Combining Rice Straw Biochar With Leguminous Cover Crop as Green Manure and Mineral Fertilizer Enhances Soil Microbial Biomass and Rice Yield in South China

Effects of biochar, dual inhibitor, and straw return on maize yield, soil physicochemical properties, and microbial system under fertilization conditions

Introduction

Although fertilizers play an important role in achieving high crop yields, improper nitrogen management and application measures have led to a series of ecological and environmental problems. Optimizing fertilization practices in agriculture is crucial for enhancing crop productivity while ensuring sustainable food production.

Methods

This study aims to explore the effects of different fertilization regimes on crop yield, soil physicochemical properties, and microbial ecosystems. During the maize planting process, five fertilization treatments were applied: no fertilizer (CK); conventional fertilization (U), conventional fertilization with composite biochar (UB), conventional fertilization with urease/nitrification inhibitors (UI/NI), and conventional fertilization with straw return (UST).

Results

The results indicate that maize yield under UI/NI treatment was higher than that under U treatment. The microbial community composition among the fertilization treatments had the same dominant species, but the relative abundance of species varied depending on the fertilization treatment; UB and UI/NI enhanced the role of dominant bacterial populations in the soil, while the UST treatment led to the formation of larger and more complex networks of soil bacterial communities.

Discussion

This study provides scientific and theoretical support for the development and promotion of rational fertilizer application.

Green Manure Rotation Combined with Biochar Application Improves Yield and Economic Stability of Continuous Cropping of Peppers in Southwest China

Crop rotation is widely recognized as a key strategy to mitigate the adverse effects associated with continuous cropping. Recent studies have demonstrated that biochar has a significant potential for preventing and controlling these challenges. However, the ameliorative effects of green manure rotation and biochar application on continuous pepper cultivation in the karst mountainous regions of Southwest China remain largely unexplored. To address this gap, a field experiment was conducted from 2020 to 2023 to investigate the effects of green manure rotation and biochar application on the continuous cropping of peppers. The experiment consisted of five treatments: CK (no green manure and no biochar), WP (winter fallow and conventional pepper production with chemical fertilization), GP (green manure and pepper rotation, the amount of fresh green manure returned to the field was about 15 t·ha-1), WP + B (winter fallow and pepper rotation with 1500 kg·ha-1 of biochar applied during the pepper season), and GP + B (green manure and pepper rotation with 1500 kg·ha-1 of biochar applied during the pepper season, the amount of fresh green manure returned to the field was about 15 t·ha-1). The results showed that all the improved measures (GP, WP + B, GP + B) increased the yield of fresh pepper and dry pepper by 26.97-72.98% and 20.96-65.70%, respectively, and the yield of dry pod pepper increased by 14.69-40.63% and 21.44-73.29% in 2021 to 2023, respectively, and significantly improved the yield stability and sustainability of continuous cropping of peppers compared with WP treatments. In addition, green manure rotation or biochar application alone or in combination enhanced the nutritional quality of pepper fruits by increasing the content of free amino acids (8.62-19.42%), reducing sugars (15.30-34.62%) and vitamin C (26.19-43.52), and decreasing the nitrate content (26.93-40.17%). Furthermore, the application of green manure rotation or biochar alone or in combination significantly improved the absorption of nitrogen (23.73-60.23%), phosphorus (18.12-61.71%), and potassium (20.57-61.48%) nutrients in the continuous cropping of peppers, which contributed to the improvement of fertilizer use efficiency. Notably, GP + B treatment not only improved the yield and quality of continuous cropping peppers but also resulted in higher production value and net income compared to the GP and WP + B treatments. In conclusion, the combination of green manure rotation and biochar application represents an effective strategy for mitigating the challenges of continuous cropping in pepper cultivation within the karst mountainous regions of Southwest China.

Alleviation of cotton growth suppression caused by salinity through biochar is strongly linked to the microbial metabolic potential in saline-alkali soil

Biochar is a typical soil organic amendment; however, there is limited understanding of its impact on the metabolic characteristics of microorganisms in saline-alkaline soil microenvironment, as well as the advantages and disadvantages of plant-microorganism interactions. To elucidate the mechanisms underlying the impact of saline-alkali stress on cotton, a 6-month pot experiment was conducted, involving the sowing of cotton seedlings in saline-alkali soil. Three different biochar application levels were established: 0 % (C0), 1 % (C1), and 2 % (C2). Results indicated that biochar addition improved the biomass of cotton plants, especially under C2 treatment; the dry weight of cotton bolls were 8.15 times that of C0. Biochar application led to a rise in the accumulation of photosynthetic pigments by 8.30-51.89 % and carbohydrates by 7.4-10.7 times, respectively. Moreover, peroxidase (POD) activity, the content of glutathione (GSH), and ascorbic acid (ASA) were elevated by 23.97 %, 118.39 %, and 48.30 % under C2 treatment, respectively. Biochar caused a reduction in Na+ uptake by 8.21-39.47 %, relative electrical conductivity (REC) of plants, and improved K+/Na+ and Ca2+/Na+ ratio indicating that biochar alleviated salinity-caused growth reduction. Additionally, the application of biochar enhanced the absorption intensity of polysaccharide fingerprints in cotton leaves and roots. Two-factor co-occurrence analysis indicated that the key differential metabolites connected to several metabolic pathways were L-phenylalanine, piperidine, L-tryptophan, and allysine. Interestingly, biochar altered the metabolic characteristics of saline-alkali soil, especially related to the biosynthesis and metabolism of amino acids and purine metabolism. In conclusion, this study demonstrates that biochar may be advantageous in saline soil microenvironment; it has a favorable impact on how plants and soil microbial metabolism interact.

Spinach (Spinacia oleracea) as green manure modifies the soil nutrients and microbiota structure for enhanced pepper productivity

Spinach has been suggested as a potential rotation crop for increasing crop yield by enhancing beneficial fungal microbes in continuous monocropping. However, no research on the use of spinach as a green manure has been reported. Thus, we tested the effects of spinach and Korean mustard cultivars (green and red mustards) (10 g pot ^-1) as green manure on soil chemical properties, pepper productivity, and soil microbiome of long-year pepper-monocropped soil. Spinach improved the soil nutrition (e.g., pH, SOM, TN, NH₄⁺, and K), weed suppression, and pepper growth. Spinach had by far the highest fruit yield, over 100% pepper fruit yield increment over the mustard green manures and control. Our study showed that the major influencing factors to cause a shift in both bacterial and fungal community assemblies were soil pH, TC TN, and K. Following green manure amendment Bacillota, especially Clostridium, Bacillus and Sedimentibacter, were enriched, whereas Chloroflexi and Acidobacteriota were reduced. In addition, spinach highly reduced the abundance of Leotiomycetes and Fusarium but enriched Papiliotrema. FAPROTAX and FUNGuild analysis revealed that predicted functional profiles of bacterial and fungal communities in spinach-amended soil were changed. Spinach-treated soil was differentially abundant in function related to hydrocarbon degradation and functional guilds of symbiotrophs and ectomycorrhizal. This study contributes significantly to our understanding of how the soil fertility and soil microbiome alteration via spinach green manure application as a pre-plant soil treatment might help alleviate continuous cropping obstacles.