Nitrogen Mineralization and Availability at Critical Stages of Rice (Oryza sativa) Crop, and Its Relation to Soil Biological Activity and Crop Productivity Under Major Nutrient Management Systems

Abstract

Adequate nitrogen availability to plants for growth is one of the most important reasons for fertilizer application. Though organic alternatives are recommended, there is uncertainty of their nutrient release characteristics, especially during critical growth stages of a crop. In a 10-year-long experiment on nutrient management for rice-wheat cropping, ion exchange resin (IER) membrane strips were used as plant root simulators to determine daily NH 4 +-N and NO 3 −-N availability in soil solution during the rice growing season. The management included inorganic fertilizers at 100% recommended rate (F), compared to reduced rate (55%) of inorganic fertilizers supplemented with organic inputs via green manuring with Sesbania (GM), biomass incorporation of an opportunity legume crop-green gram (Vigna radiata) (LE), 1/3rd wheat stubble retention and soil incorporation (WS), 1/3rd rice stubble retention and soil incorporation (RS), and farmyard manure application (FYM). The total amount of available N (NH 4 + + NO 3 −) recorded for the full season was in the order GM (221 μg cm −2) > F (184 μg cm −2) > RS (181 μg cm −2) > FYM (176 μg cm −2) > WS (176 μg cm −2) > LE (175 μg cm −2). Both grain and straw yield related directly and significantly to the N mineralization in soil at 30-60 days after transplanting (DAT), indicating that fertilizer N application before 30 DAT and after 60 DAT could mostly be a loss in transplanted rice crop. Green manured (GM) soils maintained steadily high N mineralization rates throughout the rice growing period. The best alternative to cut down inorganic fertilizer use in rice cropping would be the biomass incorporation from leguminous green manuring crops. Integration of organics afforded almost 50% reduction in recommended inorganic fertilizer use while maintaining better N mineralization status at the critical growth stages of rice.

Nitrogen Availability and Use Efficiency in Wheat Crop as Influenced by the Organic-Input Quality Under Major Integrated Nutrient Management Systems

“…flooded conditions as prevailed in the case of rice in the preceding season (Bhardwaj et al, 2020). The characteristics of the organic amendment also played a role as evident from the case of FYM and cereal crop residue (WS, RS) based management.…”

“…The N availability scenarios in wheat crop were best represented by the combined effects of inorganic fertilizer application as well as residual N from organic amendments added in the rice season ( Bhardwaj et al, 2020 ). Only combined effects could explain well the availability scenarios ( Figure 4 ).…”

“…In the case of wheat crop with relatively drier/near-field-capacity soil condition, F management matched legume-based (GM, LE) and manure-based (FYM) managements in terms of N availability. This meant that in the case of legumes (GM, LE) and farmyard manure (FYM), 50% cut down of inorganic fertilizer is compensated by the residual N from the organic amendment application in the preceding rice season, and secondly, the inorganic fertilizer losses were lower under drier conditions and therefore effects of inorganic fertilizer lasted longer than under flooded conditions as prevailed in the case of rice in the preceding season ( Bhardwaj et al, 2020 ).…”

“…Since the nutrient availability is driven by water, organic sources with the quick release of nutrients (at each rain/irrigation event) would show better availability to plants. Residue from legumes (green manure crop Sesbania and opportunity legumecrop Vigna ) has considerably higher contents of N as well as narrower C/N ratio, thus leading to considerably more and quick release of N into soil solution for plant uptake ( Schomberg et al, 1994 ; Bhardwaj et al, 2020 ). The effects have been found to persist for longer periods, even years, with annual release as much as 5–10% per year, providing benefits to subsequent crops ( Fillery, 2001 ; Peoples et al, 2009 ; Khakbazan et al, 2014 ; St. Luce et al, 2015 ).…”

“…Nitrogen mineralization in aerated soils is noticeably different from submerged soils. In flooded and anaerobic conditions, a higher concentration of total organic nitrogen results in higher N mineralization ( Bronson et al, 2001 ; Bhardwaj et al, 2020 ). However, under aerobic conditions, soil water fluctuations, as in wheat cropping season, usually result in a greater production of NO 3 – -N ( Nunan et al, 2000 ).…”