Liming (L) is a common practice to mitigate soil acidification and enhance soil quality and crop productivity. However, in acidic soil, it is not clear how long-term application of lime and nitrogen (N)-based fertilizer affects soil chemical properties, the wheat and maize grain yields (GY), and N-use efficiency (NUE). Thus, to investigate the effects of N-based fertilizations without L (−L) and with L (+L) on wheat and maize GY and NUE through their effects on soil chemical properties, we analyzed a 28-year field experiment in acidic soil under a wheat-maize system in South China. The analysis was carried out between 1991 and 2010 (before L) and between 2011 and 2018 (after L). We categorized the treatments into (1) no fertilizer (C); nitrogen (N); N and phosphorus (NP); N and potassium (NK); N, P and K (NPK); and NPKC_R, NPK and crops residue (C_R) applications (NPKC_R), before L; and (2) C; N−L; N+L; NP−L; NP+L; NK−L; NK+L; NPK−L; NPK+L; NPKC_R−L and NPKC_R+L, after L. The effects of long-term fertilization resulted in lower soil pH by 15%, soil available K (AK) by 19%, P_Olsen by 6%, NO₃⁻-N by 15%, soil organic matter (SOM) by 16%, total N by 16%, and C:N ratio by 13% in −L soil than in +L soil. However, the accumulation of NH₄⁺-N was higher by 40% in −L soil than in +L soil. Wheat and maize GY, N recovery efficiency (RE_N), and N partial factor productivity (PEP_N) were more adversely affected by 8-year fertilizations in −L compared with fertilizations before L and in +L primarily because of the significantly decreased soil pH. Conversely, improvements in wheat and maize yields, RE_N, and PFP_N by 8-year fertilizations in +L were related to increasing soil pH, exchangeable base cations such as Ca²⁺, Mg²⁺, and the alleviated toxicity of Al³⁺. Overall, improvement of GY and NUE from the acidified soil in South China requires the long-term integrated use of fertilizer (NPK), retention of C_R, and the +L (i.e., NPKC_R+L).

A long-term field experiment was carried out (since 2008) for evaluating the effects of different substitution rates of inorganic nitrogen (N) fertilizer by green manure (GM) on yield stability and N balance under double rice cropping system. Treatments included, (1) N₀ (no N fertilizer and no green manure); (2) N₁₀₀ (recommended rate of N fertilizer and no green manure); (3) N₁₀₀-M (recommended rate of N fertilizer and green manure); (4) N₈₀-M (80% of recommended N fertilizer and green manure); (5) N₆₀-M (60% of recommended N fertilizer and green manure); and (6) M (green manure without N fertilization). Results showed that, among all treatments, annual crop yield under N₈₀-M treatment was highest. Crop yield did not show significant differences between N₁₀₀-M and N₈₀-M treatments. Substitution of different N fertilizer rates by GM reduced the yield variability index. Compared to the N₀ treatment, yield variability index of early rice under N₁₀₀-M, N₈₀-M, and N₆₀-M treatments was decreased by 11%, 26%, and 36%, respectively. Compared to the N₀ treatment, yield variability index of late rice was decreased by 12%, 38%, 49%, 47%, and 24% under the N₁₀₀, N₁₀₀-M, N₈₀-M, N₆₀-M, and M treatments, respectively. During period of 2009–2013 and 2014–2018, nitrogen recovery efficiency (NRE) was highest under N₈₀-M treatment and N balance was highest under N₁₀₀ treatment. NRE of all treatments with GM was increased over the time from 2009–2013 to 2014–2018. All treatments with GM showed increasing trend of SOC over the years. Substitution of N fertilizer by GM also increased C inputs and soil C:N ratio compared to the N₁₀₀ and N₀ treatments. Boosted regression model indicated that C input, N uptake and AN were most influencing factors of crop yield. Thus, we concluded that N fertilization rates should be reduced by 20% under GM rotation to attain high yield stability of double rice cropping system through increasing NRE and C inputs.

