t- • o! O rl ,c» • CO t> OS • rH 1 CM '3 a £ 1 1 o--s 1 H tO t- W CO 00 00 00 rH 00 O "^ o e« t* OO 00 0) t> 00 Q T}< rH rH ^ -tf CM CM CN O H "~"^ N » O H IO CO W M CM CM CN CN £ rH CO CO CO CO £ i a> O CO 00 00 o O "^ CM CM Pi o fl 3 c$ t- 00 Q ^ rH rH ^ "^ CM rH CM -^ fc «? ^~7 t> CM O 00 ■M J £ CO CO CO CO y-i y-t rH o 4» 4 n h «o t- n rH T*l O CM to s c8 e* c— oo oo fl 00 IO OS !> ^ o oo o CJCiOH CO CO I* 't "^ CM CM CM o otf tJ< CO t> S a V CM CM CM CM CO CO ^sf ^ CO CO CO CO Sfc 0. °<4-l Oo T1 **" 4> N N H ^i o ia cm o rH t> IO rH ^ £ a © ffl t- H © CO CO CO co t> io cr> CO rH O rH •2 1 * O rH CO CO CO CN C- rH £ H N CO ^ oo oo oo oo t- t- t- t> fc"? a> si o o o o o 00 CO CD 00 CM CO o o o o 00 CO CO Is JQ rH tH i-\ rH y-{ rH C A O M w u M 3 > CO & J2 H bo •a o TJ 1 o § O o G qi M o H o by nitrogen uptake of unfertilized grass. Additions of nitrogen to Ladino clover grown alone caused only very slight in- creases in the percentage of nitrogen or in nitrogen uptake per acre. Nitrogen ap- plied at 160 pounds per acre increased the amount of nitrogen in the harvested forage by 26 pounds — an apparent re- covery of 17 per cent. Either the applied nitrogen was not used by the clover, and was therefore lost, or the clover did not fix as much nitrogen as it did when un- fertilized. Nitrogen on the mixed legume-grass stand at Davis in the second year of the same experiment had encouraged the grass growth. This change in plant popu- lation reduced the ability of the pasture community to fix nitrogen, since clovers had been greatly reduced. Nitrogen up- take data from this test show a substantial reduction in the amount of clover nitrogen found in the harvest of the mixed plant- ing. The percentage of nitrogen in these clover plants remained the same, but the yield was less. The amount of nitrogen harvested in the grass increased since the yield of grass was up. The total amount of nitrogen harvested in the grass-legume mixture fertilized with 80, 120, or 160 pounds of nitrogen per acre was no greater than that produced in the unfer- tilized plots. It seems clear that any gains in uptake of nitrogen by grass was offset by a reduction in the amount of clover nitrogen. How nitrogen and phosphorus alter nitrogen recovery on phosphorus-deficient soils When soil phosphorus is deficient, fer- tilization with this nutrient over a period of time may greatly alter the nitrogen re- covery of the pasture community if re- sponsive legumes are present. As already shown, nitrogen treatments remain im- portant because they may alter the pro- portion of plant species present in the pasture mixture. Napa County Tests. Nitrogen uptake by the individual species and by the whole forage, for the two-year test period, is shown in table 16. In the first year, the [ nitrogen harvested in phosphorus-treated whole forage was double that in forage from the unfertilized area. Most of this extra nitrogen was found in the legume fraction, but an appreciable amount was also harvested in the associated grasses. Straight nitrogen treatments reduced the amount of legume nitrogen harvested, but did increase the amount of grass nitro- gen for an over-all apparent recovery of 24 per cent of the fertilizer nitrogen ap- plied. By the second season, straight nitrogen treatments had nearly eliminated legumes and thereby reduced nitrogen fixation to such an extent that the amount of nitro- gen recovered was no more than that in the check plot. Phosphorus treatments, on the other hand, increased nitrogen uptake at har- vest in both the legume and grass por- tions of the forage in both seasons. Nitrogen uptake from the nitrogen- phosphorus treatments in the second year was somewhat less than in the area where only phosphorus had been applied. Sacramento Test. Effects of fertiliza- tion upon nitrogen fixation and recovery are summarized, for a three-year period, in table 16. The effect of the first year's nitrogen application was a definite gain in total nitrogen harvested, since grasses were stimulated and clovers little af- fected. The over-all recovery of fertilizer nitrogen was about 33 per cent. When 35 pounds of phosphorus (80 P2Os) were ap- plied alone or in combination with nitro- gen there was an increase in nitrogen up- take amounting to approximately 64 pounds, mostly in the legume fraction. Results of the second year of this test showed that applications of nitrogen very greatly reduced the total amount fixed by the smaller legume population while in- creasing the nitrogen uptake of the grasses. For the community as a whole, the apparent nitrogen recovery was re- duced to 7 to 8 per cent of that applied. At the same time, applications of phosphorus resulted in an increase in nitrogen uptake amounting to about 100 pounds of nitro- gen per acre for the entire season. 