JWSS - Journal of Water and Soil Science

Soil erosion by water is a serious environmental problem, particularly in semi-arid regions. In these areas, water loss strongly affects soil loss as well as soil productivity in the rainfed lands. Determination of appropriate seed density for each tillage direction is vital to achieve high crop yield and to prevent soil and water losses. This study was conducted to investigate the combined effects of tillage direction and plant density on the soil and water losses in a rainfed land. Twelve crop plots with the dimensions of 1.5 m × 5 m were installed to investigate the effect of two tillage directions (up to the down slope and on the contour line), two seed densities (90 and 120 kg h^-1), a three replications in a rainfed land with 10% slope steepness. Soil and water losses were measured in each plot during the wheat growth period (from October 2015 to June 2016). Significant differences were found between both tillage direction and plant density in the runoff (P<0.05) and soil loss (P< 0.001). Runoff and soil loss in the up to down slope tillage was 4.16 and 4.08 times bigger than the contour line tillage, respectively. Runoff and soil loss with the seed density of 120 kg h^-1­ ­­were 11.25 and 26.32% lower than those with 120 kg h^-1­, respectively. This result was associated with the increased cover crop and its control on water flow and the enhancement of water retention in the soil. There was no significant interaction between tillage direction and plant density in the runoff and soil loss. The importance of tillage direction in the soil and water loss was very larger than that of the plant density. The application of 120 kg ha^-1 seed density on the contour line could, therefore,   considerably prevent soil and water losses in the rainfed lands.

Limited information is available on the effect of residues rates and slope direction on dryland wheat
(Triticum aestivum L.) yield.  This study was carried out to determine the effects of residues rates and tillage direction on grain yield and yield components of the Sardary wheat in a dryland region in Zanjan. Five wheat residues rates (0, 25, 50, 75 and 100% surface cover) were applied and incorporated into soil in two slope directions (along the slope and on contour lines) using the randomized complete blocks design with three replications in a land with 10% slope steepness. Overall, thirty plots with 2m × 5 m dimensions were installed in the field and wheat grain yield and yield components were determined for growth period from 2015-2016. Results indicated that grain yield and yield components were significantly affected by the residues rates and slope direction and their interaction. In contour tilled plots, wheat grain yield (1.78 to per hectare), thousand grain weight (42.26 kg) and wheat height (55.11 cm) were 5.32, 5.01, 16.19 and 1.36 percent more than the plots tilled along the slope. The highest grain yield was found in 75% of residue (2.45 ton per hectare) under contour line direction which was about 53% bigger than control treatment (0% straw mulch) under along the slope. This study indicated that the application of straw mulch before cultivation and incorporating into soil using contour line tillage are proper soil management methods to obtain higher wheat yield in this dryland region.