Effect of potassium rates on rice yields and potassium application efficiency in double-rice cropping system under a 5-year located experiment

Effects of potassium fertilizer application on rice yield, K content in plant, K uptake, K\|fertilizer use efficiency, potassium balance and economic benefit were studied by using a five\|year (2008-2012) located experiment in double\|rice cropping system. There were five treatments, K0 (non potassium fertilizer), K1 (K2O 84 kg/ha in early rice and K2O 105 kg/ha in late rice), K2 (K2O 120 kg/ha in early rice and K2O 150 kg/ha in late rice), K3 (K2O 156 kg/ha in early rice and K2O 195 kg/ha in late rice) and K4 (K2O 192 kg/hm2 in early rice and K2O 240 kg/ha in late rice). The results show that the K fertilizer application could obviously increase grain yields of early rice and late rice, and under a certain K fertilizer application range, the yield is increased with the increase of potassium application rate. The potassium uptook by rice plant, especially by rice straw is obviously increased with the increase of K fertilizer application amount. The K agronomy efficiency of the K2 treatment is the highest in both early rice (3.12 kg/kg K2O) and late rice (3.70 kg/kg K2O) among all the treatments, and the K recovery efficiency of K1 treatment is the highest in both early rice (41.2%) and late rice (76.4%) and the K recovery efficiency is decreased with the increase of K application amount. K fertilizer application could significantly affect K contents in soils, and the contents of available K, slowly available K and total K in soils are increased with the increase of K fertilizer application amount and the differences of available K among treatments are significant (P＜0.01). The apparent K balance in the soil\|crop system is negative in the K0, K1 and K2 treatments (127.1 kg/ha, 58.3 kg/ha and 10.8 kg/ha) after the five\|year rice\|cropping and the potassium deficient amount is decreased with the increase of K fertilizer application amount, while the apparent K balance is positive in the K3 and K4 treatments (48.0 kg/ha and 109.2 kg/a) and potassium surplus amount is increased with the increase of K fertilizer application amount. The ratios of output to input of K fertilizer of the K2 treatment in both of early rice (1.04) and late rice (1.27) are the highest. The overall results suggest that the appropriate potassium application rates are K2O 120-156 kg/ha in early rice and K2O 150-195 kg/ha in late rice in this double\|rice cropping area.