Effects of controlled release fertilizer ratio on yield formation and nitrogen absorption and utilization of late-maturing medium <italic>japonica</italic> rice under different mechanized cultivation methods

Abstract

<p id="C3">Rice cultivars of Nanjing 9108 with good taste quality was adopted as material under the pure nitrogen condition of 270 kg hm^-2in this study. Rice was cultivated with two methods including mechanical transplanting with pothole seedlings (MT) and mechanical transplanting with carpet seedlings (MC). Controlled-release fertilizer and quick-acting nitrogen fertilizer were mixed at a ratio of 5:5. Controlled-release fertilizer was mixed from four different release periods (40, 80, 100, and 120 days) at a ratio of 1:4 to form three mixing modes (40+80, 40+100, and 40+120). Conventional urea split fertilization (CK) was used as a control, and the effects of different controlled-release fertilizer ratios on yield formation and nitrogen accumulation of high-quality <italic>japonica</italic> rice were studied. Under the same fertilizer treatment, compared with mechanical transplanting with carpet seedlings (MC), the two-year yield of mechanical transplanting with pothole seedlings (MT) was significantly increased by 3.9% and 4.9%, respectively. The reason was that the transplanting of pothole seedling machine could improve the accumulation of photosynthetic substances in the middle and late stages and obtain larger panicle type with higher grain number per panicle, seed setting rate, and 1000-grain weight. Under the cultivation mode of pothole seedling transplanting and carpet seedling transplanting, compared with CK, the two-year yield of 40+80 and 40+100 controlled-release fertilizer treatments were higher than CK, and the two-year yield of 40+100 controlled-release fertilizer treatments was the highest, which was significantly increased by 7.3% and 9.2%, respectively. The reason was that 40+100 controlled-release fertilizer treatment had higher effective panicle number and population glume amount. Compared with 40+80 and 40+120 controlled-release fertilizer treatments, the nutrient absorption law of 40+100 controlled-release fertilizer treatment was more consistent with Nanjing 9108, which not only ensured the occurrence of early tillering, but also ensured the stable production of photosynthetic substances at later stage, thus obtaining stable panicle number, grains per panicle, and 1000-grain weight. Compared with CK, the nitrogen recovery efficiency, nitrogen agronomic efficiency, nitrogen physiological efficiency, and nitrogen partial productivity of 40+100 controlled-release fertilizer treatments were significantly increased by 10.0%-12.5%, 24.6%-30.5%, 11.4%-18.6%, and 7.3%-9.1%, respectively. In conclusion, the mechanical transplanting with pothole seedlings (MT) had obvious advantages over mechanical transplanting with carpet seedlings (MC), which was a cultivation method that was conducive to high-quality <italic>japonica</italic> rice. At the same time, the 40+100 controlled-release fertilizer ratio could better meet the nutrient requirements of good-quality <italic>japonica</italic> rice at various stages, and could obtain high yield, which could be used as a simplified fertilization scheme for high-quality <italic>japonica</italic> rice.