Siyuan Cui

In China’s subtropical rice–wheat cropping system, the changes in the soil organic carbon (SOC) pool due to long-term straw return and its connection with crop yield remain unclear. This study aims to provide insights into establishing a sensible straw return system by evaluating the differences in the distribution and variation rates of SOC, light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), particulate organic carbon (POC), and mineral-associated organic carbon (MOC) in the 0–20 cm soil layer under different durations of straw return. Additionally, the study analyzes the relationship between the changes in SOC and its fractions and wheat yield. The experiment was conducted in 2019 in a rice–wheat rotation field with ten years of straw return treatments: no straw return (NR) or 1, 2, 3, 4, 5, 6, 7, 8, 9 year(s) of straw return (SR1–9), and an additional treatment in 2020 (10 years of straw return, SR10). The results revealed that with an increase in the duration of straw return, the contents of SOC, LFOC, HFOC, and POC gradually increased, showing the highest increments of 45.88%, 187.22%, 41.55%, 97.89%, and 28.21%, respectively, compared to the NR treatment. However, after eight years of straw return, the compound annual increase in soil organic carbon and its components was lower than in years 1–8, indicating a trend of diminishing increments. The SOC content and its variation were significantly correlated with the content and variation of LFOC, HFOC, POC, and MOC, with the highest sensitivity observed for the variation in LFOC, indicating the strong influence of the duration of straw return. The SOC and its fraction contents showed significant positive correlations with wheat yield, with the highest contribution to wheat yield increase attributed to an increase in LFOC content. In summary, straw return enhances the 0–20 cm deep soil carbon pool, with LFOC being the most sensitive indicator, reflecting the influence of the duration of straw return on soil carbon pools.

Straw return is an important farmland management practice that influences the activity of soil nitrogen. Few studies have examined the distribution of soil nitrogen and its components in wheat–rice cropping fields in subtropical China. This study assesses the influence of different years of straw return on the distribution and variation of total soil nitrogen (TN), light fraction nitrogen (LFN), heavy fraction nitrogen (HFN), particulate nitrogen (PN), and mineral-bound nitrogen (MN). We conducted a field experiment with eight years of straw retention treatments in 2017 (no straw retention, NR; 1 year of straw retention, SR1; 2 years of straw retention, SR2; 3 years of straw retention, SR3; 4 years of straw retention, SR4; 5 years of straw retention, SR5; 6 years of straw retention, SR6; 7 years of straw retention, SR7) and one more treatment in 2018 (8 years of straw retention, SR8) in a rice–wheat cropping system at Yangzhou University Experimental Station in China. The results demonstrated that as the number of years of treatment increases, the content of TN, LFN, HFN, PN, and MN at each soil layer gradually increases. Compared with NR, the highest increase in TN, LFN, HFN, PN, and MN under SR1-SR8 in the 0–20 cm soils was 38.10%, 150.73%, 35.61%, 79.97%, and 27.71%, respectively, but increases in TN, HFN, and MN content gradually slowed after six years of straw return. The contents or variation of TN were extremely significantly correlated (p < 0.01) with that of LFN, HFN, PN, and MN, while LFN had the highest variation. In general, straw return could improve the quality of the 0–20 cm nitrogen pool. LFN was the best indicator of changes to the soil nitrogen pool affected by years of straw return.

It is of great significance to explore the effects of different tillage practices on total nitrogen and its components in rice-wheat rotation farmland. The experiment was carried out in Jiangyan County, Jiangsu Province of China, and a total of four treatments were set up: minimum tillage (MT), rotary tillage (RT), conventional tillage (CT), and conventional tillage without straw retention (CT0). The total nitrogen (TN), light fraction nitrogen (LFN), heavy fraction nitrogen (HFN), particulate nitrogen (PN), and mineral-associated nitrogen (MN) in 0-20 cm soil were determined. The results show that MT increased TN concentration by2.26%-27.57% compared with the other treatments in 0-5 cm soil, but it lost this advantage in 5-10 cm and 10-20 cm soil. MT altered the concentration of LFN by 6.03%-95.86%, of HFN by 1.68%-20.75%, of PN by 12.58%-96.83%, and of MN by −1.73%-9.83% as compared to RT, CT, and CT0 in 0-5 cm soil, respectively. With the deepened of soil depth, the concentration of TN, LFN, HFN, PN, and MN decreased quickly in MT, which was lower than that in RT and CT at 10-20 cm soil depth. Straw return increased the concentration of TN and its components in 0-20 cm soil. The concentration of TN was extremely significantly positively correlated with that of LFN, HFN, PN, and MN (p<0.01). The variation of TN was significantly positively correlated with that of LFN, HFN, PN, and MN (p<0.01), and LFN showed the highest sensitivity to tillage practice. In general, minimum tillage combined with straw retention increased the concentration of soil TN and its components in topsoil. LFN was the best indicator to indicate the change in soil total nitrogen affected by tillage practice. Keywords: rice-wheat rotation, soil active nitrogen components, light fraction nitrogen, heavy fraction nitrogen, particulate nitrogen, mineral-associated nitrogen DOI: 10.25165/j.ijabe.20221503.5661 Citation: Cui S Y, Zhu X K, Cao G Q. Effects of tillage on soil nitrogen and its components from rice-wheat fields in subtropical regions of China. Int J Agric & Biol Eng, 2022; 15(3): 146–152.

