Effects of potassium fertilizer and potassium use efficiency on early-, mid- and late-season rice in Hubei province, China

Multipoint field experiments with early-, mid- and late-season rice cultivars were conducted in 18 counties of Hubei province during 20062009. The objective of the research was to study the effect of potassium fertilizer on rice yield and yield component factors, and to investigate potassium (K) uptake and K use efficiency under present production conditions. The average yields of early-, mid- and late-season cultivars of NPK (with K) treatment were 6589, 8329 and 6789 kg/ha, respectively, which were 716, 679 and 691 kg/ha higher than those of NP (without K) treatment. The yield increase rate of early-, mid- and late-season cultivars was 12.6%, 9.6% and 12.0%, respectively, corresponding to 10.8%, 8.2% and 10.3% of the K contribution rate, respectively. It was concluded that the application of K significantly increased grain yield, which resulted from an increased number of panicles per unit area in early-season rice, increased numbers of panicles per unit area and grains per panicle in mid-season rice, and increased number of grains per panicle and seed-setting rate in late-season rice. Application of K also increased total K2O accumulation and K2O absorption of 100-kg seeds, and decreased K2O harvest index. Under present production conditions, K2O absorption of 100-kg seeds of early-, mid- and late-season cultivars was 2.96, 3.45 and 2.72 kg, respectively. K use efficiency of early-, mid- and late-season rice were respectively as follows: K2O agronomic efficiency of 9.6, 8.2 and 7.2 kg/kg, partial factor productivity of applied K2O of 92.3, 101.5 and 75.4 kg/kg, K2O recovery efficiency of 47.1%, 53.8% and 46.3%, and K2O physiological efficiency of 21.1, 24.1 and 23.7 kg/kg. The soil K dependent rate of early-, mid- and late-season rice was 78.0%, 83.0% and 70.4%, respectively. As a whole, the K uptake and K use efficiency of early-, mid- and late-season rice differed, but K absorbed by the three kinds of rice primarily came from the soil and not from K fertilizer. As a result, sustaining and increasing soil K fertility is an effective measure to increase rice yield and conserve chemical K fertilizer resources.