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Integrating foliar zinc (Zn) application into common practices, e.g. application of pesticides, phosphorus (P) or biostimulants, is a feasible agronomic strategy of wheat biofortification. However, it remains unclear how this integrated approach affects the efficacy of foliar Zn sprays, especially under unfavourable environmental conditions. Here, two field experiments considering Zn forms (ZnSO4 and zinc-glycine) and applications (alone or combined with pesticides, KH2PO4, and biostimulants amino acids or fulvic acids) were conducted in two seasons (2017 and 2018), and their effects on the magnitude of grain Zn increment and bioavailability were evaluated. The results showed that less precipitation in 2018 caused 11.7–52.2% yield losses than in 2017, which increased grain Zn concentration by 13.4–58.4%. Foliar application of Zn-glycine did not surpass ZnSO4 spray in regarding to grain Zn concentration and bioavailability. Grain Zn concentration substantially decreased in plants sprayed with KH2PO4 irrespective of Zn forms applied, indicating strong antagonistic effects of P supply on grain Zn enrichment. There were no differences in grain Zn density between the applications of amino acids and fulvic acids. However, grain Zn bioavailability significantly increased by 22.3 and 23.4% in the Zn plus pesticides treatment when sprayed with fulvic acids in 2017 and with amino acids in 2018, respectively. Overall, environmental conditions and foliar Zn management considering Zn forms and applications accounted for 35–45% and 20–37% of explained variation in the magnitude of grain Zn increment, respectively. The results demonstrated that management and environment are crucial factors to consider in agronomic biofortification of wheat.

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.

Increasing soil organic carbon (SOC) is a widely accepted strategy to offset greenhouse gases and improve soil quality. Straw return can modify SOC dynamics and increase its stock, which are also i...

We quantified the effects of different straw return modes on soil organic carbon (SOC), total nitrogen content (TN) and C:N ratios in a wheat/maize double‐cropping agricultural system by analysing their content in different soil aggregate sizes and density fractions under four modes of straw return: (a) no return/retention of wheat and maize straw (Control); (b) retention of long wheat stubble only (Wheat Stubble); (c) retention of long wheat stubble and return of chopped maize straw (Mixed); and (d) return of chopped wheat and maize straw (Both Chopped). The Mixed and Both Chopped straw return modes produced the highest crop yields. Relative to the Control, SOC stock was 9.6% greater with the Mixed treatment and 14.5% greater with the Both Chopped treatment, whereas the Wheat Stubble treatment had no effect on SOC. Mixed and Both Chopped significantly enhanced TN stock relative to the Wheat Stubble and Control treatments. Compared with the Control, the Mixed and Both Chopped treatments increased the mass proportions of large macroaggregates and reduced the silt plus clay fraction; Mixed and Both Chopped caused a significant increase in SOC and TN in large and small macroaggregates; the Mixed treatment significantly increased SOC content in the coarse and fine intra‐aggregate particulate organic matter (iPOM) density fractions of large macroaggregates, whereas Both Chopped increased SOC in the coarse iPOM, fine iPOM and mineral‐associated organic matter (mSOM) density fractions of both large and small macroaggregates; and Mixed and Both Chopped enhanced TN content in coarse iPOM and fine iPOM within small macroaggregates. Although the Mixed treatment was slightly less effective at improving C sequestration in agricultural fields than the Both Chopped treatment, the Mixed treatment may nonetheless be the optimal plant residue management mode in terms of minimizing time and labour due to its ability to improve soil structure, maintain organic carbon levels and provide a means of sustainable crop production in intensive wheat/maize double‐cropping systems.

Crop residue is a commonly used organic soil amendment in summer maize (June–October)–winter wheat (October–June of next year) rotation systems. However, the effects of different straw return modes on soil aggregation and soil organic carbon (SOC) stocks in different water-stable aggregates have not been extensively investigated in these cropping systems. The objective of this study was to quantify the long-term (7 yr) impact of C input on the SOC content of four soil aggregate size classes (large macroaggregates; small macroaggregates; microaggregates, silt plus clay fraction) and in explicit SOC fractions (free light fraction, free LF; intra-aggregate particulate organic matter, iPOM; mineral-associated matter, mSOM) within the top 40 cm of soil in a wheat–maize double cropping system in Northwest China. Four treatments were examined: (i) no return (control); (ii) return of wheat straw only (WR); (iii) return of maize straw only (MR); and (iV) return of both maize and wheat straw (MR-WR). Over the experimental period, the change in SOC under the four treatments ranged from −0.96 to 5.83 Mg ha −1 and a significant linear relationship between SOC change and cumulative C input (R 2 = 0.9882, P fine iPOM > coarse iPOM > free LF. Straw return significantly increased the C stock in iPOM and mSOM relative to the control. Coarse iPOM was the most sensitive indicator of C change and mSOM was the main form of SOC under long-term straw return. A significant linear relationship existed between cumulative C input and the mass proportion of macroaggregates as well as the C content of SOC fractions (or aggregate fractions). Soil depth had a significant influence on almost all measurements, with greater values observed in the 0–20 cm layer than in the 20–40 cm layer. Overall, return of both maize and wheat straw was the best strategy for improving soil structure, soil organic carbon, and crop yield. However, straw return from one crop was sufficient to maintain initial SOC levels, and conserved straw could be used for cellulosic feedstocks.

