Effects of wide-narrow row planting on the physi-chemical properties of black soil and maize yield

Wide-narrow row planting (WP) has been widely used to increase the planting intensity per unit area for the high yield of grain. However, the consumption of soil fertility can dominate the sustainable utilization of black soil. This study aims to clarify the effects of the wide-narrow row planting on the black soil structure and organic carbon/nitrogen. Three farmlands with different years of wide-narrow row planting (three years WP3, seven years WP7, ten years WP10) were sampled in Fan Rong Town, western Heilongjiang Province, China. The planting with equal row spacing (three years-EP3, seven years-EP7, and ten years-EP10) is the control. The soil aggregate structure was characterized to measure the variation in the soil carbon pool. The results show that: The soil organic carbon and total nitrogen decreased by 1.20 and 0.20 g/kg (P<0.05), respectively, compared with the EP treatment, whereas, the aggregate organic carbon decreased by 0.87 g/kg under WP3 treatment. The soil organic carbon increased by 1.26 g/kg with the extension of planting years. The total nitrogen shared no significant difference. The aggregate organic carbon increased by 2.00 g/kg after 10 years of wide-narrow row planting. There was a significant increase in the percentage of the soil macro-aggregate (>0.25 mm), mean weight diameter (MWD), and corn above-ground biomass under wide-narrow row planting. The geometric mean diameter (GMD) failed to improve under short-term wide-narrow row planting (WP3) treatment. However, the GMD value increased significantly with the extension of planting years to 10 years. The WP3 treatment increased the content of soil macro-aggregate by 10.5%, MWD by 10.3%, GMD by 9.3%, and above-ground biomass by 9.1%, compared with the EP3. The percentage of soil macro-aggregates increased by 18.6%, MWD by 13.1%, GMD by 19.9%, and above-ground biomass by 15.9% after 10 years of wide-narrow row planting. A decreasing and then increasing trend was found in the effect of wide-narrow row planting on the soil particulate organic carbon content (POC). The POC of the WP3 treatment (planted in the wide and narrow rows in the 0-20 cm soil layer for three years) was found to be 21.92% lower than that of the EP3 treatment, which was planted with equal row spacing. The WP7 treatment exhibited a 9.96% reduction, compared with the EP7 treatment (after 7 years of wide-narrow row planting). While the WP10 treatment demonstrated a 12.04% enhancement relative to the EP10 treatment (after 10 years of wide-narrow row planting). Soil mineral-associated organic carbon content decreased significantly after 3 years of wide-narrow row planting. There was no significant difference in the mineral-associated organic carbon content, as the planting period of wide-narrow row planting was extended to 7 and 10 years. The soil organic carbon content gradually changed from a negative to a positive effect after wide-narrow row planting. The root and above-ground biomass were attributed to the plant-derived carbon input. The negative effect was gradually offset by the increase in planting intensity and the accumulation of time. In conclusion, wide-narrow row planting can greatly contribute to the soil carbon pool in black soil over time, thereby improving the soil structure and quality.