تأثیر رطوبت خاک و عمق شخم بر عملکرد گاو آهن بشقابی در یک خاک لوم رسی

The effects of three levels of soil moisture content (10 - 12, 13 - 15 and 16 - 18% d.b.) and three levels of plowing depth (15, 20 and 25 cm) on draft, specific draft, and drawbar power requirements of a 3 - bottom disk plow and on soil pulverization and inversion in a clay loam soil were investigated. The experimental design was a randomized complete block design with a 3 × 3 factorial. Except in soil inversion, the effect of soil moisture on all of the performance parameters mentioned, was highly significant. Mean values of draft, specific draft and drawbar power requirements and clod mean weight diameter were minimized at 13 - 15% and 16 - 18% soil moisture contents, respectively. The effect of plowing depth was highly significant only on draft and drawbar power requirement of disk plow, in such a way that the mean values of these two parameters were significantly increased with plowing depth, while specific draft showed only a mild decreasing trend. In order to provide a quantitative index to express the degree of soil pulverization by tillage implements, a tractor-pulled rotary sieve was designed and fabricated. With this apparatus, in-field determination of soil clod mean weight diameter (MWD) following plowing was possible. The results showed that the effect of soil moisture content on MWD was highly significant, such that, plowing at 10-12% moisture content produced the largest clods, whereas the effect of plowing depth on MWD was not significant. The decreasing trend of MWD with soil moisture content persisted to the highest moisture level studied (16 - 18%), in which the average clod MWD (33.8 mm) was about 72% smaller than those formed at 10-12% moisture content. The effects of plowing depth and soil m. c. on soil inversion by disk plow were not significant and the overall soil inversion was about 54% which was in agreement with those reported by other researchers.