Cultivation of green manure (GM) crops in intensive cropping systems is important for enhancing crop productivity through soil quality improvement. We investigated yield sustainability, nutrient stocks, nutrient balances and enzyme activities affected by different long-term (1982–2016) green manure rotations in acidic paddy soil in a double-rice cropping system. We selected four treatments from a long-term experiment, including (1) rice-rice-winter fallow as a control treatment (R-R-F), (2) rice-rice-milkvetch (R-R-M), (3) rice-rice-rapeseed (R-R-R), and (4) rice-rice-ryegrass (R-R-G). The results showed that different GM rotations increased grain yield and the sustainable yield index compared with those of the R-R-F treatment. Compared with those of R-R-F, the average grain yield of early rice in R-R-M, R-R-R, and R-R-G increased by 45%, 29%, and 27%, respectively and that of late rice increased by 46%, 28%, and 26%, respectively. Over the years, grain yield increased in all treatments except R-R-F. Green manure also improved the soil chemical properties (SOM and total and available N and P), except soil pH, compared to those of the control treatment. During the 1983–1990 cultivation period, the soil pH of the R-R-M treatment was lower than that of the R-R-F treatment. The addition of green manure did not mitigate the soil acidification caused by the use of inorganic fertilizers. The soil organic matter (SOM), total nitrogen (TN) and total phosphorus (TP) contents and stocks of C, N and P increased over the years. Furthermore, GM significantly increased phosphatase and urease activities and decreased the apparent N and P balances compared with those in the winter fallow treatment. Variance partitioning analysis revealed that soil properties, cropping systems, and climatic factors significantly influenced annual grain yield. Aggregated boosted tree (ABT) analysis quantified the relative influences of the different soil properties on annual grain yield and showed that the relative influences of TN content, SOM, pH, and TP content on annual crop yield were 27.8%, 25.7%, 22.9%, and 20.7%, respectively. In conclusion, GM rotation is beneficial for sustaining high crop yields by improving soil biochemical properties and reducing N and P balances in acidic soil under double- rice cropping systems.

Soil microbial activities are consistently restricted not only by phosphorus availability but also by microbial carbon requirements. Therefore, an incubation experiment was conducted with three soils (QY1, QY2 and QY3) selected on the basis of phosphorus limitation. Results revealed that high N₂O emissions, 17.44 µg kg⁻¹, were measured in phosphorus-deficient soil with addition of glucose. In phosphorus-adequate soils, the peaks of N₂O emission values in the glucose addition treatment were 20.8 µg kg⁻¹ and 24.7 µg kg⁻¹, which were higher than without glucose-added treatments. CH₄ emissions were higher with glucose addition, at 1.9 µg kg⁻¹ in phosphorus-deficient soil and 1.52 µg kg⁻¹ and 2.6 µg kg⁻¹ in two phosphorus-adequate soils. Phosphorus added to deficient and adequate soil significantly increased the cumulative CH₄ and N₂O emissions compared to the solely glucose added soil and the combination of glucose with phosphorus. Glucose addition significantly increased microbial biomass carbon (MBC) but decreased microbial biomass phosphorus (MBP), especially in the phosphorus-adequate soil. For MBC, the highest value obtained was 175.8 mg kg⁻¹, which was determined under glucose addition in phosphorus-adequate soil. The soil pH increased with glucose addition but decreased with phosphorus addition in phosphorus-deficient soil. The soil organic carbon (SOC) content was significantly affected by glucose addition in the phosphorus-deficient soil. Available phosphorus (AP) was highly influenced by phosphorus addition but did not appear to be affected by glucose addition. From the current study, we concluded that sole phosphorus and glucose addition increase CH₄ andN₂O emissions in phosphorus-deficient and also in phosphorus-adequate paddy soils. Further study will be conducted on sole and interactive effects of glucose and phosphorous on soil with plants and without plants.