24] -a c O 0 Q. c O *5 c c o u u D •o 2 >» : to * a* to S* • Pm 15 |z; ■to** • to fc fc . pm fc fc Ph £ fc O T3 CO © tP CM © to CO CO CO 00 "^ tH 00 00 t> O "* e3 rj* tJ* CO d , t> CM CM O T-l TH CM CM JO T-i T-i O TH T-l T-l T-l TH T-l ii -C 0) u t» H ffl t» 00 CO Tf tH t-MIOH CO t- t< ^ IO N O OJ "o o3 00* CO CM © t> CO* 00 00 CM t-* d ^* d t- 01 00 0 M . Oi t- (N (N CO t-I CO 00 U) H N 00 H CM N (N CO CO t> 00 £ H H N CM t-I tH CM tH CM rH CM t-i CO .s e 3 cd © os oo © co oo o to to ^ W T}i H t-I t> CO CM tH t> tH O 04 s 3 p o3 © oo* d cm OHMO d co «a* O* CM 00 ^ 00 cm' co d t» CO Tf O d t» . 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Eighty additional pounds of nitrogen in 40-pound increments were applied in July and September. The pas- tures were primarily of dallisgrass with some Ladino clover and trefoil present. The clipping tests referred to in table 21 were carried out in a fenced exclosure in one of the untreated fields of the graz- ing trial. The experimental fields were stocked with yearling steers at rates of 2.7 animals per acre on the unfertilized fields and 4.08 per acre on the fertilized. The fields were grazed on a rotation basis, with animals on each field 7 days, followed by 14 days allowed for recovery. The fertilized fields gave a beef pro- duction of 602 pounds per acre as com- pared with 324 pounds on the nonferti- lized field (table 24). Animals in the fer- tilized fields gained at a slightly higher rate per day. The beef gains — evaluated at 18 cents per pound — gave a grazing income of $108 per acre on the fertilized fields, as compared with only $58 per acre on the control fields. The profit per acre from fertilization, after deducting cost of material applied, amounted to $23.11. It will be noted in the clipping test (table 22) that 150 pounds of nitrogen per acre almost doubled grass yields — from 3,995 pounds per acre to 7,813 pounds. Similarly, beef gains were almost doubled — from 324 to 600 pounds. The additional 288 pounds of beef attributable to 145 pounds of nitrogen are equivalent to 1.98 pounds of beef per pound of nitrogen applied. Grazing and clipping tests in Merced County were also carried out in 1956 on dallisgrass pasture on a heavy clay soil with some alkali spots present to find out whether fertilization with nitrogen and phosphorus might be feasible. Both trefoil and Ladino were present, but grew poorly. Most of the forage production in the summer months was from dallisgrass in the better areas and from bermudagrass around the alkali spots. The following results show that drv- weight forage yields were much higher with nitrogen plus phosphorus than with nitrogen alone. [33] FERTILIZER YIELD OF FORAGE Ib./acre Ib./acre None I,438 170 N 2,125 170 N + 15 P (35 P205) 3,412 Two fields (one of which was fertilized with nitrogen and phosphorus) with ac- cess to water were selected for the graz- ing test. Each was divided by cross fences into three smaller fields which were grazed on a rotation basis. The first year's results showed beef production almost doubled on the fertilized fields. With beef evaluated at 18 cents per pound, and ni- trogen costing 15 cents per pound, the operation scarcely broke even (table 25). In the second season, anhydrous am- monia, a lower priced source of nitrogen, was applied at low concentration in the irrigation water during the summer, fol- lowing a spring treatment with (16-20-0). The lower-cost nitrogen, plus higher- priced beef, returned a profit of $27.63. With low-cost nitrogen, fertilization of dallisgrass pastures appears economically feasible at this location. Some hay or barley supplement was required to maintain daily gains of cattle at desired levels on pasture of this type. Fertilized Coastal Bermudagrass Showed High Nitrogen Recovery Results from a demonstration on fer- tilized coastal bermudagrass in Kings County show a large increase in growth as a result of frequent but low nitrogen applications (table 26). In this test, 150 pounds of nitrogen per acre, applied in five 30-pound increments, gave a yield increase of approximately 3Mi tons for a fertilizer cost of only $8 per extra ton if the nitrogen was figured at 12 cents per pound. The additional nitrogen harvested from the forage amounted to 134 per cent of the amount applied. This apparent re- covery implies that fertilized grasses have the ability to forage more deeply and to "mine" nitrogen and exploit more soil than do unfertilized grasses. The economics of fertilizing a pasture of this type is quite encouraging because the extra forage is probably worth considerably more than the nitrogen required to produce it. With forage at $15 per ton, the point of maxi- Table 24. Results