Optimum amount of potassium fertilizer based on high yield and soil potassium balance under straw return in rice production region of northeast China

Objectives The effects of different amounts of potassium (K) fertilizer on rice yield, K utilization efficiency and the capacity of soil K supply under straw return in rice production region of northeast China were systematically studied, in order to provide scientific basis for rational K fertilizer application under straw return of rice.

Methods A located field experiment was conducted in Qianguo County of Jilin Province during 2015–2019. Six rates of K fertilizer (K₂O) treatments were setup, including 0 kg/hm² (K0), 30 kg/hm² (K30), 60 kg/hm² (K60), 90 kg/hm² (K90), 120 kg/hm² (K120) and 150 kg/hm² (K150). After harvest each year, the grain and biomass yield, K content in plant were measured, and the contents of soil readily available, slowly available and total K in 0–20 cm and 20–40 cm depth were analyzed. The K accumulation, K utilization efficiency and apparent K balance in soil were calculated.

Results Compared with K0 treatment, the grain and biomass yields were averagely increased by 7.6%–14.5% and 6.3%–10.9%, with the highest yields in K60 and K90 treatments. The harvest indexes were not significantly different among the K treatments. K recovery efficiency, agronomic efficiency and partial productivity declined with increasing of K application rate. The treatments of K60, K90, K120 and K150 increased the contents of readily available K and slowly available K in 0–40 cm soil, but did not in the total K contents, compared with K0 and K30 treatment. There was no significant difference in readily available K and slowly available K in 0–40 cm soil among the treatments of K90, K120 and K150. The apparent K balance of soil were in deficiency under K0 and K30 treatments during the five-years period, just in balance under the K60 treatment, and surplus under the K90, K120 and K150 treatments. When surplus rate of K was 0, the simulated K application rate was 53.1 kg/hm², the achieved grain yield would be 10035 kg/hm², readily available K contents in 0–20 cm and 20–40 cm soil be 103.04 mg/kg and 91.56 mg/kg, and the K recovery efficiency, agronomic efficiency and partial productivity be 40.4%, 21.2 kg/kg and 202.2 kg/kg, by simulating between K fertilizer rate, grain yield, soil readily available K content, K utilization efficiency and surplus rate, respectively.

Conclusions Under the tested condition, the soil K apparent balance will be in deficit when annually K₂O rates is less than 30 kg/hm², just in balance when K₂O 60 kg/hm² is applied, and in surplus when K₂O rate is higher than 90 kg/hm². The high rice yield will be achieved at K₂O rate of 60–90 kg/hm², and the soil readily available and slowly available K contents will not be further increased at K₂O rate higher than 90 kg/hm². The simulated application rate with annual soil K surplus of zero is at the range of K₂O 50–56 kg/hm², in which the rice yield, the K fertilizer utilization efficiency and the capacity of soil K supply will be the highest under this experimental condition.