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Potassium (K) is an essential macronutrient for maintaining crop productivity, but the economic benefit of K fertilizer often has been neglected. We collected a database from 60 maize field experimental sites in Northeast China between 2005 and 2012 to study the impacts of potassium (K) application rates on yield, K concentrations in grain and straw, plant K uptake, and to evaluate the economic optimum K rate (EOKR) for maize under different levels of soil indigenous K supply (IKS). The results showed that the average maize yield in K rec treatment (the recommended K rate) was highest and was 32.1% higher than that in K 0 treatment (no K fertilization). Compared to K 0 , the application of K did not significantly increase grain K concentration, whereas it significantly increased K concentration in the straw. Plant K uptake in K 150 treatment (150% of the recommended K rate) was higher than that in K rec treatment, but grain yield was lower than that in K rec treatment. Thus, the result indicates that luxury K absorption occurred in K 150% treatment due to excessive K application. Thus, the application rate of K should be further optimized. Based on the modified Mitscherlich model, the average economic optimum K rate (EONR) was 135.24, 124.27, and 96.54 kg K 2 O/ha for the low, medium, and high levels of soil indigenous K supply (IKS), respectively. The average economic optimum yield (EOY) at a high IKS level was similar to the average yield in K rec treatment, whereas the EOKR could reduce by a K rate of 37.9-63.7 kg K 2 O/ha compared to K rec treatment. This study highlights the importance of K application to improve grain yield and provides a promising fertilizer recommendation method for minimizing fertilizer inputs and optimizing maize production.

The balance between fertilizer application and plant nutrient demand is essential for ensuring agricultural production because it is effective to prevent nutrient deficiency and excess, especially for soybean. This study used data from 29 sites of field experiments carried out in the soybean planting area of Liaoning province, China in 2011 to 2013. We (i) study the characteristics of yield, nutrient concentration, and harvest index to (ii) valuate the balanced nutrient uptake at different potential yield levels for soybean. The grain yield ranged from 804 to 4484 kg/ha, and average N, P, and K concentrations in grains were 45.7, 5.0, and 10.1 g/kg, respectively, while those in straw were 14.1, 1.8, and 6.7 g/kg, respectively. Average harvest index values of N, P, and K were 0.69, 0.65, and 0.52 kg/kg, respectively, while approximately 69% N and 65% P of the plant were stored in soybean grain, and 48% K was stored in straw. The two boundary lines of the QUEFTS (quantitative evaluation of the fertility of tropical soils) model were aN = 10.5, dN = 20.6, aP = 65.6, dP = 289.6, aK = 30.4, and dK = 162.7 as model parameters. The QUEFTS model estimated the balanced nutrient uptake with yield targets increased following a linear–parabolic–plateau curve. A continual linear increase in grain yield with 65.5 kg N, 7.0 kg P, and 13.9 kg K was required to produce 1000 kg grain, until the yield target reached approximately 60–70% of the potential yield, and the corresponding ratio of N, P, and K was 9.35:1:1.8. Results could be used to estimate balanced nutrient uptake to prevent excessive fertilizer being applied and reduce environment risk for ensuring sustainable agricultural development.

Potato tuber quality is influenced by the interaction of soil nutrients. Hence, simple correlation analysis cannot accurately reflect the true relationship between soil nutrients and potato tuber quality. In this study, potato tuber quality and soil nutrient content were used as research materials in the Loess Plateau of China. The partial least square regression (PLSR) method was used to establish the regression equation between potato quality and soil nutrient. The major soil nutrient indexes influencing potato quality were screened out to provide theoretical basis for potato field management. The results showed that the major soil nutrient factors influencing the potato tuber quality in Loess Plateau were soil ammonium nitrogen, soil nitrate nitrogen, soil available phosphorus, pH, and soil available potassium. Soil pH value is the most important factor affecting potato starch, reducing sugar content, and soluble protein content. Soil nitrate nitrogen is one of the important factors affecting potato tuber soluble total sugar content, vitamin C, browning intensity, and polyphenol oxidase activity. Soil ammonium nitrogen was positively correlated with the total soluble sugar content of potato tubers, and negatively correlated with reducing sugar content, browning intensity, and polyphenol oxidase activity. However, soil available potassium has positive effects on potato starch and reducing sugar content, and negative effects on soluble protein and browning strength. Results of this study indicates that the major soil nutrient factors influencing potato tuber quality were soil nitrate nitrogen and soil pH value.

Optimizing the phosphorus (P) application rate can increase grain yield while reducing both cost and environmental impact. However, optimal P rates vary substantially when different targets such as maximum yield or maximum economic benefit are considered. The present study used field experiment conducted at 36 experiments sites for maize to determine the impact of P application levels on grain yield, plant P uptake, and P agronomy efficiency (AEP), P-derived yield benefits and private profitability, and to evaluated the agronomically (AOPR), privately (POPR), and economically (EOPR) optimal P rate at a regional scale. Four treatments were compared: No P fertilizer (P0); P rate of 45–60 kg ha−1 (LP); P rate of 90–120 kg ha−1 (MP); P rate of 135–180 kg ha−1 (HP). P application more effectively increased grain yield, reaching a peak at MP treatment. The plant P uptake in HP treatment was 37.4% higher than that in P0. The relationship between P uptake by plants (y) and P application rate (x) can be described by the equation y = −0.0003x2 + 0.1266x + 31.1 (R2 = 0.309, p < 0.01). Furthermore, grain yield (y) and plant P uptake (x) across all treatments also showed a significant polynomial function (R2 = 0.787–0.846). The MP treatment led to highest improvements in P agronomic efficiency (AEP), P-derived yield benefits (BY) and private profitability (BP) compared with those in other treatments. In addition, the average agronomically (AOPR), privately (POPR), and economically optimal P rate (EOPR) in 36 experimental sites were suggested as 127.9 kg ha−1, 110.8 kg ha−1, and 114.4 kg ha−1, which ranged from 80.6 to 211.3 kg ha−1, 78.2 to 181.8 kg ha−1, and 82.6 to 151.6 kg ha−1, respectively. Economically optimal P application (EOPR) can be recommended, because EOPR significantly reduced P application compared with AOPR, and average economically optimal yield was slightly higher compared with the average yield in the MP treatment. This study was conducive in providing a more productive, use-effective, profitable, environment-friendly P fertilizer management strategy for supporting maximized production potential and environment sustainable development.

