Long-term effect of fertilizer application on rice yield, potassium uptake in plants, and potassium balance in double rice cropping system

Abstract

A 27 years field experiment was conducted on a Fe-Accumli Stagnic Anthrosol to evaluate the effects of long-term application of fertilizer, pig manure (PM), and rice straw (RS) on rice yield, uptake, and usage efficiency of potassium, soil K pools, and the nonexchangeable K release under the double rice cropping system in South Central China. Common cropping pattern in the study was early rice-late rice-fallow (winter). The field treatments included CK (no fertilizer applied), NP, NK, NPK, and NK + PM, NP + RS, NPK + RS. The pig manure and rice straw was applied in both the early rice and late rice cropping season. The ranking order of 27 years average annual grain yield were the CK<NK<NP<NK + PM<NP + RS<NPK<NPK + RS treatments. The negative yield change trends were observed in the CK and NP and NK treatments of unbalanced nutrient application in the case of omitted-K and P-omitted. The positive yield change trends were observed in balanced applications of NPK and combined application of fertilizer (NPK) with pig manure (NK + PM) or rice straw (NP + RS and NPK + RS). The application of K fertilizer (NPK) increased grain yield by 56.7 kg·hm−2·a−1 over that obtained with no K application (NP). The combined application of pig manure with fertilizer (NK + PM) increased by 82.2 kg·hm−2 per year compared with fertilizer application alone (NK). The combined application of rice straw with fertilizer (NP + RS and NPK + RS) increased on the average of 34.4 kg·hm−2 per year compared with fertilizer application alone (NP and NPK). In all fertilizer, pig manure and rice straw combinations, K uptake change trends in rice plants of the early rice was positive except for CK and NP treatments. The results showed that the total removal of K by the rice plants exceeded the amounts of total K applied to the soil in all treatments, which showed a negative K balance. This ranged from 106.3 kg·hm−2·a−1 in CK treatment to 289.6 kg·hm−2·a−1 in the NPK + RS treatment. Continuous annual application of 199.2 K kg·hm−2 to rice resulted in an accumulation (58 kg·hm−2) of exchangeable K (1 mol NH4OAc extractable K) in 0–45 cm soil depth over the study period, despite the higher average annual uptake of K by the system (225.7 kg·hm−2). However, nonexchangeable K increased substantially from 1090 kg·hm−2 to 1113 kg·hm−2 and 1140 kg·hm−2 in the 0–45 cm soil layer in NPK + RS and NPK treatments after 27 years of the continuous double rice cropping system, respectively. Thus, long-term rational application of K fertilizer may increase sustainable K fertility of the continuous double rice cropped system.