Straw returning (R) combined with the application of a decomposition agent (RD) can increase crop yield and soil carbon (C) storage. However, the effect of RD on soil nitrous oxide (N2O) emissions in tropical areas remains poorly understood. In this study, an in situ experiment was performed under different water management strategies (long-term flooding or alternate wetting and drying) with the R and RD treatments to evaluate soil N2O emissions and rice yield. The SOC and TN contents were significantly lower under the RD treatment than under the R treatment. The R treatment significantly increased rice yield; however, the yield was further significantly increased under the RD treatment. The soil N2O emissions and yield-scaled N2O emissions were higher under the R treatment than under the no-straw-returning treatment. However, the RD treatment greatly reduced soil N2O emissions and yield-scaled N2O emissions under various water management strategies compared with those under the R treatment. Moreover, yield-scaled N2O emissions were lower in the RD treatment than in the control. The soil N2O emissions and yield-scaled N2O emissions were distinctly higher under alternate wetting and drying than under long-term flooding. Our results indicated that long-term flooding and straw returning with decomposition agents can effectively increase rice yield and reduce soil N2O emissions in tropical areas.

Nitrogen fertilizers have a significant impact on the growth of rice. The overuse and inappropriate application of nitrogen fertilizers have resulted in environmental pollution, in addition to subjecting both humans and livestock to negative health hazards. Finding a viable substitute for traditional nitrogen fertilizers is crucial and essential to help improve crop yield and minimize environmental damage. Nano-nitrogen fertilizers offer a possible alternative to traditional fertilizers due to a slow/controlled release of nitrogen. The present work aimed to study the effect of a slow-release urea nanofertilizer on soil ammonical (NH4-N) and nitrate-N (NO3-N) content, culturable soil microflora, and soil enzyme activities in three different soil samples procured from Ludhiana and Patiala districts through a soil column study. Seven treatments, including 0, 50 (75 kg/ha N), 75 (112.5 kg/ha N), and 100% (150 kg/ha N) of the recommended dose (RD) of conventional urea and nano-urea fertilizer were applied. The leachate samples collected from nano-urea treatment exhibited NH4-N for the first two weeks, followed by NO3-N appearance. The higher NH4-N and NO3-N contents in the leachate were recorded for light-textured soil as compared to medium- and heavy-textured soil samples. The soil microbial counts and enzyme activities were recorded to be maximum in light-textured soils. Therefore, this slow-release formulation could be more useful for light-textured soils to decrease applied N-fertilizer losses, as well as for improving the soil microbial viable cell counts and soil enzyme activities. The effect of urea nanofertilizer on the growth and yield of direct-seeded rice (Oryza sativa L.) was also evaluated under field conditions. Both studies were performed independently. Numerically, the highest shoot height, fresh and dry shoot weight, and significantly maximum total chlorophyll, carotenoid, and anthocyanins were recorded in the T2 (100% RDF through nano-urea) treatment. The yield-attributing traits, including the number of filled grains and thousand-grain weight, were also recorded to have increased in T2 treatment. A numerical increase in NPK for plant and grain of rice at 100% RDN through nano-urea was recorded. The soil application of the product exhibited no negative effect on the soil microbial viable cell count on different doses of nano-urea fertilizer. The soil nitrogen fixer viable counts were rather improved in nano-urea treatments. The results reflect that nano-urea fertilizer could be considered as a possible alternative to conventional fertilizer.

In continuously-flooded paddies, the small, fast-growing aquatic plant duckweed ( Lemna minor L.) considered to compete with rice for nitrogen, thereby having a negative impact on early rice growth. While duckweed overpopulation was known can be effectively overcome through field water management, the influence of such management on the N fate and its use efficiency in rice-duckweed systems is poorly documented. Accordingly, a three-year (2020-2022) field experiment was conducted to examine the combined impact on rice yield, as well as N loss and utilization, of two water management approaches (flood irrigation, FI vs . alternate wetting and drying irrigation, AWD), factorially combined with two rice production systems (rice-duckweed, +D, vs. duckweed-free rice, -D). In AWD+D fields, the density of duckweed generally remained below 250 g m( - 2) (about 85 % coverage), whereas in FI+D fields it reached 100 % coverage (300 g m - 2 ) within 5 days after transplanting, with individual duckweeds overlapping one another. Following AWD irrigation, duckweed performed as a nitrogen cache, akin to a split fertilizer application, with the first of several splits occurring at the rice crop's early tillering stage. Within the first 2 days of a specific wet -dry cycle, duckweed can store 0.5-1.5 g N m( - 2) , and then, within a further 3 days, release 0.3-1.0 g N m( - 2) . In contrast, in FI+D paddies, this caching function occurred once under midseason drainage, with further N being stored in the duckweeds during the remaining rice production season. As a result, at harvest the 0-0.10 m soil layer's N level increased significantly ( p <0.05) in both FI+D (8.5-16.8 %) and AWD+D (14.9-20.8 %) compared to FI-D and AWD-D, respectively. Due to the coverage and storage -release function of duckweed, apparent N loss decreased in rice-duckweed system by 1.4-12.5 % in the FI field and 22.1-31.3 % in the AWD field compared to their respective duckweed-free systems. In FI fields, except for a 10 % relative reduction in nitrogen recovery efficiency (NRE) in 2020, duckweed didn't significantly affect rice yield or NRE. The yield reduction (3.5-6.7 %) and the NRE increase (0.8-7.4 %) under AWD-D ( vs . FI-D) was, in the presence of duckweed, compensated for and overrun, resulting in a greater yield (5.3-6.7 %) and NRE (5.4-28.9 %) in the AWD+D vs. AWD-D field. When duckweed was present, AWD irrigation improved the by-path nitrogen cycling through duckweed, making the AWD+D system more beneficial for rice cultivation and the agroecosystem's environment health. The AWD+D system offers a promising measure for building an efficient and sustainable rice-duckweed agroecosystem.