of Irrigated Pasture Fertilization* on the Basis of Cattle Gains (Madera County, May 8 to September 26, 1 956) Factor Unfertilized Fertilized pasture pasture 70 50 2.70 4.08 494 lb. 480 lb. 617 lb. 640 lb. 103 to 141 103 to 141 123 lb. 160 lb. 0.93 1b. 1.18 1b. 324 lb. 602 lb. $ 58.34 $108.36 $ 50.02 $ 26.20 $ 00.71 $ 23.11 Number of acres Average number of yearling steers per acre Average weight of steers at start of test Average weight of steers at end of test Days pastured Average total gain per head Average daily gain per head Average production of beef per acre Value of beef produced per acre at 18 cents /lb Value of additional beef produced per acre Cost of fertilizer applied per acre Interest per acre on fertilizer investment at 6 per cent Profit per acre from f ertilization * Fertilizer applied: May 2, 1956: 200 lb. 20-20-0 per acre. 100 lb. ammonium sulfate per acre. July 6, 1956: 200 lb. ammonium sulfate per acre. [34] mum profit would be about 200 pounds of nitrogen per acre. It should also be noted that the protein content of the forage was increased with each added increment of nitrogen. How- ever, probably no real advantage in for- age quality would result from the higher rates of nitrogen. Table 25. Results of Irrigated Pasture Fertilization* on the Basis of Cattle Gains (Merced County, 1956 and 1957) Factor 1956 129 days (5/28-10/4) Untreated pasture Fertilized pasture 1957 162 days (4/9-9/18) Untreated pasture Fertilized pasture Stocking rate (average animals per acre) Average daily gain (lb.) Production of beef per acre (lb.) Increase due to fertilizer (lb.) Value of beef per pound Value of beef per acre Cost of hay fed Value of extra pasture per acre Total grazing income per acre Cost of fertilizer Profit or loss from fertilization 1.45 1.02 194 $00.18 $35.00 $00.50 $35.00 2.30 1.08 322 128 $00.18 $58.00 $ 1.50 $ 6.00 $64.00 $29.50 -$00.50 1.45 1.11 261 $00.20.5 $53.50 $ 1.00 $ 3.80 $57.30 2.30 1.20 446 185 $ 00.20.5 $ 91.43 $ 1.50 $ 18.00 $109.43 $ 24.50 $ 27.14 Fertilizer applied (1956) May Nto + Pis from (20-10-0) July N4o urea August Neo urea Total Nito + 15P (35 P2O5) Fertilizer applied (1957) March N40 + P22 from (16-20-0) Summer Nn5 from NH3 in 10 irrigations Total N155 + 22 P'(50 P2Os) Table 26. Effect of Fertilization on Yield, Quality, and Cost of Coastal Bermudagrass Pasture Forage (Kings County, 1962, six cuttings) Fertilizer applications (lb. per acre) Yield (dry wt.) Fertilizer cost Fertilizer cost per extra ton forage Crude protein Nitrogen recovery In forage As per cent of N applied None 30 X 5 = 150 N... 60 X 5 = 300 N.... 120 X 5 = 600 N... tons /acre 4.25 7.58 7.98 9.25 $26.50 46.75 87.25 $ 7.96 12.53 17.45 per cent 11.9 15.5 16.6 18.6 lb. /acre 163 361 420 549 134 87 65 [35] ACKNOWLEDGMENTS The authors express their appreciation to the following University of California Farm Advisors who conducted the field trials reported herein: Lester E. Allen (Las- sen); Thomas E. Bedell (Modoc); Glenn Eidman (Glenn); Walter E. Emrick (Madera) Herbert S. Etchegaray (Kings); Glenn S. Goble (Sacramento) ; D. Irving Grover (Napa) W. B. Hight (Madera); Walter H. Johnson (Placer); McKinley V. Maxwell (Siskiyou) Don A. Petersen (Merced); Carl W. Rimbey (Plumas); Carl A. Schoner, Jr. (Yolo) Arthur K. Swenerton (Solano); Seymour W. Thurber (Shasta). LITERATURE CITED Bedell, Thomas E. 1962. Results of nine years of meadow fertilization in Modoc County. University of California Agr. Ext. Service. (Mimeo.) Burroughs, Wise 1958. Nutrient requirements of domestic animals: IV. Nutrient requirements of beef cattle. Washington, D.C. National Research Council — National Academy of Sciences Publication 579. Martin, W. E. 1958. Sulfur deficiency widespread in California soils. California Agriculture 12(11): 10-12. McCollam, M. E. 1948. Why use potash on pastures? Better crops with plant food. American Potash Institute, Washington, D.C. Olsen, S. R. 1954. Estimation of available phosphorus in soils extracted with sodium bicarbonate. Washington, D.C, U. S. Dept. Agr. Cir. 939. Peterson, M. L., and L. E. Bendixen 1961. Plant competition in relation to nitrogen economy. Agronomy Journal 53: 45-48. Rendig, V. V., W. E. Martin, and F. F. Smith 1950. Effect of fertilizers on composition of forage on phosphorus-deficient soils. California Agriculture 4(8): 6-12. Ulrich, Alrert 1940. Progress report of field experiment conducted at Oakdale with Ladino clover on San Joaquin loam. Fertilizer Studies by Division of Plant Nutrition, Uni- versity of California. (Mimeo.) Willhite, Forrest M., H. K. Rouse, and D. E. Miller 1955. High altitude meadows in Colorado: III. The effect of nitrogen fertilization on crude protein production. Agronomy Journal 47:117-21. 1.-.///-7. (if, (Klf.l I )L.L.