I ■3-1 "73 Legume Damage By Tractors ■^^ '^ / By Gordon L. Byers and Robert F. Lncey Station Bulletin 473 April 1962 AGRICULTURAL EXPERIMENT STATION UNIVERSITY OF NEW HAMPSHIRE DURHAM, NEW HAMPSHIRE 3^1 ^73 Legume Damage By Tractors (Tordoii L. Byers and Robert F. Liicey Station Bulletin 473 April 1962 AGRICULTURAL EXPERIMENT STATION UNIVERSITY OF NEW HAMPSHIRE Dl RHAM, NEW HAMPSHIRE SUMMARY A study was made to evaluate the effect of tractor traffic on yields of alfalfa and red clover. Eight hasic treatments were applied hy using two tractors, one with new tires and one with smooth tires. The tests were conducted on a Paxton loam soil. Plots were seeded in August of 1959 and 1960. The following spring the first crop was harvested by hand. The traffic treatments were applied to the second growth when the plants were approxi- mately four inches high. The area between the tractor tracks was kept cleanly mown, consequently, only those plants which had been run over by the tractor were allowed to grow. Results show that tractor traffic does injure and kill young plants. A smooth tire does more damage than a new tire. Stem, leaf and crown damage was prevalent following all treatments. This research was supported in part by funds from regional project NE-13. The Mechanization of Forage Crops, Harvesting, Processing, Storing and Feeding, a cooperative study, including Agricultural Experiment Sta- tions in the Northeastern Region, of the United States Department of Agriculture. The authors wish to express their appreciation to Richard D. Merritt and John P. Adams, University of New Hampshire photographers, for their asssitance in taking and preparing the pictures in this bulletin. The contribution of R. H. Kilpatrick, Plant Pathologist and Merle Ct. Wright, technical assistant, is gratefully acknowledged. Cover Ph(»t4»: Effect of increasing drawbar pull on alfalfa and red clover plants — center plants arc from the control plot — degree of pull increases from center to left and right. Legume Damage by Tractors by (iordon L. Bvers and Robert F. Lucev* Mo(l(Mn farming necessitates moving tractors and equipment over fields where plants are in various stages of growth. In- corporated in modern farming methods has been the trend towards employing more tractors with greater power at the drawhar. Increased drawhar horsepower was obtained without increasing the overall weight of the tractor. Heavier loads are being pulled by the tractor now that tractors have the ability to do so. As a result, tractor drive wheel slippage, in the normal process of operations, has in- creased. Tractor tire treads have been designed to provide adequate traction along with roadaljility. Little or no attention lias ])een given to the effect that weight, area of contact, or slippage may have on yields of alfalfa or other legumes. Barger and Roberts ( 1 ) found that larger drawhar pull was obtained on green grass because of the ability of new tires to cut or shave off the grass and reach firm ground. Worn tires which had greater contact area, slipped on the grass after it had been matted down. The studies reported in this bulletin were concerned with the extent of damage inflicted on alfalfa and red clover plants by ( 1 ) increasing drawbar pull and ( 2 1 increasing the area of contact between the tire and the ground. Increasing the draw- har pull increases the ground pressures under the rear wheels by transferring weight from the front of the tractor to the rear of the tractor. Drive wheel slippage also increases as the draw- bar load increases. Increasing the area of ground contacted by the tire exposes more plants to damage. Tractor tires that ai"e badly worn have a larger contact area than tires with new tread. Materials and Methods A paxton loam soil located in Northwood Ridge. Northwood. New Hampshire, was used in this study. Soil test results showed that the soil was strongly acid and low" in available plant nu- trients. * Associate Agricultural Engineer and former Assistant Agronomist, re- spectively, in the Agricultural Experiment Station. 