Manure Beats Commercial Organic Fertilizer in Drought-Hit Wheat Fields

On the wind-scoured Loess Plateau of northern China, where rainfed winter wheat survives on whatever precipitation falls between autumn sowing and summer harvest, a long-running field experiment has delivered a deceptively simple verdict with far-reaching consequences: not all organic fertilizers are created equal. A team of researchers led by Yanrong Lin and Xiaoli Chen of Northwest A&F University reports in the Journal of Agriculture and Food Research that, under identical total nitrogen inputs, substituting a quarter of chemical fertilizer nitrogen with pig manure outperformed both pure chemical fertilization and substitution with commercial organic fertilizer across four consecutive growing seasons. The advantage was most dramatic in drought years, precisely where rainfed agriculture is most fragile.

The experiment, established in 2017 at the Heyang Wheat-Maize Experimental Station in Shaanxi Province, sits in a warm-temperate semiarid monsoon climate averaging 573.89 millimeters of annual precipitation. The team tracked four treatments from 2021 to 2025: no nitrogen input, conventional chemical nitrogen at 180 kilograms per hectare, and two regimes in which 25 percent of that nitrogen was replaced with either pig manure or commercial organic fertilizer. All plots received equal phosphorus and potassium, and the crop, cultivar Jinmai 47, was grown without irrigation under no-till management, exactly as local smallholders do.

What makes the study unusual is its insistence that fertilizer source matters, not merely fertilizer quantity. Pig manure and commercial organic product differ in raw material composition, maturity, carbon-to-nitrogen ratio, decomposition rate, and the timing of nutrient release. Those differences, the researchers hypothesized, would ripple through the soil profile, altering how water and nitrate are stored and distributed, how wheat roots explore the soil, and ultimately how yield responds when the sky withholds or delivers rain. To test this, the team classified each season by a drought index: 2021–2022 and 2023–2024 were wet, 2022–2023 normal, and 2024–2025 dry.

The yield data tell a striking story. Nitrogen application lifted grain yields by 44 to 83 percent over unfertilized controls, but the organic substitutions consistently beat chemical fertilizer alone. In the dry year, manure substitution raised yield by 10.32 percent, net income by 32.19 percent, and the benefit–cost ratio by 10.68 percent relative to chemical nitrogen. Manure also produced the highest yields and returns in normal and wet years, reaching 6,395 kilograms per hectare and 9,021 CNY per hectare in wet seasons. In drought, when chemical-only plots fell to 3,674 kilograms per hectare, manure plots held at 4,097 — a buffer against climatic shock that commercial organic fertilizer only partially matched.

Beneath the surface, the mechanisms were physical and measurable. Manure substitution increased mean weight diameter of soil aggregates and water-stable macroaggregate content while lowering bulk density and fractal dimension, indicators of a looser, better-connected pore network. In the top 20 centimeters, manure boosted soil organic matter by 20.27 percent and total nitrogen by 17.57 percent over chemical fertilization, and across the 0–60 centimeter profile the gains reached 21.55 and 19.22 percent. Better aggregates mean better infiltration and water-holding capacity — a critical asset when precipitation arrives in stingy, erratic pulses.

The vertical distribution of water and nitrate revealed perhaps the most intriguing source-specific signature. Both organic treatments enhanced deep soil water storage at 130–200 centimeters, but manure plots accumulated less nitrate-nitrogen than commercial-fertilizer plots across the 0–200 centimeter profile, with a 6.62 percent reduction in the deep 100–200 centimeter layer. The researchers link this to higher root length density under manure in the measured 0–100 centimeter zone: more roots occupying the upper profile potentially intercept more nitrate before it leaches downward. In a region where deep nitrate accumulation signals both wasted fertilizer and groundwater risk, that asymmetry matters.

Root architecture itself responded to the fertilizer regime. Nitrogen application of any kind increased root length density by 28.17 percent and root weight density by 43.16 percent over unfertilized plots, with organic treatments showing generally higher values than chemical alone. Specific root length, a measure of root fineness, fell by more than half in the dry year compared with wet and normal years, reflecting the crop’s struggle to build absorptive tissue when water is scarce. Precipitation year type shaped everything: root length and weight densities rose 22–64 percent and 33–82 percent respectively in wetter seasons.

To move beyond single indicators, the team deployed two integrative tools. A soil quality index, built from principal component analysis of bulk density, porosity, aggregate stability, organic matter, total nitrogen, and pH, ranked the treatments manure > commercial organic > chemical > no nitrogen, with manure raising the index 73.46 percent over the unfertilized control. A coupling coordination degree model then quantified how well the soil-quality system moved in lockstep with the production-benefit system of yield, net income, and benefit–cost ratio. Coordination exceeded 0.5 — high coordination — under all fertilized treatments except in drought, and manure substitution achieved the highest coordination values, including 0.86 in wet years and a relative advantage over chemical fertilization even in the dry year.

Structural equation modeling tied the threads together. Precipitation acted directly on soil properties but also indirectly by promoting root development, while nitrogen fertilization enhanced production mainly by improving soil physicochemical conditions and root traits. Under manure, yield correlated positively with the soil quality index, coordination degree, net income, and benefit–cost ratio, suggesting the treatment synchronized structural and functional soil improvement with economic output. Notably, soil quality improvements did not always translate into higher water-use efficiency — that conversion depended on the synchrony between nutrient release, root uptake, and precipitation timing, a nuance the authors flag honestly, noting that carbon quality and decomposition dynamics were not directly measured.

The practical message for dryland agriculture is pointed. Where manure is locally available and transport costs are manageable, substituting 25 percent of mineral nitrogen with manure emerges as the most suitable strategy for rainfed winter wheat on the Loess Plateau, offering superior soil rebuilding, deeper water retention, reduced deep nitrate storage, and the strongest drought insurance. The authors caution that long-term environmental effects and the microbial mechanisms behind these responses remain to be fully evaluated. But in an era of intensifying precipitation volatility, the finding that the source of organic nitrogen — not just its amount — governs whether soil improvement becomes farmer income is a lesson that will travel well beyond the yellow earth of Shaanxi.

Subject of Research: Effects of organic fertilizer source on soil quality and winter wheat production in dryland farming

Article Title: Organic fertilizer source regulates soil quality–production coordination in dryland winter wheat on the Loess Plateau

Article References: Lin, Y., Han, Y., Li, Z., Zhang, X., Luo, X., Zhang, Y., Qiang, B., Wang, J., Zhao, X., Liu, E., Ren, X., & Chen, X. (2026). Organic fertilizer source regulates soil quality–production coordination in dryland winter wheat on the Loess Plateau. Journal of Agriculture and Food Research, Article 103366. https://doi.org/10.1016/j.jafr.2026.103366

Image Credits: AI Generated

DOI: 10.1016/j.jafr.2026.103366

Keywords: dryland agriculture, winter wheat, organic fertilizer, manure substitution, soil quality index, Loess Plateau, nitrogen management, water use efficiency, soil aggregates, drought resilience, coupling coordination, rainfed farming