Zinc (Zn) deficiency is a global nutritional problem that is reduced through agronomic biofortification. In the current study, the effects of foliar spraying of exogenous ZnSO₄·7H₂O (0.2% in Quzhou and 0.3% in Licheng, w/v) and/or sucrose (10.0%, w/v) on maize (Zea mays L.) agronomic traits; concentrations of Zn, iron (Fe), calcium (Ca), total phosphorus (P), phytic acid (PA) P, carbon (C), and nitrogen (N); C/N ratios; and Zn and Fe bioavailability (as evaluated by molar ratios of PA/Zn, PA × Ca/Zn, PA/Fe and PA × Ca/Fe) in maize grains were studied under field conditions for two years at two experimental locations. The results confirmed that there were no significant differences in maize agronomic traits following the various foliar treatments. Compared with the control treatment of foliar spraying with deionized water, foliar applications of Zn alone or combined with sucrose significantly increased maize grain Zn concentrations by 29.2–58.3% in Quzhou (from 18.4–19.9 to 25.2–29.6 mg/kg) and by 39.8–47.8% in Licheng (from 24.9 to 34.8–36.8 mg/kg), as well as its bioavailability. No significant differences were found between the foliar spraying of deionized water and sucrose, and between Zn-only and “sucrose + Zn” at each N application rate and across different N application rates and experimental sites. Similar results were observed for maize grain Fe concentrations and bioavailability, but the Fe concentration increased to a smaller extent than Zn. Foliar Zn spraying alone or with sucrose increased maize grain Fe concentrations by 4.7–28.4% in Quzhou (from 13.4–17.1 to 15.2–18.5 mg/kg) and by 15.4–25.0% in Licheng (from 24.0 to 27.7–30.0 mg/kg). Iron concentrations were significantly and positively correlated with Zn at each N application rate and across different N application rates and experimental locations, indicating that foliar Zn spraying facilitated the transport of endogenous Fe to maize grains. Therefore, foliar Zn spraying increased the Zn concentration and bioavailability in maize grains irrespective of foliar sucrose supply while also improving Fe concentrations and bioavailability to some extent. This is a promising agricultural practice for simultaneous Zn and Fe biofortification in maize grains, i.e., “killing two birds with one stone”.

Rational crop community structure plays an important role in maximizing the intercropping yield advantage. Effects of increasing maize densities in maize (Zea mays L.)/peanut (Arachis hypogaea L.) intercropping on yields and other agronomic traits, and the community stability of productivity were conducted across three different experimental sites. There were significant and positive correlations between maize densities and both maize grain/biomass yields and corresponding partial land equivalent ratios (LERs) across all three locations; but grain/biomass yields and partial LERs of peanut were all negatively correlated with maize densities in each or across all locations. LERs of grain yields averaged over three locations ranged from 0.89 to 0.98, while LERs of biomass yields ranged from 0.94 to 1.09 (>1.0 except for the maize inter-plant distance of 27 cm), indicating the intercropping advantage on biomass yields but not grain yields. Peanut had significantly lower kernel harvest indexes than those in monoculture. Excessive narrowing maize inter-plant distances reduced the community stability of productivity severely (especially for maize and total LERs) and are more likely to lead to abnormal maize and peanut plants. Therefore, a rational increase of maize densities in intercropping is suggested to keep the balance between maize and peanut and the comprehensive yield advantage.

Rational regulation of phosphorus (P) use in the soil–rhizosphere–plant system is challenging in the development of sustainable, intensive, and healthy agriculture. Rational maize (Zea mays L.) based intercropping with legumes/oilseed rape across six experimental sites from 2008 to 2017 proved advantageous over monoculture in terms of both maize biomass production and P uptake. The partial land equivalent ratio (PLER) for P uptake by intercropped maize averaged from 0.58 to 0.92, which was significantly higher than that for biomass production (0.51–0.78), indicating that the advantage of P acquisition by intercropped maize was superior to that of biomass accumulation. It was the excessive accumulation of P in intercropped maize compared to monoculture, especially higher P concentrations in grains that led to the superior P acquisition advantage and luxury absorption of P. P concentrations in maize grains were significantly increased from 1.89–2.91 mg kg⁻¹ in monoculture to 2.09–3.65 mg kg⁻¹, in intercropping, by 8.3%–25.5%. The plant internal P use efficiency of maize was significantly decreased from the initial 411.7–775.7 kg kg⁻¹ in monoculture to 345.7–710.4 kg kg⁻¹ in intercropping by 4.9%–16.0%, and 100 kg maize grain P quantities were significantly increased from 0.25–0.46 kg to 0.27–0.54 kg by 7.0%–17.4%. Rational fertilizer P input maximized maize yields and P use without decreasing the interspecific ecological advantages and harvest indexes of grain yields and P. These findings promoted better understanding of P allocation status within maize plants, and yield and P acquisition advantages through the exploitation of the biological potential of plants for the efficient utilization of P resources in diverse species combinations.

