Diversifying crop rotation increases food production, reduces net greenhouse gas emissions and improves soil health

Feeding a growing global population with nutritious food while safeguarding environmental quality is a major challenge, especially in regions with limited resources. Conventional intensification since the Green Revolution has boosted yields but increased greenhouse gas (GHG) emissions and degraded ecosystems, exemplified in China by large increases in fertilizer use and food system GHG emissions. Diversified and integrated farming systems, including rotations with cash crops and legumes, are proposed to reconcile yield, environmental footprint, and soil health while meeting changing dietary demands and improving farmer income. However, evidence remains limited on whether cash-crop and legume-based diversification can simultaneously increase food production, reduce GHG emissions, and improve soil health at the system level. This study addressed these gaps via a 6-year field experiment in the North China Plain (dominated by winter wheat–summer maize double cropping) to comprehensively evaluate diversified rotations for productivity, GHG balance, soil health, and economic outcomes, testing the hypotheses that cash-crop diversification increases farm income without yield penalties, legume diversification reduces field-scale GHG emissions, and integrated diversified rotations deliver joint gains in yield, emissions mitigation, and soil health.

Prior work shows that integrated and diversified crop systems can increase resilience, broaden product portfolios (food, feed, fiber, biofuels), and improve socio-economic outcomes. Global analyses highlight substantial GHG contributions from crop production and the environmental costs of heavy agrochemical reliance. Studies from North America, Europe, Africa, and China have reported that rotational diversification can increase yields, reduce sensitivity to adverse weather, and substitute for high fertilizer inputs, often improving system robustness. Nonetheless, quantitative, multi-metric evidence on cash-crop and legume diversification achieving joint goals of higher food output, reduced environmental footprint, and enhanced soil health under intensive double-cropping systems like the North China Plain remains scarce, motivating the present comprehensive field assessment.

Study site and design: A field experiment was conducted from October 2016 to October 2022 at the Luancheng Agro-Ecosystem Station (Hebei Province; 37°50′N, 114°40′E), representative of North China Plain conditions (warm temperate monsoon climate; mean annual T ≈ 14.7 °C; precipitation ≈ 472 mm). Soils are loam with sandy loam surface, transitioning to light/medium loam and light clay with depth. Baseline (0–10 cm) pH 7.6, SOC 11.5 g kg⁻¹, TN 1.06 g kg⁻¹. Rotations and crops: Six systems were tested: control winter wheat–summer maize (WM; 1-year cycle), and five diversified 2-year cycles: sweet potato→WM (SpWM), peanut–WM (PWM), soybean–WM (SWM), ryegrass–sorghum–WM (RSWM), and spring maize→WM (SmWM). Eight crops were involved: winter wheat, summer maize, spring maize; peanut, soybean; sweet potato; ryegrass, sorghum. Some diversified cycles included fallow during non-WM years. Each rotation had three replicates (18 plots total) in a randomized complete block; cycles repeated on fixed plots for 6 years. Inputs (N, P, K, irrigation, fuel, electricity, pesticides, seed, labor) were recorded; N applied as urea split between basal (incorporated) and topdress at key stages. Residues from WM years were returned to soil. Measurements and calculations: - Productivity: Crop yields measured at maturity (standardized moisture contents). Equivalent yield (to wheat) computed as yield×(price_i/price_wheat) per year; economic benefit (net income) as yield×price (CPI-adjusted to 2008) minus costs; protein yield as yield×crop-specific protein concentration. - GHG fluxes: Soil N₂O and CH₄ measured weekly (more frequently after fertilization/rain) using static chambers and GC (FID for CH₄, µECD for N₂O). Fluxes integrated to seasonal/annual totals via linear interpolation; GWP using IPCC factors (N₂O×273, CH₄×27). Indirect emissions (life cycle) from manufacturing/transport of inputs (fertilizers, pesticides, diesel, electricity) calculated using published emission factors. Net GHG emissions = indirect + direct (GWP_N₂O+CH₄) − soil C sequestration. - Soil C stocks: SOC measured at 0–90 cm (0–10, 10–20, 20–30, 30–50, 50–70, 70–90 cm) after each harvest; bulk density measured for stock calculations. Annual ΔSOC converted to CO₂-eq. - Soil physicochemical and biological indicators: At 0–20 cm in Oct 2016 and Oct 2022 measured pH, bulk density, water content, TN, DOC, NO₃⁻-N, NH₄⁺-N, available P, microbial biomass C and N (fumigation–extraction). Soil health scored using the Cornell Soil Health Assessment (CSHA) framework; indicators normalized and integrated via PCA-derived weighting. - Microbial communities: 16S rRNA (V3–V4; 515F/806R) and ITS1 amplicon sequencing (Illumina MiSeq). OTUs clustered at 97% similarity (QIIME/UPARSE) and assigned via SILVA/UNITE. Alpha diversity indices (Shannon, Chao1, ACE, richness, etc.) computed; redundancy analysis (RDA) related communities to soil properties. - Statistics: Normality (Kolmogorov–Smirnov), one-way ANOVA with LSD post-hoc (p<0.05), Pearson correlations, PCA, visualizations in R. CPI adjustments for price normalization; currency conversion $1=6.95 CNY (May 2023).