3 Figure 1. Plots of Alfalfa and Red Clover on which 1960 trials were conducted. Picture taken May 27, 1960. To reduce the acidity and to correct for nutrient deficiencies, lime and fertilizer were applied on the hasis of soil test re- sults. Four plots each, of Narragansett alfalfa ( 14 pounds per acre) and Peiniscott red clover (eight pounds per acre), were seeded on July 28, 1958, and August 1, 1959. An 11x7 grain drill fitted with hand seeding tul)es was used to place the seed above the ])atid of 8-16-16 fertilizer which was applied at the rate of 200 i)ounds per acre. In the spring, and after the first crop was removed, 150 pounds per acre of muriate of potash (60% K.O) was applied. (Figure 1). Spring growth produced hy the plants which became estab- lished the preceding summer and fall was harvested on June, 1959, and June, 1960. A National sickle bar type mower was used to cut the herbage. The cut herbage was removed by mamial labor. The jdants were allowed to recover to a height of four inches before the basic tractor traffic treatments were applied. Eight basic treatments were applied, using a tractor with new tires and a tractor with old, smooth tires. Four different draw- 4 I)ar loads — namely: 0 Ihs.. 650 Ihs., 1250 ll)s., 1800 Ihs., with the new tires; and 0 Ih.. 500 lbs., 1100 lbs., 1500 lbs., with the smooth tires — (effected a ranjre of wbeel slipjjago and weight transf<'r. A mower operatinji, iin -^' "> '■' ;,■..%/..: JL. > Figure 2. Areas between treated plots were kept cleanly mown during the growing season. Tall row left center is a coMlr«>l row. the two rows to the rifjhl show retarding i'(T«'«'t of smooth tires with I5UU Ihs. - UJ < IT UJ 20 > < 10 - 5M 00 FH T RE S 80 70 SO- SO 40 30 - 20 10 I i I NEW TIRES I I- i I I I i I i i i I p m r l^. 4 ; CONTROL 0 500 1100 1500 DRAWBAR PULL IN Figure 6. Effect of increasing drawbar new tires on vieids of red clo CONTROL 0 650 1250 1800 POUNDS pull with smooth tires and ver (1960). drive wheel slippage did not result in a significant decrease in yield over that already inflicted by the effect of tractor weight alone. Figure 4 shows the effect of traffic on red clover. Significant damage was inflicted hy smooth tires, the degree of damage increasing as the drawliar load increased. With new tires, how- ever, although some damage was inflicted, the degree of dam- age was not as pronounced as it was with old tires. This sug- gests that the greater area of contact with the smooth tires was a factor. As a rcsiiJt ot cxprriiMicc" gained from the 1939 >tiMlio. Iirttcr plots (Figure 1) \ver<' estal)lishe(l and plant eoiinting and har- vesting technicjues improved in 1960. Conseipiently the authors feel that the I960 results are very indieative of what ean he expeeted in the way of legume damage by traetor tralTic. / % Figurr 7. Examples of alfalfa and red clover plant damage. >ole erushed and twisted stems, bruised and lacerated leaves. In 1960. as in 1959. l)oth sett* of tires inflicted significant dam- age when compared to the control plots. On hoth alfalfa and red clover the smooth tires inflicted more damage than the new tires. The major very possible that damage inflicted by field traffic to jilant^ mav be a contributing factor to a reduction in a stand of legumes. 11 Figure 9. Red clover root crown damage, (top) whole crown and (bottom) roots sliced longitudinally. Left to right, control — new tire — smooth tire — bottom 4th root, smooth tire. 12 CONCLUSIONS 1. Significant damage was* inflicted on alfalfa and red clover plants when they were subjected to tractor traffic. 2. Increasing the area of tire contact, increased the number of plants damaged. .'5. Slippage of the drive wheel is not as important a factor as weight. The two combined, however, inflict more damage tban weight alone. 4. Minimum pressures to elminate damage are well Iielow average tractor tire contact pressures. 5. Damaged plants continue to grow, hut at a slower rate and yield much lower than undamaged plants. 6. Plant crowns are severely damaged and may he more sus- ceptible to disease. 7. Field traffic, where j)lants will be damaged, should be re- duced to a mininuim. 13 LITERATLIRE CITED BaR(;ek. E. L. and J. Roberts. Effect of Tire U em on Tnntor Perfnrm- (inre. Agricultural Enaineering, Mav 1^)3Q. 14