Responses of quality components of hybrid indica rice to yield, environment and soil nutrients in southern Sichuan, China

Objectives In southern Sichuan, high temperatures and drought frequently occur during summer, exposing rice plant to heat stress. This results in a decline in seed-setting rate and grain plumpness, leading to generally poor milling quality and appearance quality. We investigated the effects of environmental conditions and soil nutrient status on yield and quality components of hybrid indica rice, aiming to provide cultivation strategies for achieving high yield and superior quality in hot and drought-prone areas of southern Sichuan during summer.

Methods Field experiments were conducted from 2018 to 2020 at seven locations across four prefecture-level cities—Luzhou, Yibin, Neijiang, and Zigong. Two hybrid rice cultivars, ‘Nei 6 You 107’(N6Y107, high-quality type) and ‘Rong 18 You 1015’ (R18Y1015, common type), were used. Four nitrogen application rates for panicle fertilizer were set: 0, 60, 120, and 180 kg/hm², with a no-fertilizer application treatment as the control (CK). Soil samples were collected before transplanting to determine baseline fertility. Grain yield was measured at harvest, and grain samples were taken to assess rice milling quality.

Results 1) Three quality traits—head rice rate, chalky grain rate, and chalkiness degree—were significantly influenced by environmental conditions coefficient of variation (CV) ranging from 28.31% to 58.45%, whereas grain length-to-width ratio, gel consistency, and amylose content were minimally affected (CV ranging from 2.75% to 6.53%). Yield was moderately influenced by environmental conditions (CV of 11.52%). 2) Significant differences (F values ranging from 28.15 to 602.82) were observed in yield, head rice rate, grain length-to-width ratio, chalky grain rate, chalkiness degree, gel consistency, and amylose content across the three years. A highly significant negative correlation (r = −0.4991, n = 56) was found between rice amylose content and nitrogen application rate for grain fertilizer. 3) Rice yield and quality traits, including head rice rate, grain length-to-width ratio, chalky grain rate, chalkiness degree, gel consistency, and amylose content, exhibited highly significant or extremely significant linear relationships with geographical location and soil nutrient background values (F values ranging from 13.98 to 14155.2), with determination coefficients (R²) as high as 89.48% to 99.99%. However, the key factors influencing each quality trait varied across different years and varieties. Overall, over the three years, increasing soil available nitrogen and potassium contents while controlling phosphorus content was beneficial for reducing chalky grain rate and chalkiness degree and increasing amylose content. 4) The correlations between yield and quality traits varied across different years. Combined correlation analysis from 2018 to 2020 revealed highly significant negative correlations (r ranging from −0.1898 to −0.3192, n = 210) between yield and grain length-to-width ratio, gel consistency, and amylose content, and highly significant positive correlations (r ranging from 0.1516 to 0.1661) between yield and chalky grain rate and chalkiness degree. Under the ecological conditions of high temperatures and summer drought in southern Sichuan, the common variety ‘Rong 18 You 1015’ exhibited significantly higher head rice rate and amylose content than ‘Nei 6 You 107’, demonstrating stronger environmental adaptability.

Conclusions Significant interactions among interannual ecological conditions, soil nutrient levels, and cultivar characteristics were observed for rice quality. Higher soil available nitrogen and potassium contents and lower available phosphorus content are conducive to improving rice quality. Increasing nitrogen application for panicle fertilizer can enhance rice yield, but overall rice quality tends to decline with increasing yield. Therefore, to achieve high yield and superior quality of hybrid medium rice in the hot and drought-prone areas of southern Sichuan, it is essential to select suitable varieties, improve soil fertility, and focus on nutrient management during the early growth stages, with an emphasis on increasing potassium and controlling phosphorus, to synchronously enhance yield and quality.