- System productivity and income: • Equivalent yield: SpWM increased annual equivalent yield by 38% vs WM (WM baseline 13,185 kg ha⁻¹ yr⁻¹). SmWM (all cereals) decreased equivalent yield by 16%. • Net income: SpWM increased by 60%; PWM and SWM increased by 13–22% (P<0.05) vs WM. • Protein yield: Highest in RSWM (2274 kg ha⁻¹ yr⁻¹) and SWM (1883 kg ha⁻¹ yr⁻¹), 8–31% higher than WM; SmWM decreased protein yield by 23%. • Carryover effects: When WM followed non-cereal preceding crops, grain yield, net income, and protein yield of WM increased by 26–32%, 39–46%, and 25–29%, respectively, vs continuous WM. - GHG emissions and carbon: • N₂O emissions (annual): WM 8.9±1.0 kg N ha⁻¹; reductions of 30% (PWM), 42% (SWM), 49% (SpWM). • CH₄: All systems were net sinks; diversified rotations increased sink strength by 33–76% over WM. • Direct GWP (N₂O+CH₄): WM highest at 3764 kg CO₂-eq ha⁻¹ yr⁻¹; reduced by 22% (RSWM), 19% (SmWM), 32% (PWM), 43% (SWM), 51% (SpWM). • Indirect emissions: WM 8802 kg CO₂-eq ha⁻¹ yr⁻¹; 34–41% lower in SpWM, PWM, SWM, SmWM. • SOC sequestration (0–90 cm): Highest in PWM (2.03 t C ha⁻¹ yr⁻¹), then SWM (1.91), SpWM (1.44); cereal-heavy systems and WM much lower (0.21–0.69). SOC increases in diversified rotations offset total GHG emissions by 75–89% (SpWM, PWM, SWM) vs 7–21% (SmWM, RSWM, WM). • Net GHG: WM 10,025 kg CO₂-eq ha⁻¹ yr⁻¹; SpWM, SWM, PWM reduced net GHG by 83%, 90%, and 92%, respectively (P<0.05). - Soil health and microbiome: • CSHA soil health scores (2022): WM 33.2; PWM 59.5, SWM 56.8, SpWM 52.9 (41–59% higher than WM). PCA of indicators explained 70.5% variance (PC1=51.1%, PC2=19.4%). • Indicator shifts: PWM soils had +6.5% SOC, +29.7% DOC, but lower TN (−5.7%) and AP (−15.4%) vs WM, consistent with 41% less N fertilizer use and improved nutrient use efficiency. RSWM had low SOC/DOC but highest MBC due to forage removal stimulating microbial activity. • Microbial diversity: Shannon index increased by 7–10% in SpWM, PWM, SWM from 2016 to 2022; no change in WM, SmWM, RSWM. Legume rotations increased bacterial OTU richness and fungal Shannon, Chao1, richness (P<0.05). Overall increases in Chao1, ACE, richness after 6 years in SpWM, PWM, SWM vs cereal monocultures. • RDA: Bacterial communities in SpWM, PWM, SWM associated with SOC and AP; WM/SmWM/RSWM associated with TN and MBC. Fungal communities in SpWM, PWM, SWM associated with SOC, pH, DOC. - Multi-functionality (CEI): WM had lowest CEI (0.19); SpWM 0.81, PWM 0.75, SWM 0.69; SmWM and RSWM 0.25–0.29. Soil health positively correlated with yield (r=0.79), economic benefit (r=0.85), nutrition score (r=0.90), carbon sequestration (r=0.79), biodiversity (r=0.67), and negatively with net GHG emissions (r=−0.83). - Scaling implications: North China Plain-wide adoption could reduce net CO₂-eq by 106.8±31.7 Mt yr⁻¹ (~5.6% of China’s food system emissions in 2020), cut synthetic N fertilizer by 3.6 Mt, increase farmer net income by ~20% (~84 billion CNY), raise soil health scores by 45%, increase WM cereal yields by 32% when following alternative crops, and generate ~36.1 Mt additional straw biomass annually.

