Cotton stubble mulching helps in the yield improvement of subsequent winter canola (Brassica napus L.) crop

Either canola (Brassica napus L.) or cotton (Gossypium hirsutum L.) production in China ranks the first in the world in planting area and/or output. Three quarters of Chinese canola are grown in Yangtze River Valley and half of cotton planting area is cropped with canola sequentially. Cotton stubble are normally removed from the field or burned in situ before canola sowing to facilitate field management, and potentially to reduce the incidence of diseases. However, the way of cotton stubble disposal is labor costing, resources wasting and/or air pollution contributing. Hence, two-growing-season field experiments were conducted to evaluate the effect of cotton stubble mulch with stalk remaining straight and lying down at elongation stage on canola grain yield, canopy temperature and soil nutrients status. The first experimental treatments were established following a split-plot design of a randomized complete block with cotton stubble mulching (0 and 3250 kg ha−1) as the main plot and canola planting density (22.5, 30.0, and 37.5 plants m−2) as the sub-plot. The results revealed that canola yield under cotton stubble mulching (CSM, 3250 kg ha−1) was 9.9% higher than that under no cotton stubble mulching (NCM, 0 kg ha−1) averaged across two growing seasons, possibly because canola canopy mean daily temperature (MDT) of CSM was 0.5 °C higher than NCM during the winter. Planting density significantly affected canola yield as well, where moderate planting density (30.0 plants m−2) resulted the highest canola yield (2425 kg ha−1). The second experiment was designed to compare soil nutrient content between CSM and NCM, which revealed that soil nutrition, especially alkaline N and available K, was improved by cotton stubble mulching. The results suggest that cotton stubble mulching would be a multi-win alternative choice for cotton stubble disposal and 30.0 plants m−2 should be the optimal density for canola production in the region.