Inter-annual variations of seed cotton yield in relation to soil organic carbon and harvest index in reclaimed desertified land

Abstract Understanding the biophysical mechanisms responsible for changes in crop productivity is critical for the conservation and sustainable development of the reclaimed desertified land. Here, a long-term experiment of monitoring the soil and growth of high-profit cotton crop with three rates of fertilizer was initiated in 2004 and a two-year experimental manipulation of fertilizer was conducted in 2018 and 2019 in Xinjiang, China. The data for soil attributes, seed cotton yield (SCY), and yield components were collected every year in the long-term experiment, and canopy ecophysiological traits were measured in the two-year experiment. Path analysis indicated that inter-annual variations of SCY were primarily related to the aboveground biomass (AGB), harvest index (HI), and the number of bolls per plant (NOB), with the relative importance in the order of AGB≈HI > NOB. Higher leaf nitrogen content and leaf photosynthesis capacity in the early-growth stage promoted the canopy area expansion and AGB. Soil organic carbon (SOC) in fields where the fertilization has been well managed had an “increase-decline-rebound” tendency, with an increased accumulation during the first 4–5 years. A quantitative “rise to the max” curve between AGB and SOC was observed, showing a steep increase in AGB with increasing SOC at a low level of less than 6.0 g kg−1. Positive relationships among soil nitrogen (N), phosphorus (P) accrual, and SOC were found, suggesting that SOC enrichments in the newly reclaimed desertified land increased the soil’s capacity to preserve nutrients and contributed to the increase in cotton AGB.