Effects of potassium fertilizer reduction on crop grain yield and quality under rice–wheat rotation

Objectives In the rice–wheat rotation area of Chaohu basin, more than 70% of farmers apply excessive potassium fertilizer with its attendant negative impactions on the soil while optimum yield is not guaranteed. We studied the effects of reduced potassium fertilizer application on grain yield and nutrient quality of rice and wheat.

Methods Field experiments were conducted at the Comprehensive Experimental Station in Middle Anhui of Anhui Agricultural University from 2017 to 2019. The treatments in the experiment included no potassium application (CK), farmers’ practice (K₂O 90 kg/hm², K1), and 10% reduction (K₂O 81 kg/hm², K2), 20% reduction (K₂O 72 kg/hm², K3) and 30% reduction (K₂O 63 kg/hm², K4) based on the farmers’ practice. At maturity, grain yield, yield components, protein, micronutrients and their bioavailabilities in rice and wheat were determined.

Results Compared with K1, both K3 and K4 treatment did not significantly influence rice and wheat yields; K3 did not affect protein content, but increased gliadin content by 37.5% and decreased glutenin by 32.3% in rice grain (P<0.05), and had no significant effect on gliadin and glutenin content in wheat grain; K4 decreased the protein content in rice and wheat grains by 5.4% and 17.5%, but increased rice gliadin content by 43.8% while decreasing its glutenin content by 32.3%, however, it decreased wheat gliadin by 16.3%. Compared to K1, the reduced K treatments increased the Fe, Cu and Zn contents of rice and wheat grains by 3.3% and 6.7%, 34.5% and 7.8%, 18.6% and 5.7%, respectively; reduced the P/Fe, P/Cu and P/Zn molar ratios by 7.1% and 18.3%, 34.1% and 23.1%, 19.1% and 17.9%, respectively and improved bioavailability of grain Fe, Mn, Cu and Zn.

Conclusions For Chaohu basin rice-wheat rotation system, the 20% reduction of K fertilizer optimizes the protein content and components of the grains to some extent, increases the concentration of microelements and their bioavailability without reducing the grain yield of rice and wheat. Therefore, 20% reduction of K fertilizer (K₂O 72 kg/hm²) is recommended for this region and other similar conditions.