Wheat Yield Response to Organic Fertilisers Depends on Drought Timing in a Sandy Soil

ABSTRACT Organic fertilisers enhance crop drought resilience by improving nitrogen (N) and phosphorus (P) use efficiency and soil‐plant water relations. However, the underlying mechanisms governing their effects across different drought timings in wheat under sandy soils remain unclear. This 120‐day controlled‐environment experiment assessed how compost, sheep manure, and their combinations applied at 25 g kg − 1 ameliorate wheat yield under drought (35%WHC; −10 kPa) imposed at two timings: early‐ (tillering, 20 DAS) and late‐stage drought (heading, 60 DAS) in a sandy soil. The manure alone and combined amendments (CM 50 SM 50 ≈ CM 25 SM 75, ≈CM 75 SM 25 > SM 100 ) retained more soil moisture compared to the compost alone treatment. Compared with the control, compost and the half‐half‐blend with manure increased grain yield by up to 2.3‐fold under early drought and only 1.4‐fold under late drought. The compost‐rich treatments increased root N uptake by 2.6–3.5 fold and sustained grain‐based N utilisation efficiency during early drought. Manure‐rich treatments showed higher P uptake, but P utilisation efficiency remained lower compared with the compost‐rich treatments across drought timings. During early drought, half‐half‐blend increased soil organic carbon by 90%, and plant available water by 21% over the unamended control. Compost‐rich treatments improved microbial N mineralisation under early drought by increasing microbial biomass nitrogen by 8.1‐fold and nitrate‐N by 2.4‐fold. The Partial Least Squares Path Modelling analysis confirmed the relationship between field capacity, microbial activity, nutrient availability, and grain yield. Oveall, manure‐rich treatments enhanced moisture retention, while compost‐rich treatments balanced nutrient acquisition and utilisation by rapid P supply from manure with sustained N mineralisation from compost, enhancing wheat resilience more under early than late drought. Therefore, we recommend compost and manure combination as a potential approach to increase dryland wheat yield during early‐stage droughts in sandy soils.