关键词: 稻油轮作, 镁肥, 产量, 镁积累量, 土壤镁平衡

Abstract:

【Objective】To address the critical constraint of soil available magnesium (Mg) deficiency on annual productivity in the rice-rapeseed rotation systems of China’s Yangtze River Basin, this study systematically investigated the effects of Mg fertilizer application rates on annual crop yield formation, nutrient uptake, and Mg balance in the soil-crop system, for providing a theoretical basis for efficient Mg management in rotation systems.【Method】Based on a field experiment initiated in 2017 at Wuxue, Hubei Province, this study selected six rotation cycles (2017-2023) with five Mg fertilizer treatments (0, 15, 30, 45, and 60 kg MgO·hm^-2 per season). The crop yield components, nutrient concentrations in different plant parts, and biomass in the rice-rapeseed rotation system were measured. Based on these measurements, crop nutrient accumulation, fertilizer use efficiency, and soil nutrient balance were calculated to clarify the magnesium requirement characteristics of crops in the rotation system and establish fertilization strategies for the rotation system.【Result】(1) Mg application significantly increased annual system productivity, with yield increments of 9.5%-23.8% for rapeseed and 2.2%-4.0% for rice. A linear-plateau model indicated the maximum yields of 2 388 kg·hm^-2 (rapeseed) and 8306 kg·hm^-2 (rice) at an annual MgO rate of 60.4 kg·hm^-2 (38.1 kg·hm^-2 for rapeseed season; 22.3 kg·hm^-2 for rice season). Yield improvements in rapeseed were attributed to increased siliques per plant and seeds per pod, while rice yield gains resulted from higher effective panicles and filled grains per panicle. (2) Mg application significantly elevated Mg concentrations in all plant parts at maturity, with smaller effects on grains. The maximum increases were 45.1% (rapeseed stem), 66.2% (pod wall), and 8.5% (seed) for rapeseed, and 14.9% (stem and leaf) and 6.5% (seed) for rice. Annual biomass and Mg accumulation increased by up to 1 820 kg·hm^-2 (8.5%) and 6.3 kg·hm^-2 (29.5%), respectively. While rice showed higher absolute biomass and Mg accumulation, rapeseed 's proportional contribution to annual Mg uptake increased with Mg application. (3) Mg fertilizer apparent utilization rate and agronomic efficiency declined with increasing application rates, with rapeseed consistently exhibiting higher utilization than rice under equivalent Mg inputs. Mg removal by crops exceeded fertilizer input below 90 kg·hm^-2 annual application, while 120 kg·hm^-2 resulted in Mg surplus. If the straw was returned to the field, Mg surplus would occur when the annual Mg fertilizer application rate was 60 kg·hm^-2.【Conclusion】The application of Mg fertilizer significantly enhanced annual crop productivity in the rice-rapeseed rotation system, with rapeseed exhibiting more pronounced demand and utilization advantages for Mg. It was recommended that the annual Mg fertilizer application rate in the rotation system be approximately 60 kg·hm^-2, with a seasonal application ratio of about 2:1 between the rapeseed and rice seasons, to achieve efficient Mg fertilizer management and to improve annual productivity.

Key words: rice-rapeseed rotation, magnesium fertilizer, yield, magnesium accumulation, soil magnesium balance