Ammonia fluxes and emission factors under an intensively managed wetland rice ecosystem

Pyrolysis temperature and time of rice husk biochar potentially control ammonia emissions and Chinese cabbage yield from urea-fertilized soils

Current agricultural practices are increasingly favoring the biochar application to sequester carbon, enhance crop growth, and mitigate various environmental pollutants resulting from nitrogen (N) loss. However, since biochar's characteristics can vary depending on pyrolysis conditions, it is essential to determine the optimal standard, as they can have different effects on soil health. In this study, we categorized rice husk biochars basis on their pH levels and investigated the role of each rice husk biochar in reducing ammonia (NH3) emissions and promoting the growth of Chinese cabbage in urea-fertilized fields. The findings of this study revealed that the variation in pyrolysis conditions of rice husk biochars and N rates affected both the NH3 emissions and crop growth. The neutral (pH 7.10) biochar exhibited effective NH3 volatilization reduction, attributed to its high surface area (6.49 m2 g-1), outperforming the acidic (pH 6.10) and basic (pH 11.01) biochars, particularly under high N rates (640 kg N ha-1). Chinese cabbage yield was highest, reaching 4.00 kg plant-1, with the basic biochar application with high N rates. Therefore, the neutral rice husk biochar effectively mitigate the NH3 emissions from urea-treated fields, while the agronomic performance of Chinese cabbage enhanced in all biochar amendments.

Co-application of biochar and compost with decreased N fertilizer reduced annual ammonia emissions in wetland rice

Ammonia (NH3) emission from rice fields is a dominant nitrogen (N) loss pathway causing negative impacts on farm profitability and the environment. Reducing N fertilizer application to compensate for N inputs in organic amendments was evaluated for effects on N loss via volatilization, rice yields and post-harvest soil properties in an annual irrigated rice (Boro) – pre-monsoon rice (Aus) – monsoon (Aman) rice sequence. That experiment was conducted using the integrated plant nutrition system (IPNS; nutrient contents in organic amendments were subtracted from the full recommended fertilizer dose i.e., RD of chemical fertilizers) where six treatments with four replications were applied in each season: (T1) no fertilizer (control), (T2) RD, (T3) poultry manure biochar (3 t ha−1; pyrolyzed at 450°C) + decreased dose of recommended fertilizer (DRD), (T4) rice husk ash (3 t ha−1) + DRD, (T5) compost (3 t ha−1) + DRD, and (T6) compost (1.5 t ha−1)+ biochar (1.5 t ha−1) + DRD. The N loss via volatilization varied twofold among seasons being 16% in irrigated rice and 29% in the pre-monsoon rice crop. In irrigated rice, T6 had significantly lower NH3 emissions than all other treatments, except the control while in pre-monsoon and monsoon seasons, T6 and T3 were alike. Pooling the three seasons together, biochar (T3) or biochar plus compost (T6) reduced NH3 loss via volatilization by 36-37% while compost alone (T5) reduced NH3 loss by 23% relative to RD. Biochar (T3) and biochar plus compost mixture (T6) reduced yield-scaled NH3 emissions by 40 and 47% relative to the RD of chemical fertilizer (T2). The organic amendments with IPNS reduced the quantity of N fertilizer application by 65, 7, 24, and 45% in T3, T4, T5, and T6 treatments, respectively, while rice yields and soil chemical properties in all seasons were similar to the RD. This study suggests that incorporation of biochar alone or co-applied with compost and decrease of N fertilizer on an IPNS basis in rice-based cropping systems can reduce N application rates and NH3 emissions without harming yield or soil quality.

Farmers' fertilizer use gaps relative to government recommendations in the saline coastal zone of the Ganges Delta

Overuse or underuse of nutrients relative to recommendations is a likely cause of crop yield gaps and an impediment to the achievement of food security. Government-endorsed recommendations are developed to deliver the best evidence-based advice on balanced fertilizer; however, deviations of farmers' nutrient use from the recommendations are rarely examined. This study chose the salt-affected coastal zone of the Ganges Delta, where low crop productivity and cropping intensity by smallholders limit their income, to determine current nutrient use gaps for the first time of three cropping patterns in two representative districts of Bangladesh. A total of 246 farms were surveyed from three farm sizes. Farmers' nutrient use gaps were compared with Fertilizer Recommendation Guides published in 2012 (FRG-2012) and 2018 (FRG-2018). Relative to FRG-2012 recommendations, farmers used 12%, 70%, and 11% overdoses of N, P, and K, respectively, under two fully rice-based cropping patterns, but the level of overdoses increased with farm size. Rates of K (14%), S (28%), and Zn use were below the FRG-2012 recommendations, especially for the smallest category of farms. However, the FRG-2018, increased recommended N (5%), K (62%), S (12%), and Zn rates but reduced P (25%) rates for fully rice-based cropping patterns. In contrast with rice, regardless of farm size, farmers applied overdose nutrients to watermelon but compensated with underdoses in the subsequent monsoon rice implying that farmers prioritized fertilizer expenditure on the most profitable crop. For the cropping pattern with watermelon, farmers could reduce the use of N (69%) and P (46%) and increase the use of K (48%), S (5%), and B. Reducing NPK use gaps can save treasury for both the farmers and the governments by 39.1 and 73.8 USD ha^-1, respectively, under fully rice-based cropping patterns. Finally, our findings suggest there is scope to promote crop yields and sustainable intensification through balanced fertilizer use in a vulnerable saline region.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13593-022-00797-1.

Integrated Nutrient Management Enhances Productivity and Nitrogen Use Efficiency of Crops in Acidic and Charland Soils

Integrated Plant Nutrient System (IPNS) is practiced worldwide to maintain soil quality. Two field experiments were conducted in 2019 and 2020 in acidic and charland soils to assess the impact of different manures, viz., poultry manure (PM), vermicompost (VC), compost (OF), rice husk biochar (RHB), poultry manure biochar (PMB)-based IPNS, and dolomite over control on productivity and nitrogen use efficiency (NUE) of the Mustard-Boro-Transplanted Aman and Maize-Jute-Transplanted Aman cropping patterns, and on soil properties. The experiments were laid out in a randomized complete block design with four replications. The results showed that IPNS treatments significantly improved soil aggregate properties and total nitrogen in acidic soil, and bulk density in charland soil. In both years, IPNS treatments increased system productivity from 55.4 to 82.8% in acidic soil and from 43.3 to 115.4% in charland soil over that of control. IPNS and dolomite treatments increased nitrogen uptake from 35.5 to 105.7% over that of control and NUE in both soils in 2019 and 2020. PMB- and OF-based INPS treatments exhibited superior performances in both soils, and the impact was more prominent in 2020. Therefore, PMB- and OF-based IPNS can be recommended for maximizing system productivity and NUE with concurrent improvement of physicochemical properties of acidic and charland soils.