Nitrogen and Phosphorous Loss as Affected by Plough Direction in Rainfed Wheat Land of a Semi- Arid Region

Sloping farmlands are the major sources of soil, water and nutrient losses in arid and semi-arid regions. Information about the impacts of different tillage practices on soil erosion, nutrient loss and crop nutrient uptake on the sloping farmland of semi- arid soil is, however, limited. This study was carried out to investigate the effects of tillage direction on soil, water, nitrogen and phosphorous losses and their uptake by plant in a rainfed wheat land. Field experiments were conducted in two tillage directions: downslope tillage and contour line tillage with four fertilization treatments: control, urea, triple superphosphate, and urea + triple superphosphate at the field plots with 1.75 m ´ 8 m in dimensions by using the randomized completely block design at three replications in Zanjan Township during 2014-2015. According to the results, Significant differences were found between the two tillage practices in soil loss (P < 0.001), water loss (P < 0.001), nitrogen loss soil loss (P < 0.001), and nitrogen uptake by wheat grain (P < 0.001), while phosphorous loss and its uptake did not show any statistically significant difference. Soil and water loss in the downslope tilled plots was 1.65 and 2.50 times higher than the contour line tillage, respectively. Nitrogen loss in the downslope tilled plots was 1.29 times more than that in the contour line tilled plots. Nitrogen loss in the plots was attributed to soil and water loss, so significant relationships were observed between nitrogen loss and soil loss (R2 = 0.59) and water loss (R2 = 0.55). This study, therefore, revealed that the tillage direction is an important factor controlling runoff, soil loss, and nitrogen loss and its uptake by wheat in the rainfed lands of semi-arid regions. Application of the contour tillage is, therefore, the first step to conserve soil and water and to improve soil productivity in these regions.