Organic amendments are widely used to both manage soil organic C (SOC) and improve soil fertility in agro-ecosystems. However, crop production and the mechanisms of SOC sequestration following organic amendment may be affected by long-term differential N fertilizations, hence driving the dynamics in SOC fractions in cultivated fields. Our 3-yr (2016–2019) field experiment evaluated the responses of SOC sequestration and SOC fractions to organic amendments in soils with long-term contrasting N applications in a winter wheat monoculture system. We compared wheat straw return (St) and farmyard manure application (Fm) in soils with either long-term (2002–2019) N absence (-N) or normal N application (+N). Both St and Fm increased SOC stocks in the 0–20-cm layer, but Fm increased it more than St did. However, St exhibited a greater SOC sequestration rate in +N soils than that in –N soils, whereas Fm exhibited both a lower SOC sequestration rate and efficiency in +N soils than in –N soils. SOC increased across all fractions in all soils after both St and Fm. However, compared with –N soils, +N soils exhibited a lower SOC increase, specifically in the very labile fraction after St, but in the non-labile fraction after Fm. St, Fm, and +N all increased the soil C management index (CMI), but only +N increased wheat yield and its sustainable yield index (SYI). Those relationships indicated that both straw and manure amendments were responsible for both SOC sequestration and increasing the CMI, and N input was fundamentally responsible for an increased SYI and associated plant-C input. Consequently, straw return was expected to be more effective at sequestering SOC when applied to soil having had adequate long-term N application, whereas farmyard manure application was likely more effective when applied in N-deficient soil. Our field study findings provide empirical evidence that soil N availability affects SOC sequestration capacities following organic amendments, and that impacts strategies aimed at further increasing soil fertility improvements via organic amendment, especially considering that different agro-ecosystems are subject to different fertilization regimes.

Straw return is a widely recognized strategy for increasing soil organic carbon (SOC) sequestration and improving soil quality and crop productivity. A 4-year-long field experiment established in 2008 was conducted to investigate the effects of the combined return of maize and wheat straw on the SOC stock at a soil depth of 0–20 cm in an intensive summer maize (Zea mays L.)–winter wheat (Triticum aestivum L.) cropping system in the Guanzhong Plain. The study involved four treatments with four replicates: low return of maize and wheat straw (ML–WL), low return of maize straw and high return of wheat straw (ML–WH), high return of maize straw and low return of wheat straw (MH–WL), and high return of maize and wheat straw (MH–WH). Compared with the SOC stock in the pre-experimental soil, the SOC stock in the 0–20 cm soil layer decreased by 2.6% under the ML–WL treatment, and in contrast, increased by 1.9% in ML–WH and 14.4% in MH–WH. Similarly, the stabilization rate gradually increased from 2.4% in ML–WH to 10.0% in MH–WH, though an obvious decrease of 6.8% was found in the ML–WL treatment. A significant linear relationship (P

Incorporating foliar zinc (Zn) spray into existing pesticide application is considered highly cost-effective to biofortify wheat (Triticum aestivum) with Zn. However, the effectiveness of this combined approach in terms of Zn enrichment and bioavailability in grain and its milling fractions is not well examined. Two-year field experiments were conducted in 2017 and 2018 with three sets of foliar applications (nil Zn as control, foliar Zn alone, and foliar Zn plus pesticides) at the anthesis, milk stage, or both. Compared to the control, grain yield was not affected by foliar Zn application alone or combined with pesticides, while the Zn concentrations and bioavailability substantially increased in the whole-grain, bran, and flour irrespective of spray timing. Yield losses by 28%–39% (2018 vs. 2017) led to 7%–18% and 18%–38% increase of Zn density in grain and flour, respectively. Further, such negative responses were uncoupled by foliar spray of Zn or Zn plus pesticides, and absent from the control plants. Nonetheless, grain Zn biofortification was achieved in both low- and high-yield plants with either Zn spray alone or combined with pesticides. Together with the enhanced Zn bioavailability in grain, bran, and flour, the effectiveness of this combined strategy is validated to biofortify wheat with Zn.