Effect of seed density and row spacing of rainfed wheat on the USLE C-factor in a semi-arid region, Zanjan province

One of the major concerns in the use of the Universal Soil Loss Equation (USLE) in the areas under sever soil erosion rate is the lack of precise data on the cover crop factor (C) for various agricultural crops. Despite in some countries especially the United state, quantitative information are available on the C-factor, there are substantial difference in climatic and pedological conditions with other areas especially semi-arid regions. Rainfed wheat is the major agricultural crops in these areas which would be planted with different density and row spacing in slope farms. There is no information on the effect of seed density and row spacing on the C-factor in rainfed wheat in semi-arid regions.

A field experiment was conducted whit two seed density (90 and 120 kg per hectare) and two row spacing (20 and 25 cm) along with their control plots (without planting seed). The experiment was performed with the blocky randomized design at three replications in a 10% slope land during 2015- 2016. Wheat seeds were sown by drilling set wheat nine and eleven rows for making 25 cm and 20 cm spacing between rows respectively. Eighteen plots with 5 m long and 1.5 width were installed in the farm to measure soil loss under natural rainfalls during from October 2015 to July 2016. The C-factor for each planted plots was determined using the proportion of soil loss in it plot to the same row spacing plot without wheat cultivation. An independent t-test was used to statistical analysis on the effect of seed density and row spacing on the C-factor in the rainfed wheat.

Results indicated that C-factor in 90 and 120 Kg per hectare seed density was 0.42 and 0.43, respectively. The C value between the two seed densities wasn’t statistically significant. Increasing seed density in the planting rows decreased wheat growth due to increasing repetition rate among plants. The C-factor in 9-row seeding with 25 cm row spacing was 0.34, while its value in 11-row seeding was 0.51, showing 33 percentage significant increase in the C value (p <0.05). Decreasing of soil loss as well as the C-factor in 9-row spacing plots was associated with increasing furrow cross section area on one hand, and a little plant repetition occurred between the rows, on the other hand. Thus, soil loss in the cultivated plots was less than the contour plots. Significant difference wasn’t found for interaction between seed density and row spacing. The lowest value of the vegetation cover factor (C) was observed in 9-row seeding (25-cm row spacing) with 120 kg per hectare.

The study indicated that the C-factor in rainfed wheat varies between 0.33 and 0.51. Seed density was not the major factor controlling the C-factor in rainfed wheat, while the row spacing significantly affected on the C-factor in the rainfed lands in the area. The C-factor of wheat can be considerably declined by changing row spacing from 11-row (20-cm row spacing) to 9-row (20-cm row spacing) with 120 kg per hectare seed density in rainfed lands.