nan Varinderpal-Singh

Need based nitrogen management using the chlorophyll meter and leaf colour chart in rice and wheat in South Asia: a review

Fertilizer nitrogen (N) is one of the major inputs in rice–wheat production systems in South Asia. As fertilizer N has generally been managed following blanket recommendations consisting of two or three split applications of preset rates of the total amount of N, improvement in N use efficiency could not be achieved beyond a limit. Feeding crop N needs is the most appropriate fertilizer N management strategy to further improve N use efficiency. Since plant growth reflects the total N supply from all sources, plant N status at any given time should be a better indicator of the N availability. The chlorophyll meter and leaf colour chart have emerged as diagnostic tools which can indirectly estimate crop N status of the growing crops and help define time and quantity of in-season fertilizer N top dressings in rice and wheat. Supplemental fertilizer N applications are thus synchronized with the N needs of crop. The chlorophyll meter may not be owned by South Asian farmers individually, but it can be made available to farmers through village cooperatives, extension specialists, and crop consultants. Leaf colour chart, a simple and cost-effective device has already penetrated into South Asian farming and increasing numbers of farmers are finding it helpful in efficiently managing N fertilizers. This paper reviews the results of investigations carried out using these diagnostic tools in managing need based N applications in rice and wheat in South Asia.

Performance of site-specific nitrogen management for irrigated transplanted rice in northwestern India

Abstract Leaf colour chart (LCC) guides fertilizer nitrogen (N) application to rice as per requirement of the crop on the basis of a critical leaf colour. We evaluated need-based N management in on-farm experiments at 350 locations in the Indian Punjab during 2002 – 2005. Following LCC-based N management, from 9.4 – 54.2 kg N ha−1, with an average of about 25% less fertilizer N was used, without any reduction in yield as compared to the practice of farmers of applying blanket N at fixed time intervals. Application of fertilizer N when colour of the first fully expanded leaf was less than LCC shade 4, increased nitrogen use efficiency from 48 – 65 kg grain kg N−1. Nitrogen requirement of rice was site-specific both in terms of time and the amount of fertilizer N applied. In 36% of the experiments, a dose of fertilizer N was applied 55 days after transplanting (DAT) of rice. Also there were cases where only one top dressing of N was required. The study reveals that practice of applying N at fixed growth stages of rice may not be adequate and LCC-based N management can result in efficient utilisation of applied N by rice.

A framework for refining nitrogen management in dry direct-seeded rice using GreenSeeker optical sensor

Site-specific N management using GreenSeekerTM was evaluated in direct-seeded rice.Panicle initiation is the appropriate stage to make corrective N management.Two algorithms for N management based on GreenSeekerTM proposed in this study.The proposed algorithms could maintain high grain yield and high N-use efficiency. To reduce the amount of wasted reactive nitrogen (N) reaching the environment and to achieve high N fertilizer use efficiency, a site-specific N management strategy using GreenSeeker� optical sensor (GS) was evaluated in dry direct-seeded rice (DDSR) in the north-western India. Four field experiments were conducted during 2011-2013 to develop an optical sensor algorithm for fine tuning in-season N fertilizer applications. It was demonstrated that panicle initiation of rice is the appropriate stage for applying GS guided N fertilizer dose. Application of a prescriptive dose of 60kgNha-1 in two or 90kgNha-1 in two or three equal split doses, followed by a corrective N dose guided by GS at panicle initiation stage resulted in rice yield levels comparable to that obtained by following general recommendation, but with lower total N fertilizer application. On an average, N use efficiency was improved by more than 12% when N fertilizer management was guided by GS as compared to when general N fertilizer recommendation was followed. The results prove the inadequacy of general recommendations for N fertilizer management in DDSR and possibility of increasing N use efficiency along with high rice yield levels through site-specific N fertilizer management using GS.