Agronomy

Drought can alter plant nutrient constraints, yet it remains uncertain whether macronutrient limitation hierarchies primarily reflect intrinsic responses or can be reshaped by targeted treatments. In a pot experiment with maize (Zea mays L.), we tested elemental sulfur (ES) and salicylic acid (SA) applied either as foliar sprays or soil amendments under two soil water regimes (30% vs. 60% field water capacity, FWC). Six treatments were evaluated (control, ES-foliar, SA-foliar, SA-soil, ES-soil, and ES + SA-soil; n = 72). Regression tree analysis of data indicated sulfur-potassium co-dominance under drought (24.6% importance each; R² = 0.914), while untreated controls showed nitrogen dominance (27.1%), confirming the S-K pattern is treatment-mediated. Under optimal irrigation (FWC 60%), nutrient importance was balanced across treatments (N, P, K, S; ~22–23%; R² = 0.991). ES + SA applied to soil produced the greatest drought tolerance, increasing dry biomass by 56% at FWC 30%, whereas ES-soil maintained favorable N/S ratios (9.64–9.86). Redundancy analysis confirmed that water availability explained 63.4% of nutrient variance and revealed significant Treatment × FWC interactions. These findings reveal that nutrient hierarchies can be strategically manipulated through targeted fertilization, representing a nutrient management approach for enhancing drought tolerance.

Biochar application can alter soil properties and enhance soil quality. However, the effects of the regulatory mechanisms underlying nitrogen fertilizer application on soil physicochemical properties and microbial characteristics remain unclear. We conducted a three-year maize field experiment to investigate the effects of four biochar application rates (0, 8, 16, and 24 t/ha) and three nitrogen fertilizer rates (0, 150, and 300 kg/ha) on soil physicochemical properties, enzyme activities, microbial community structure, and maize yield. In the 0–20 cm soil layer, the combined application of biochar and nitrogen fertilizer significantly increased soil porosity (SP) and soil water content (SWC), reduced soil bulk density (SBD), and increased soil organic carbon (SOC) and total nitrogen (TN) levels. Additionally, β-D-cellobiohydrolase and leucine aminopeptidase activities were enhanced, along with nitrogen acquisition potential. The relative abundance of Proteobacteria was highest at a biochar application rate of 16 t/ha. The combined 16 t/ha biochar and 150 kg/ha nitrogen treatment exhibited the highest maize yield. Maize yield was positively correlated with SP, SWC, SOC, and TN. Consequently, the combined application of 16 t/ha biochar and 150 kg/ha nitrogen improved soil physicochemical properties, enhanced soil enzyme activities, regulated key soil microbial taxa, and increased maize yield.

Continuous cropping leads to declines in soil productivity and biodiversity, as well as a deterioration of overall phytosanitary conditions. What if we rotate the intercrops instead of the main crops? In a stationary three-year field experiment, maize was intercropped with Fabaceae (faba bean, crimson and Persian clovers, and blue-flowered alfalfa), Poaceae (winter rye, annual ryegrass, spring barley, and common oat), and Brassicaceae (white mustard, spring oilseed rape, oilseed radish, and spring Camelina) intercrops in separate growing seasons. Fabaceae intercrops developed slowly and competed poorly with weeds. The highest air-dried biomass (ADM) was produced by Persian and crimson clovers (approx. 86 g m⁻²). Intercrops of the Poaceae family, particularly rye and oats, as well as ryegrass, which was the most productive at 200 g m⁻² ADM, germinated faster and competed effectively with weeds. Brassicaceae intercrops also developed rapidly, especially mustard, Camelina, and radish (the most productive 206 g m⁻² ADM). Most intercrops competed with maize and reduced its biomass productivity; however, their competitive effects were weaker than those of weeds. A strong negative correlation between maize and weed biomass was detected (max. r = −0.946; p < 0.01). Complex evaluation index (CEI) showed that the crimson clover–annual ryegrass–spring oilseed rape rotation (CC-AR-SR) was the most productive and was effective in suppressing major weeds Echinochloa crus-galli, Chenopodium album, Polygonum lapathifolium, and Cirsium arvense, less competitive with maize (CEI 4.82), and can be used as an Integrated Pest Management tool.