Table 1_Eco-optimizing rice-wheat system of Eastern Indo-Gangetic plains of India through resource conservation technologies: insights from field experiments and modeling.docx

In eastern India, the rice-wheat cropping system (RWCS) faces challenges like poverty, fragmented landholdings, and resource overexploitation, with smallholder farmers prioritizing short-term gains through excessive water and nitrogen use. To address these issues, our study combined field experiments and the DNDC crop simulation model to evaluate the resilience, viability, and environmental sustainability of RWCS under conservation agriculture (CA) with varying irrigation methods and nitrogen rates at the International Rice Research Institute-South Asia Regional Center (ISARC), Varanasi, India. The treatments included: (1) Puddled transplanted rice followed by zero-tilled wheat with flood irrigation (PTR-ZTW-F), (2) Direct-seeded rice followed by ZTW with flood irrigation (DSR-ZTW-F), (3) DSR followed by ZTW with surface drip fertigation (DSR-ZTW-SD), and (4) DSR followed by ZTW with subsurface drip fertigation (DSR-ZTW-SSD), evaluated under 75% and 100% recommended nitrogen dose and nitrogen control plots. The DNDC model accurately predicted soil mineral N (NO3−: R2 = 0.74, RRMSE = 52.9%; NH4+: R2 = 0.79, RRMSE = 63.5%), water-filled pore space (R2 = 0.85, RRMSE = 20.9%), soil temperature (R2 = 0.91, RRMSE = 4.6%), redox potential (R2 = 0.82, RRMSE = 24.1%), system productivity (R2 = 0.93, RRMSE = 7.8%), and nitrogen uptake (R2 = 0.86, RRMSE = 18.1%). DSR-ZTW systems with drip fertigation significantly enhanced sustainability and productivity compared to PTR-ZTW system, where CH4 emissions were reduced by 70%–80% and global warming potential reduced by 56%, despite higher N2O emissions. Additionally, DSR-ZTW-SSD achieved the highest system yield (12.8 t ha−1), minimized water losses, and improved nitrogen use efficiency. Also, TOPSIS analysis ranked DSR-ZTW-SSDF as the most sustainable system, achieving the highest yield and resource use efficiency, while significantly reducing GHG emissions. The study underscores the potential of integrating CA, drip fertigation, and DSR to enhance productivity, conserve resources, and improve the sustainability of RWCS.

印度东部的稻麦轮作系统（rice-wheat cropping system, RWCS）面临贫困、土地细碎化与资源过度开发等多重挑战，小农农户往往通过过量施用水肥以追求短期收益。为解决上述问题，本研究结合田间试验与DNDC作物模拟模型，在印度瓦拉纳西的国际水稻研究所南亚区域中心（International Rice Research Institute-South Asia Regional Center, ISARC），评估保护性耕作（conservation agriculture, CA）配施不同灌溉方式与氮肥用量时，稻麦轮作系统的抗逆性、生产可行性与环境可持续性。试验设置如下4个处理：(1) 水整地移栽稻+免耕小麦漫灌（PTR-ZTW-F）；(2) 直播稻+免耕小麦漫灌（DSR-ZTW-F）；(3) 直播稻+免耕小麦地表滴灌水肥一体化（DSR-ZTW-SD）；(4) 直播稻+免耕小麦地下滴灌水肥一体化（DSR-ZTW-SSD）。所有处理均设置75%推荐施氮量、100%推荐施氮量及无氮对照小区。DNDC模型可准确预测土壤矿质氮（硝态氮NO3−: 决定系数R2=0.74，相对根均方误差RRMSE=52.9%；铵态氮NH4+: R2=0.79，RRMSE=63.5%）、土壤孔隙充水率（R2=0.85，RRMSE=20.9%）、土壤温度（R2=0.91，RRMSE=4.6%）、氧化还原电位（R2=0.82，RRMSE=24.1%）、系统生产力（R2=0.93，RRMSE=7.8%）与氮素吸收量（R2=0.86，RRMSE=18.1%）。相较于水整地移栽稻-免耕小麦漫灌处理，采用滴灌水肥一体化的直播稻-免耕小麦系统可显著提升系统可持续性与生产力，尽管其N2O排放有所升高，但甲烷（CH4）减排幅度可达70%~80%，全球增温潜势降低56%。其中，地下滴灌水肥一体化处理（DSR-ZTW-SSD）的系统产量最高，达12.8 t ha−1，同时可最小化水分损失并提升氮肥利用效率。此外，通过逼近理想解排序法（TOPSIS）分析可知，DSR-ZTW-SSDF为最优可持续系统，可实现最高产量与资源利用效率，并显著降低温室气体排放。本研究证实，将保护性耕作、滴灌水肥一体化与水稻直播技术相结合，可有效提升稻麦轮作系统的生产力、资源保育能力与整体可持续性。