Effects of long-term potassium fertilization on potassium uptake, utilization and soil potassium balance in double maize cropping system

Objectives Potassium (K) nutrition is fundamental to maize ( Zea mays L.) productivity. The effect of long-term, large-scale exogenous K input on the K absorption and utilization of maize and the soil K balance were studied to determine the corresponding optimum yield of maize and efficiency of K fertilizer.

Methods The long-term fertilization experiment was established in 1986 on a red soil of Jinxian County of Jiangxi Province, the planting system is annually double maize cropping. Test treatments included no fertilizer control (CK), chemical N and P fertilizer (NP), chemical NPK fertilizer (NPK), double amount of chemical NPK fertilizer (DNPK), chemical NPK fertilizer with manure (NPKM) and manure alone (OM). The maize grain yield and biomass, and the K contents in plants and soil were measured at each harvest; K uptake and K use efficiency (KUE) were as well calculated.

Results The annual average grain yield and K uptake of maize in NPK, DNPK, NPKM and OM treatments were higher than NP treatment during the 33 years. There was no significant difference in grain yield and K uptake of maize among NPKM, DNPK, OM and NPK treatments during 1986‒1995. However, during 2006‒2015 and 2016‒2018, the grain yield and K uptake of maize in NPKM were increased by 129.9%‒246.7% and 55.2%‒62.1% than NPK treatment, respectively. During the 33 years of observation, OM treatment gave the highest KUE while DNPK had the least. During 2016‒2018, the KUE of NPKM treatment was 56.0% and 119.2% higher than NPK and DNPK treatments, respectively. Compared with NPK in 1996‒2005, 2006‒2015 and 2016‒2018, the K harvest index of NPKM treatment was increased by 61.6%, 53.5% and 35.8% and the K agronomic efficiency increased by 23.3%, 227.8% and 445.5% respectively. The soil K was in excess throughout the 33 years in all K fertilization treatments, except for OM and NPKM treatments during 1986‒1995, which had 53.2%‒211.6% higher residual K than NPK treatment. Every 1 kg/hm² increase of residual K resulted to a respective increase in available K content by 1.40, 1.18 and 2.60 mg/kg in 1996‒2005, 2006‒2015 and 2016‒2018.

Conclusions Under the tested K fertilization program for double maize cropping system of south China, the K budget was surplus, except for the single manure application during the first 10 years of the study. However, the amount of potassium fertilizer and the source of potassium fertilizer had no significant effect on the uptake of potassium in maize. Combining application of chemical N‒P‒K of 100‒26‒100 kg/hm² and 15000 kg/hm² of fresh pig manure in long-term are effective in keeping maize yield optimum, enhancing K uptake and K-use efficiency. K surplus increase available K content in acid soil, and with the extension of experiment years, the increasing effect of K surplus on soil available potassium increased gradually.