Potassium (K) input is essential for the improvement of soil fertility in agricultural systems. However, organic amendment may differ from mineral K fertilization with respect to modifying the soil K transformation among different fractions, affecting soil K availability. We conducted a 60-day lab incubation experiment to evaluate the response of soil K dynamics and availability in various fractions with a view to simulating crop residue return and chemical K fertilization in an Anthrosol of northwest China. The tested soil was divided into two main groups, no K fertilization (K0) and K fertilization (K1), each of which was subjected to four straw addition regimes: no straw addition (Control), wheat straw addition (WS), maize straw addition (MS), and both wheat straw and maize straw addition (WS+MS). Soil K levels in the available (AK) and non-exchangeable (NEK) fractions were both significantly increased after K addition, following the order of K>WS>MS. Fertilizer K was the most efficient K source, demonstrating a 72.9% efficiency in increasing soil AK, while wheat and maize straw exhibited efficiencies of 47.1% and 39.3%, respectively. Furthermore, K fertilization and wheat and maize straw addition increased the soil AK in a cumulative manner when used in combination. The mobility factor (M F) and reduced partition index (I R) of soil K were used to quantitate the comprehensive soil K mobility and stability, respectively. Positive relationships were observed between the M F and all relatively available fractions of soil K, whereas the I R value of soil K correlated negatively with both M F and all available fractions of soil K. In conclusion, straw amendment could be inferior to mineral K fertilization in improving soil K availability when they were almost equal in the net K input. Crop straw return coupled with K fertilization can be a promising strategy for improving both soil K availability and cycling in soil-plant systems.
Combined foliar application of zinc sulphate (ZnSO4) and selenium (Se) has been practiced in wheat biofortification. However, it remains elusive that whether the combined application affects Zn and Se distribution to grain, the efficacy of biofortification and bioavailability in wheat, due to the accompanying sulphate sources. Selenite and ZnSO4 were applied either alone or simultaneously to foliage of wheat in field, and their impacts on Zn and Se partitioning in plants, enrichment and bioavailability in whole grain, bran and flour, as well as amino acid profile in flour, were closely investigated. Grain yield was not influenced by any of the foliar Zn and Se applications. Grain Zn and Se concentrations reached 58.3–77.9 and 0.30–0.74 mg kg−1 in Zn‐ and Se‐sprayed plants, respectively, and the estimated daily‐absorbed Zn by a reference adult from grain and flour were enhanced by 1.2‐ to 2.4‐fold than the control, as well as 16.8‐fold increase on average for daily Se intake. Combined Zn and Se application led to a 32%–37% reduction in Se concentrations and daily Se intake of whole grain and flour in one of the two seasons when compared with the foliar Se spray alone, which was partly associated with the reduced Se distribution to grains. Alternatively, similar responsive patterns of methionine and cysteine with grain and flour Se concentrations further suggested that zinc sulphate and selenium interactions in Se accumulation act through the metabolism of sulphur‐containing amino acids in wheat plants. Further, the substantial Zn enrichment in flour paralleled to the increase of amino acid profiles such as aspartate, glutamate, glycine and lysine, but not to the total amino acid content. Overall, wheat was successfully biofortified with Zn and Se through combined foliar applications, although an antagonistic impact of ZnSO4 spray on the magnitude of Se biofortification occurred in some cases.
Straw mulching can be affected by N fertilization rate with regard to improving soil organic carbon (SOC) lability, which modifies the net accumulation of SOC and soil aggregation. We conducted a 14-yr field experiment to determine how straw mulching coupled with N application rates affects crop yield, SOC sequestration as a net gain of SOC, and soil aggregation in a winter wheat (Triticum aestivum L.) monoculture system. Six combinations of two cultivation practices, conventional cultivation (CC) and straw mulching (SM), and three N application rates (0, 120, and 240 kg N ha -1 ) were compared. Results revealed that SM did not affect wheat yield throughout the 14 yr of cultivation, but increased the SOC stock, SOC lability, and the carbon management index (CMI) in surface soil (0-20 cm). Instead, N application, N120 and N240, increased the wheat production almost equally, and followed a trend for increasing SOC stock: N240 > N120 > N0; however, a different trend for increasing SOC lability and soil CMI (N120 > N240 > N0). Soil macro-aggregation was increased by SM but decreased with increasing N application. Principal component analysis (PCA) indicated that organic C input was the key to improving SOC sequestration, SOC lability, and soil macro-aggregation rather than N input, especially high N input (N240) reduced SOC lability and soil aggregation in soil. Consequently, medium N application (N120) may be expected to couple with straw directreturning for improving soil productivity and quality in this agro-system.
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