Effects of lateral deep application and dosage of slow-release fertilizer on yield and fertilizer utilization efficiency of rape (Brassica napus L.)

In order to determine the effects of lateral deep application of slow-release fertilizer for direct seeding rapeseed in red soil paddy field, 2 a(2018－2020) field experiments covering two winter rapeseed(late-maturity varieties“Dadi 199” and early-maturity varieties“Zhongyou 607”) were conducted with 3 treatments, including no fertilization(F0), broadcast fertilization on soil surface (F1) and lateral deep application fertilizer(F2). The slow-release fertilizer (N 25%, P2O5 7% and K2O 8%) was used with application rate of 750 kg/hm2 for late-maturity rapeseed and 600 kg/hm2 for early-maturity rapeseed, respectively. At the same time, conventional fertilization experiments were carried out on two rapeseed varieties from 2019 to 2020, and the application levels of slow-release fertilizer were 0, 300, 450, 600, 750 and 900 kg/hm2, respectively. Each treatment was repeated 3 times and arranged in random blocks with a plot area of 10 m × 4 m. During the experiments, the air temperature and precipitation were measured. The harveting density, dry matter, seed yield and yield components were mearued. The absorption, agronomic efficiency, partial factor productivity and contribution rate of N, P and K were calculated. The results showed that the yield and fertilizer use efficiency of rapeseed in red-soil paddyfield were significantly affected by fertilizing methods. Moreover, the differences were more significant (P<0.05) for late-maturity varieties and rainy season(2018-2019) than for early-maturity varieties and drought season (2019－2020). Compared with F1, F2 treatment promoted the yield formation and increased the fertilizer use efficiency significantly (P<0.05). Specifically, the technique of synchronous drilling sowing with side deep fertilizing could improve dry matter production during the whole growth period of rapeseed, especially from anthesis to maturity, and with a corresponding rise of dry matter accumulation of both underground and aboveground after anthesis. At the same time, compared to the conventional cultivation, the technique of synchronous drilling sowing with side deep fertilizing increased the absorption of nutrients(N, P and K), effective harvesting density and maintained sufficient pod numbers, and thus improved the yield and fertilizer use efficiency of rapeseed. The optimal quantity of slow-release fertilizer for late-maturity rapeseed and early-maturity rapeseed were 715.39 and 586.39 kg/hm2 to target yield of 2 438.94 and 1 708.22 kg/hm2, respectively. The study indicated that lateral deep application of appropriate slow-release fertilizer has the potential of improving rapeseed productivity in red-soil paddyfield of southern China and should be suggested to applicate according to the local conditions.