Biogas Fertilizer Boosts Soil Microbes and Apple Quality on the Loess Plateau

On the dusty, wind-scoured terraces of China’s semiarid Loess Plateau, apple growers have long wrestled with a stubborn paradox: the region’s deep, well-drained loess soils are ideal for fruit trees, yet decades of intensive cultivation and heavy chemical fertilization have left many orchards degraded, compacted, and starved of organic matter. Now, a three-year field experiment conducted by researchers at Gansu Agricultural University suggests that a humble byproduct of rural waste management—biogas fertilizer, the nutrient-rich slurry left over after anaerobic digestion—may offer a way to rebuild these tired soils from the ground up, with measurable benefits that ripple upward through soil microbes, tree physiology, and ultimately the apples themselves.

The study, published in BMC Plant Biology, was led by Baozhen Zeng, Yongjuan Cheng, and colleagues from the College of Horticulture at Gansu Agricultural University in Lanzhou, with Juan Mao serving as corresponding author. The team set out to answer a deceptively simple question: how do different fertilization schemes, particularly those incorporating biogas fertilizer, shape the physical and chemical properties of orchard soil, the structure and function of its microbial communities, the physiological performance of apple trees, and the quality of the fruit they bear? Because the Loess Plateau is one of China’s most important apple-producing regions, the answer carries weight far beyond a handful of experimental plots.

The researchers ran their field experiment over three growing seasons, comparing several fertilization regimes that differed in whether and how much biogas fertilizer was applied. The apple variety under study was ‘Yanfu 3’, a cultivar widely grown in the region. The team then tracked an unusually comprehensive suite of variables: soil water-holding capacity, soil organic matter, nutrient availability, cation exchange capacity, and pH; the composition and diversity of the soil microbial community; leaf nutrient accumulation and photosynthetic performance; and, finally, fruit size, colouration, sugar composition, and bioactive compounds. Supplementary analyses included rarefaction and rank-abundance curves, principal component analysis, non-metric multidimensional scaling with PERMANOVA testing, and detailed vertical profiles of macro- and micronutrients—nitrogen, phosphorus, potassium, iron, manganese, zinc, and copper—across soil layers and years.

The headline finding is that fertilization regimes incorporating biogas fertilizer were consistently associated with better soil conditions. Soils receiving biogas showed increased water-holding capacity—a critical trait in a semiarid region where every millimetre of stored moisture counts—alongside higher soil organic matter content, greater nutrient availability, and improved cation exchange capacity, the soil’s ability to hold onto positively charged nutrients such as potassium, ammonium, calcium, and magnesium. Perhaps just as importantly, biogas-amended soils maintained a pH within the range of roughly 6.5 to 7.5, the window in which most nutrients remain maximally available to tree roots. In acidified or alkalized soils, nutrients can become chemically locked away even when total reserves are ample; keeping pH in the neutral band is one of the quiet achievements of good organic management.

Depth mattered. The beneficial effects of biogas incorporation were most pronounced in the top 0 to 20 centimetres of soil, the layer where apple trees concentrate much of their fine-root activity and where most microbial biomass resides. The effects also became more evident as application rates increased, pointing to a dose-responsive relationship rather than a simple yes-or-no effect. For growers, this suggests that the surface layer—often the most vulnerable to erosion, drying, and nutrient depletion—is precisely where organic amendments deliver their greatest returns.

Beneath the visible improvements in soil chemistry, the study documented a parallel transformation in the soil’s living community. Biogas-fertilized plots showed shifts in microbial community composition and diversity, with a notable enrichment of functional groups involved in organic matter decomposition and nutrient cycling. In practical terms, this means the soil microbiome was recalibrated toward organisms that break down complex organic residues and convert them into plant-available forms of nitrogen, phosphorus, and other nutrients. Such communities act as the digestive system of the orchard: when they are abundant and active, organic inputs are efficiently mineralized, and nutrients circulate rather than accumulate in inaccessible forms. The multivariate statistical analyses confirmed that samples from different treatments clustered distinctly, indicating that fertilization regime left a detectable fingerprint on the entire microbial assemblage.

Those below-ground changes translated into above-ground gains. Trees growing in biogas-amended soils accumulated more nutrients in their leaves and showed enhanced photosynthetic performance, the engine that converts sunlight into the sugars and carbon skeletons that build fruit. Leaf nutrient status is a well-established diagnostic of tree health in horticulture, and improved photosynthesis provides the raw material for everything a grower ultimately sells. The chain of causation proposed by the authors runs cleanly from soil to microbe to leaf to fruit: better soil structure and fertility support a more functional microbiome, which supplies nutrients more effectively, which powers the canopy, which feeds the crop.

And the crop responded. Fruit from trees under biogas-inclusive regimes showed improvements in size, colouration, sugar composition, and bioactive compounds—the suite of traits that determine whether an apple commands a premium price at market. Colouration reflects anthocyanin accumulation and light interception within the canopy; sugar composition governs sweetness and flavour balance; and bioactive compounds contribute to nutritional value and storage quality. Among all the regimes tested, the treatment delivering 90 kilograms of biogas fertilizer per tree produced the most favourable overall performance under the experimental conditions, offering growers a concrete starting point for calibrating their own application rates.

The authors are careful to frame their conclusions with appropriate scientific caution. Because the different treatments involved different total nutrient inputs, the observed effects reflect integrated fertilization outcomes rather than the isolated effect of biogas fertilizer itself. In other words, some of the benefit may stem simply from supplying more nutrients in a more balanced form, rather than from any unique property of the biogas slurry. This distinction matters for interpretation, but it does not diminish the practical message: schemes that integrate biogas fertilizer, as applied in this study, outperformed the alternatives across soil, microbial, physiological, and fruit-quality metrics simultaneously.

The broader implications extend into sustainability and circular agriculture. Biogas fertilizer is a product of anaerobic digestion of organic wastes such as manure and crop residues, so integrating it into orchard management closes a nutrient loop: farm waste becomes fuel, and the digested residue returns to the soil as fertilizer. In a semiarid region where soil degradation and low nutrient use efficiency have constrained sustainable productivity, this dual benefit—waste recycling and soil restoration—is especially attractive. The study’s authors position their findings as a basis for optimizing organic fertilization strategies in semiarid apple orchards, and with three years of field data spanning soil physics, microbiology, tree physiology, and fruit chemistry, they have built one of the more complete evidence chains linking what farmers put into the ground with what consumers eventually bite into. For the apple growers of the Loess Plateau, the path to sweeter, redder, larger fruit may run straight through the digester.

Subject of Research: Effects of biogas fertilizer regimes on soil microbial function, tree growth, and fruit quality in semiarid Loess Plateau apple orchards

Article Title: Relationships among different fertilization schemes, soil microbial function, tree growth, and fruit quality in apple orchards on the semiarid Loess Plateau

Article References: Zeng, B., Cheng, Y., Gou, H., Lu, S., Wu, X., Shi, G., Liang, G., Chen, B., & Mao, J. (2026). Relationships among different fertilization schemes, soil microbial function, tree growth, and fruit quality in apple orchards on the semiarid Loess Plateau. BMC Plant Biology. https://doi.org/10.1186/s12870-026-09888-7

Image Credits: AI Generated

DOI: 10.1186/s12870-026-09888-7

Keywords: biogas fertilizer, apple orchards, Loess Plateau, soil microbial community, soil organic matter, fruit quality, photosynthesis, organic fertilization, semiarid agriculture, soil pH, nutrient cycling, BMC Plant Biology