The study confirms that diversifying the wheat–maize double-cropping system with sweet potato and legumes can simultaneously enhance food production and nutrition (grain and protein yields), reduce GHG emissions (direct and indirect) through lower fertilizer requirements and increased SOC sequestration, and improve soil health and microbial diversity. Positive carryover effects from non-cereal precrops increased subsequent WM yields and income, demonstrating rotation benefits beyond within-year gains. Mechanistically, legumes reduce external N inputs—diminishing N₂O emissions—and, together with sweet potato, stimulate microbial growth, carbon use efficiency, and stabilization of mineral-associated SOC. Alternation of shallow- and deep-rooted crops improves rooting profiles, porosity, aggregate stability, and nutrient use efficiency, reducing leaching and enhancing SOC storage. Diversified residues and root exudates increase microbial alpha diversity and shift community composition toward functions that support C cycling and plant growth. Considering the depth-resolved SOC measurements (to 90 cm), the study highlights substantial subsoil C contributions to mitigation. The integrated performance (high CEI) and strong correlations between soil health and agronomic/economic outcomes indicate that soil-centered diversification strategies provide broad ecosystem service gains and climate co-benefits. At scale in the North China Plain, diversified rotations could meaningfully reduce national food-system emissions and improve farmer livelihoods, aligning with China’s policy goals on legumes promotion, fertilizer reduction, and agricultural decarbonization.

Diversifying crop rotations in the North China Plain by integrating cash crops (sweet potato) and legumes (peanut, soybean) into the wheat–maize system delivers joint gains in productivity, profitability, climate mitigation, and soil health. Legume- and sweet potato-based rotations increased equivalent and protein yields, boosted farmer income, reduced direct and indirect GHG emissions, and substantially enhanced SOC sequestration and soil health scores while enriching microbial diversity. The comprehensive evaluation index confirmed superior multi-functionality of diversified rotations compared with cereal-dominated systems. Policy and farm-level adoption of diversified rotations should be prioritized, with rotation design tailored to local agro-environmental conditions to balance production with ecosystem services. Future research should expand multi-location, longer-term monitoring to capture spatiotemporal variability and extreme weather impacts, refine optimization of crop configurations and input management, and further elucidate microbial mechanisms underpinning soil health and carbon stabilization.

Findings are based on a single research station representative of the North China Plain over six years. Results may be influenced by site-specific conditions, management, and interannual weather variability. Diversified rotations included fallow periods in some years, affecting temporal comparability. Broader generalization requires multi-location, longer-term experiments across varying climates and soils to reduce uncertainties associated with spatial heterogeneity and climate extremes. Emissions beyond the farm gate (e.g., transport/marketing) were outside the system boundary.