Enhancing agricultural productivity with the minimum possible cost to the environment is crucial for sustainable agriculture development. The effective management of K fertilizer would reduce the pollution risk of fertilizer residue. The data from the 29 experimental sites for rice in Liaoning province were used to determine the effect of different K fertilizer management in increasing yield, K uptake, and potassium fertilizer contribution rates (FCRK) for rice. The relationship among rice yield, biomass accumulation and plant K uptake, and recommended reasonable K fertilizer application rates in different inherent soil productivity levels were evaluated. The four treatments comprised no K fertilizer (K0), K fertilizer application of 60kg ha-1 (K60), 120kg ha-1 (K120), and 180kg ha-1 (K180). The K120 treatment showed a significant yield increase (16.59%) compared to the K0 treatment in this study. The average K uptake of grain in the K60, K120 and K180 treatments was 23.1, 24.8 and 24.9 kg ha-1, which was significantly higher by 12.67%, 20.77%, and 21.48% compared to the K0 treatment. The average K uptake of grain, straw and plant was highest in K180 (134.8 kg ha-1), followed by the K120 and K60. Additionally, the correlation between grain yield, biomass accumulation (y) and plant K uptake (x) showed a significant positive polynomial function. The equation was y = −0.406x2 + 110.43x + 639.3 and y = −0.237x2 + 135.3x + 3796.2, respectively. The FCRK followed the sequence as K180 < K60 < K120. Furthermore, the recommended K application rates in the 29 experimental sites were ranged from 92.8 to 134.5 kg ha-1, and the corresponding theoretical yield of recommended K rate were ranged from 7371.5 to 11144.5, and with an average of 9297.5 kg ha-1. Remarkably, the average recommended K rate in the four inherent soil productivity levels was 116.1, 111.2, 112.2 and 111.7 kg ha-1 and the corresponding average theoretical yield was 9966.1 kg ha-1, 10158.8 kg ha-1, 8373.2 kg ha-1 and 8881.9 kg ha-1. The results of this study suggest that different inherent soil productivity levels have different K application rates and yield performance. This result somewhat strengthens the finding of this study that moderate K application is conducive to effectively improving the yield and to the enhancement of agricultural productivity, which is conducive to the sustainable environment.

Changes in soil carbon (C):nitrogen (N):phosphorus (P) stoichiometry have great significance on understand regulatory mechanism and restoration of ecosystem functions. However, the responses of C, N and P stoichiometry to soil depth and different vegetation types remains elusive. To address this problem, the study aims to explore the effects of soil depth and vegetation types on soil C, N, and P stoichiometry, and their relationships with microbial biomass in low mountain and hill region of China. The results indicated that soil SOC and TN concentrations in oak forest were markedly higher than those in grassland, and the vertical distribution of SOC and TN concentration showed an inverted triangle trend as the soil deepens. However, there was no significant change in soil TP concentration among 0–20 cm, 20–40 cm, and 40–60 cm. Soil C/N among different layers (0–20, 20–40, and 40–60 cm) is narrower fluctuation margin, and its value is basically stable within a certain range (11–14.5). Both soil C/P and N/P showed significant variability in different vegetation types, and soil N/P decreased with soil layers deepen. Both the microbial biomass C (MBC) and N (MBN) showed a decreasing trend with the increase of soil depth, and three soil layers from high to low was: oak forest > pine forest > grassland. Our results will potentially provide useful information for the vegetation restoration and forest management and great significance to enrich the scientific theory of ecological stoichiometry.

Accurate estimating of the balanced nutrition for maize is necessary for optimizing fertilizer management to prevent nutrient supply surplus or deficiency. Data from 300 field experiments in the Northeast China conducted between 2006 and 2011 were gathered to study the characteristics of maize yield, and using the QUEFTS model to estimate the balanced nutrition at different yield potential. The average grain yield was 10 427 kg/ha, and average internal efficiencies were 54.3, 251.5 and 78.2 kg grain per kg plant nitrogen (N), phosphorus (P) and potassium (K), respectively. With the harvest index values &lt; 0.40 as outliers were excluded, the model simulated a linear-parabolic-plateau curve for the balanced N, P and K uptake when the initial yield target increased to the yield potential levels of 10 000 to 14 000 kg/ha. When the yield target reached approximately 60–70% of the yield potential, 16.7 kg N, 3.8 kg P, and 11.4 kg K were required to produce 1000 kg grain. The corresponding internal efficiencies were 60.0, 265.7 and 88.0 kg grain per kg plant N, P and K, respectively. These results contributed to improving nutrient use efficiency, and to demonstrate that the QUEFTS model could be a promising approach for estimating the balanced nutrition.