Crop straw is an important natural resource in China because it is rich in nutrients. When returned to fields after harvests, the straw can improve soil quality and the next crop’s yield. Evaluating the economic values of the main ecological services of a farmland ecosystem while implementing the straw return technique can be a more systematic and comprehensive approach to better understand the contribution of straw return to the development of ecological agriculture. Based on the data of a field experiment established in 2010 with varying numbers of years of straw return, four ecological services, i.e., agricultural product and industrial raw materials, atmospheric regulation and purification, soil nutrient accumulation, and water conservation, were selected to estimate a net ecosystem service value (ESV) of a wheat field’s ecosystem services. Agro-ecosystem service appraisal theories were applied to estimate the economic value of each service. Results showed that straw returning improved the total ESV in the wheat system. Compared to the no straw return treatment, 1 year, 3 years, 5 years or 7 years of straw returning altered the economic value of the agricultural product and industrial raw materials (EVAIM) by –5.93% to 7.84% and improved atmospheric regulation (EVAR) by 13.66%-30.80%, soil nutrient accumulation (EVSNA) by 59.87%-233.31% and water conservation (EVWC) by 2.60%-13.26%. The total ESV of wheat plots with 1-7 years of straw returning was 3.67%-27.41% higher than that with no straw return, and the total ESV increased with the increase in years of straw return. The proportion of EVAIM out of the total ESV in this wheat field system was highest (accounted for 47.09%-55.64%), followed by EVAR and EVWC. The value of EVSNA was the lowest. However, the proportion of EVSNA was higher than that of water conservation after the fifth year of straw return. In general, the adoption of continuous straw returning in a wheat field ecosystem is ecologically valuable. The results can inform the development and implementation of ecological compensation policies involving straw return. Keywords: ecosystem service value, rice-wheat rotation, straw returning, farmland ecosystem, economic value, ecological service function DOI: 10.25165/j.ijabe.20211401.5698 Citation: Cui S Y, Cao G Q, Zhu X K. Evaluation of the ecosystem service of straw return to soil in a wheat field of China. Int J Agric & Biol Eng, 2021; 14(1): 192–198.

Tillage practices affect the fate of N fertilizer by influencing its transformation. Few studies have examined N leaching and N₂O emission from double‐cropped paddy fields in southern China. This study was aimed at assessing the influence of tillage systems on saturated hydraulic conductivity (K_s), N leaching, and N₂O emission from double‐cropped paddy fields in southern China. The experiment was conducted with rice (Oryza sativa L.) during the growing seasons of 2010 and 2011. Four treatments in a randomized complete block design were: no‐till (NT), conventional tillage (CT), rotary tillage (RT), and conventional tillage with residue removed (CT0). Results showed that NT significantly increased K_s at the 0‐ to 40‐cm depth relative to other treatments (P < 0.05); however, there were no significant differences in K_s at the 40‐ to 80‐cm depth. Compared with other treatments, the mean K_s for NT at the 0‐ to 80‐cm depth increased significantly (P < 0.05), by 76.3, 44.7, and 64.8% compared with CT, RT, and CT0, respectively. Despite significant differences (P < 0.05) on some occasions, higher concentrations of NH₄⁺–N and NO₃^––N were observed in soil solutions from NT than from other tillage treatments. Conversion of CT to NT reduced N₂O emissions, and the magnitude of reduction was usually significant (P < 0.05) compared with other treatments, especially during the stage of peak emissions. Therefore, in the context of yield increase, environmental concern, and climate change, integrated N management under a NT system in paddy fields is needed to attain high N use efficiency and crop yield.