The composition and form of selenium in the soil have significant effects on the selenium content of crops. In this study, we investigated the selenium absorption pathway in plants by studying the interaction between nitrogen fertilizer and soil selenium. Our results showed that the selenium concentration enrichment factors (CEF) varied within the same region due to nitrogen fertilizer application, where they ranged from 1.33 to 5.02. The soil selenium flow coefficient (mobility factor, MF) increased with higher nitrogen application rates. The sum of the MF values for each soil layer treated with nitrogen application rates of 192 kg hm⁻² and 240 kg hm⁻² was 0.70, which was 64% higher than that for the control group with no nitrogen application. In the 0–20 cm soil layer, the highest summed water-soluble and exchangeable selenium and relative percentage of total selenium (12.45%) was observed at a nitrogen application rate of 240 kg hm⁻². In the 20–40 cm soil layer, the highest relative percentage content of water-soluble and exchangeable selenium and total selenium (12.66%) was observed at a nitrogen application rate of 192 kg hm⁻². Experimental treatment of black wheat with various concentrations of sodium selenite showed that selenium treatment at 50 μmol L⁻¹ significantly increased the reduced glutathione (GSH) levels in the leaves and roots of seedlings, where the GSH contents increased by 155.4% in the leaves and by 91.5% in the roots. Further analysis of the soil–black wheat system showed that nitrogen application in selenium-rich areas affected the soil selenium flow coefficient and morphological composition, thereby changing the enrichment coefficient for leaves (0.823), transport capacity from leaves to grains (–0.530), and enrichment coefficient for roots (0.38). These changes ultimately affected the selenium concentration in the grains of black wheat.

Plant growth regulators (PGRs) enhance crop stress resistance but their roles in microbial-mediated phosphorus cycling within intercropping systems are unclear. Thus, We conducted a two-year field study using corn (Zea mays L. cv. Denghai 605) and soybean (Glycine max L. cv. Hedou 22) in fluvisols and luvisols soil according to World Reference Base for Soil Resources (WRB) standard. Under a 4-row corn and 6-row soybean strip intercropping system, three treatments were applied: a water control (CK), and two plant growth regulators—T1 (EC: ethephon [300 mg/L] + cycocel [2 g/L]) and T2 (ED: ethephon [300 mg/L] + 2-Diethyl aminoethyl hexanoate [10 mg/L]). Foliar applications were administered at the V7 stage (seventh leaf) of intercropped corn plants to assess how foliar-applied PGRs (T1/T2) modulated the soil phosphorus availability, microbial communities, and functional genes in maize intercropping systems. PGRs increased the soil organic phosphorus and available phosphorus contents, and alkaline phosphatase activity, but not total phosphorus. PGRs declined the α-diversity in fluvisols soil but increased the α-diversity in luvisols soil. The major taxa changed from Actinobacteria (CK) to Proteobacteria (T1) and Saccharibacteria (T2) in fluvisols soil, and from Actinobacteria/Gemmatimonadetes (CK) to Saccharibacteria (T1) and Acidobacteria (T2) in luvisols soil. Functional gene dynamics indicated soil-specific regulation, where fluvisols soil harbored more phoD (organic phosphorus mineralization) and relA (polyphosphate degradation) genes, whereas phnP gene dominated in luvisols soil. T1 stimulated organic phosphorus mineralization and inorganic phosphorus solubilization in fluvisols soil, upregulating regulation genes, and T2 enhanced polyphosphate synthesis and transport gene expression in luvisols soil. Proteobacteria, Nitrospirae, and Chloroflexi were positively correlated with organic phosphorus mineralization and polyphosphate cycling genes, whereas Bacteroidetes and Verrucomicrobia correlated with available potassium (AP), total phosphorus (TP), and alkaline phosphatase (ALP) activity. Thus, PGRs activated soil phosphorus by restructuring soil type-dependent microbial functional networks, connecting PGRs-induced shifts with microbial phosphorus cycling mechanisms. These findings facilitate the targeted use of PGRs to optimize microbial-driven phosphorus efficiency in strategies for sustainable phosphorus management in diverse agricultural soils.

Agronomy practices aimed at wheat (Triticum aestivum L.) grain Zn biofortification are important to alleviate Zn deficiency in humans, especially for those resource-poor people owing to subsistence on diets dominated by cereal-based foods with low concentrations and bioavailability of Zn. To promote understanding of source-sink flow processes affecting biofortification of wheat with Zn, effects of different source/sink manipulations on grain Zn accumulation by wheat were examined in pot and field at two locations. Treatments included foliar applications of deionized water, sucrose, ZnSO₄, sucrose + Zn, defoliation, spike shading or partial removal of spikes. Results showed sucrose + Zn significantly increased grain Zn concentration more than Zn alone. Grain Zn concentration with sucrose + Zn averaged 66 mg kg^-1 for ‘Kenong 9204’ and 59 mg kg^-1 for ‘Liangxing 99’ in pot, and ranged from 42 to 58 mg kg^-1 for ‘Liangxing 99’, ‘Jinan 17’, ‘Jimai 20’, ‘Jimai 22’, and ‘Luyuan 502’ under field, approaching the field-grown target 60 mg kg^-1 proposed by World Health Organization. Molar ratios of phytic acid/Zn and phytic acid × Ca/Zn of ‘Jinan 17’, ‘Jimai 20’ or ‘Luyuan 502’ with sucrose + Zn were reduced to be < 15 and < 200, respectively, suggesting higher Zn bioavailability. Defoliation or spike shading decreased grain weight, Zn concentration and content. It is concluded that grain Zn accumulation of wheat can be affected by the source-sink relationship of Zn and/or carbohydrate, and the foliar spray ‘sucrose + Zn’ is recommended for increasing concentration and bioavailability of Zn in wheat grains.