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Understanding maize (Zea mays L.) grain yield in relation to K uptake requirements is essential for devising optimized K fertilizer management practices and agricultural policies to increase grain yield for food security. A database comprising 953 measurements was created using 56 on-farm and research station experiments during 2000 to 2012 in the North China Plain (NCP) to determine K uptake requirements and patterns of K accumulation pre- and post-silking with different yield levels. The K requirement Mg-1 grain yield (Kreq.) in the K = Opt. treatment was 15.0 kg, which was lower than 20.0 kg in the K > Opt. treatment. In the Optimal K treatment, average K values were 15.0, 14.8, 14.8, and 15.7 kg for grain yields ranging from <8.0, 8 to 10, 10 to 12, and >12.0 Mg ha-1, respectively. The relative consistency of Kreq. values with increasing grain yield was mainly attributed to an offset in the increase in stover K (from 14.0 to 18.1 g kg-1), an increase in harvest index (HI) from 0.49 to 0.54, and the stability of grain K concentrations (about 3.2 g kg-1). Higher percentages for K accumulation at the post-silking stage were observed with >12 Mg ha-1 (24%) and 10 to 12 Mg ha-1 (22%) compared to <10 Mg ha-1 (9%). In conclusion, maintaining adequate K supply and post-silking K accumulation is essential for achieving high-yield maize production. [ABSTRACT FROM AUTHOR]

Investigating critical N concentration, that is, the minimum N concentration necessary to achieve maximum growth, provides insights into N nutrition and can serve as a guide to improving agricultural practices and regulations. Our objectives were to evaluate N dilution curves for deficient, optimal, and excess added N and to determine the critical N dilution curve for winter wheat (Triticum aestivum L.) in the North China Plain (NCP) based on 15 N fertilization experiments with three to six N fertilization rates. The N supplements significantly affected the N dilution curve, and increased N supply generally resulted in a greater N concentration. The critical N dilution curve for winter wheat was described by the equation nitrogen concentration (Nc) = 4.15 W-0.38 when aboveground biomass was between 1 and 10 Mg dry matter (DM) ha-1. When aboveground biomass was <1 Mg DM ha-1, the constant critical value N = 4.15% DM, which was independent of aboveground biomass. This curve was lower than that of winter wheat in France. This critical N dilution curve was validated through the nitrogen nutrition index (NNI) defined as the ratio between measured N concentration and critical Nc. The critical N dilution curve holds promise as an efficient tool for guiding N-fertilization practices and regulations for winter wheat production in the NCP. [ABSTRACT FROM AUTHOR]