Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
8487053 | Agriculture, Ecosystems & Environment | 2018 | 13 Pages |
Abstract
In rice production, water-saving irrigation management is expanding and likely alters depth profiles of soil moisture, redox potential (Eh) and microbial activity. It is, however, unclear how such conditions then impact net soil N-release and availability to the rice crop, because we do not know well enough how water-saving irrigation management shapes depth-distribution of Eh and reductive processes, and microbial activity. A field experiment with rice was laid out on a typical young floodplain paddy soil of Bangladesh with three irrigation schemes, viz. continuous flooding (CF), safe alternate wetting and drying (AWD) and direct seeded rice (DSR), with 120â¯kgâ¯Nâ¯haâ1 (N120) or without (N0) urea application. We evaluated changes in soil mineral N and plant N uptake, CH4 and CO2 emissions and soil pH, and at multiple depths soil Eh and temperature, dissolved C, Fe and Mn throughout 2015 dry (Boro) season (Jan-Apr). Eh stayed at or above â¼+300â¯mV except for sudden drops to â¼â200â¯mV with irrigation events in DSR. Eh quickly dropped to methanogenic conditions, under both AWD and CF; rises to â¼+200â¯mV were observed during AWD-drainage events but were restricted to upper 5.5 or 12.5â¯cm depths. Throughout the growing season there was a pronounced increase in reductive dissolution of Fe and Mn (hydro-) oxides, buildup of dissolved C, and CH4 effluxes under AWD and CF but not DSR, likely at least partially driven by the gradual soil warming from â¼20â¯Â°C till 28â¯Â°C. Predominant aerobic conditions under DSR lead to a nearly doubled C-emissions (CO2â¯+â¯CH4) compared to AWD and CF, suggesting more soil organic matter (OM) degradation in the former case, while soil mineral N plus plant N build-up rate followed an opposite order. Urea application did not raise soil exchangeable N levels, even prior to significant plant uptake from 28 DAT (days after transplanting), and we forward temporal abiotic NH4+-fixation and N-removal processes as explanations. We conclude that regardless of some distinctions in temporal evolutions of puddle layer Eh, solution C, Fe and Mn, and CH4-emission, soil N-supply was quite comparable under AWD and CF, as was rice yield. In the context of N availability, AWD could be safely adopted for rice growth in the Bangladeshi Boro season. The eventual fertilizer N recovery efficiency was higher for CF (42%) than for AWD (32%), but AWD saved 12% irrigation water. While DSR saved 45% water there was a large yield penalty, likely due to drought stress but also by poor germination caused by cold night temperatures in mid-January, while seedling transplantation in CF and AWD plots was only later on 28 January. Further research should be conducted to investigate the fast and pronounced removal of exchangeable inorganic N after initial N buildup by soil OM mineralization, especially in CF and AWD. At this moment most likely candidate processes appear clay-NH4+ fixation and anaerobic NH4+-oxidation.
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Authors
Masuda Akter, Heleen Deroo, Ahammad Mostafa Kamal, Mohammed Abdul Kader, Elizabeth Verhoeven, Charlotte Decock, Pascal Boeckx, Steven Sleutel,