Managing Agricultural Nutrients for Food Security in China: Past, Present, and Future
Over the past 2000 yr, agriculture in China has transformed from a low-input, low-output organic-based system to an intensive production system that relies heavily on inorganic inputs. The modern high-input, high-output system has provided the nation with basic food self-sufficiency, although at escalating environmental costs. Meanwhile, crop production has been nearly stagnant since the mid-1990s, despite continued increases in production inputs, such as chemical fertilizers. In the future, China must increase agricultural output by 50% to meet its growing food demand. New advances to increase agricultural productivity and improve resource (e.g. N and P) use efficiency will be critical in China for sustainable agriculture and ecosystem services. Here, we discuss an integrated soil-crop system management (ISSM) paradigm that may help achieve the sustainable intensification goal. This paradigm features (i) improving soil quality, (ii) enhancing the use of various nutrient resources, (iii) closing the yield gap, and (iv) effectively reducing N losses. Recent on-farm trials based on ISSM principles almost doubled corn yield, while fertilizer N amounts were similar to current farming methods. This ISSM in China is a novel agricultural paradigm that can improve food security and environmental quality worldwide, especially in regions of high input with low-efficiency systems.
Application of Kinetic Models in Describing Soil Potassium Release Characteristics and their Correlations with Potassium Extracted by Chemical Methods
Potassium (K) release characteristics in soil play a significant role in supplying available K. Information on K-release characteristics in soils of central Iran is limited. The objectives of this study were to determine K release characteristics and correlations of K release rate constants with K extracted by different chemical methods in surface soils of ten calcareous soils of central Iran. The kinetics of K release in the soils was determined by successive extraction with 0.01 mol L-1 CaCl2 in a period of 2--2 017 h at 25±1 oC. Soil K was extracted by distilled water, 0.5 mol L-1 MgNO3, 0.002 mol L-1 SrCl2, 0.1 mol L-1 BaCl2, 0.01 mol L-1 CaCl2, 1 mol L-1 NaCl, 1 mol L-1 boiling HNO3, 1 mol L-1 NH4OAC, Mehlich 1, 0.002 mol L-1 SrCl2 0.05 mol L-1 citric acid, and ammonium bicarbonate-diethylenetriamine pentaacetic acid (AB-DTPA). A plot of cumulative amounts of K released showed a discontinuity in slope at 168 h. Thus, two equations were applied to two segments of the total reaction time (2--168 and 168--2017 h). Cumulative amounts of K released ranged from 55 to 299 mg kg-1 in 2--168 h and from 44 to 119 mg kg-1 in 168--2 017 h. Release kinetics of K in the two time segments conformed fairly well to parabolic diffusion, simplified Elovich, and power function models. There was a wide variation in the K release rate constants. Increasingly higher average concentrations of soil K were extracted by distilled water, Mehlich 1, SrCl2, CaCl2, SrCl2 + citric acid, AB-DTPA, MgNO3, NaCl, NH4OAc, BaCl2 and HNO3. Potassium release rate constants were significantly correlated with K extracted. The results of this study showed that information obtained from mathematical modeling in two reaction time segments can help to estimate the K-supplying power of soils.
