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The restoration of soil organic matter (SOM, as measured by soil organic carbon (SOC)) within the world's agricultural soils is imperative to sustaining crop production and restoring other ecosystem services. We compiled long-term studies on the effect of management practices on SOC from Iowa, USA—an agricultural region with relatively high-quality soil data—to highlight constraints on detecting changes in SOC and inform research needed to improve SOC measurement and management. We found that strip-tillage and no-tillage increased SOC by 0.25–0.43 Mg C ha−1 yr−1 compared to losses of 0.24 to 0.46 Mg C ha−1 yr−1 with more intensive tillage methods. The conversion of cropland to perennial grassland increased SOC by 0.21–0.74 Mg C ha−1 yr−1. However, diversifying crop rotations with extended rotations, and supplementing synthetic fertilizer with animal manure, had highly variable and inconsistent effects on SOC. The improved prediction of changes in SOC requires: the use of methods that can identify and disentangle multiple sources of variability; looking beyond total SOC and toward systematic collection of data on more responsive and functionally relevant fractions; whole-profile SOC monitoring; monitoring SOC in long-term studies on the effect of multiple conservation practices used in combination; and deeper collaboration between field soil scientists and modelers. [ABSTRACT FROM AUTHOR]

Purpose: Paddy soils may play an essential role in global greenhouse gas mitigation and food security; however, ecological indices of soil organic carbon (C), total nitrogen (N), and total phosphorus (P), and their environmental controls in paddy soils at regional scale, are not fully understood. The aim is to quantify the stoichiometry ratio of C, N, and P, and its correlation with environmental factors in subtropical paddy soils. Materials and methods: A first-hand regional-scale field survey of subtropical paddy soil profiles was conducted in the Hunan Province of central China. The survey included 110 paddy sites and 587 soil horizons. Pearson correlation analysis was employed to investigate the correlation of soil C:N:P ratio with altitude, parent material, soil horizon, soil group, and soil physiochemical properties. Results and discussion: The depth-weighted average value of C:N, C:P, N:P, and C:N:P ratios in subtropical paddy soil profiles was 12.6, 49, 3.9, and 38:3:1, respectively. Soil organic C content was positively related with total N content, and the average C:N ratio did not vary distinctly with parent materials or soil groups. In contrast, there was no relationship neither between soil organic C and total P nor between total N and total P, and the mean values of both C:P and N:P ratios varied significantly with parent materials, soil groups, and soil horizons. Correlation analysis showed that C:N ratio was only correlated with altitude and soil bulk density, whereas C:P and N:P ratios were correlated not only with altitude and soil bulk density but also with soil texture (sand, clay, silt), and total iron and its dithionite-citrate-bicarbonate (DCB)–extractable fraction. Conclusions: Our study suggests a strong coupling effect between element C and N, but noncoupling effect between C and P and between N and P in subtropical paddy soils. The ratios of C:P and N:P are inconstant and more sensitive to environmental factors than C:N ratio. [ABSTRACT FROM AUTHOR]

Some plant species are able to acquire non-exchangeable forms of K, which improve K availability and cycling in cropping systems, and which may explain the lack of response to K. However, this would not be expected in soils dominated by kaolinite. The aim of this study was to assess non-exchangeable K (Kne) use by three selected plant species grown in a tropical Haplic Plinthosol with low exchangeable K (Ke). A greenhouse experiment was conducted with soybean (Glycine max L., Merr.), maize (Zea mays L.), and ruzigrass (Urochloa ruziziensis) with or without K fertilization for three growing cycles. The crop treatments were compared with a control without plants. In the absence of K fertilization, all the tested plants were able to use non-exchangeable K and non-exchangeable K contributed more than 80% of the K demand of the plants in the first growing cycle, even in this kaolinitic soil. In the first growing cycle, soybean and maize took up more non-exchangeable K than ruzigrass, concomitant with higher dry matter yields. Over the three crop cycles, as both biomass yield and K uptake decreased in the unfertilized systems, the dependence of plants on non-exchangeable K decreased. Unfertilized ruzigrass showed a strong ability to acquire non-exchangeable K from the soil. Over the course of three growing cycles, K application decreased the absolute uptake of non-exchangeable K as well as its fractional contribution to total K uptake by the crops. [ABSTRACT FROM AUTHOR]

Recognition that soil resources are fragile has increased interest in soil health promoting practices (SHPPs) and ways to monitor changes in agricultural soil health. To enhance this effort, inexpensive and user-friendly methods are needed. Especially methods to measure biological activity, which is central to soil health but current methods are expensive and inconvenient. Our objective was to quantify biological activity by monitoring decomposition (via mass loss) of common household items [green and rooibos tea (Camellia sinensis and Aspalathus linearis), bleached cotton (Gossypium hirsutum), and birch craft sticks (Betula spp.)], and compare these results with common laboratory measurements of biological soil health (microbial biomass carbon and nitrogen, permanganate oxidizable carbon, and potentially mineralizable carbon and nitrogen). First, we compared both strategies using correlation, including with the yield of the dominant crop in the region [maize (Zea mays L.)]. Second, we evaluated their response to several long-term SHPPs: (i) biochar, (ii) winter cover crops, (iii) nitrogen fertilizer, (iv) no-tillage, (v) diversified rotation, (vi) perennial crops, (vii) crop residue addition/removal, and (viii) prairie restoration. Correlations between decomposition and laboratory measurements were poor and often negative. Maize yield positively correlated with tea decomposition but not with the laboratory indicators. Based on 'signal-to-noise' ratios, or magnitude of SHPP treatment effect compared to variability, measurements of decomposition, especially mass loss of rooibos tea (for 4 days) and bleached cotton (for 35 days), outperformed many of the laboratory indicators in detecting treatment differences. Decomposition was also easier and less expensive than laboratory methods indicating it is a simple, yet scientifically defensible, alternative for measuring soil biological health in agroecosystems. • Laboratory soil health indicators were compared to decomposition of household items. • Decomposition of tea positively correlated with maize yield, laboratory indicators did not. • Rooibos tea decomposition had greater signal-to-noise than laboratory indicators. • Bleached cotton decomposition was variable, but showed large treatment effects. • Household item decomposition is an accessible alternative to laboratory indicators. [ABSTRACT FROM AUTHOR]