Leaf colour chart: An incredible tool for field-specific management of fertilizer nitrogen in cereals in South Asia

Abstract

Leaf colour chart (LCC) as a tool for field-specific management of fertilizer nitrogen (N) in rice was introduced on a commercial scale in the last decade of 20th century. During last two decades, its use has also been extended to wheat and maize. Many studies have been carried out on LCC-based N management in South Asian countries where farmers apply substantial amount of fertilizer N to cereal crops, but do not strictly follow even the regional blanket fertilizer N recommendations. LCC-based fertilizer N management in cereals leads to improvement in N use efficiency over that observed with blanket recommendation. It is an attempt to review the development of LCCs in South Asia, the modes in which LCC can be used - adjustable time and N dose in real time, fixed time adjustable N dose, and fixed N dose adjustable time, and the results of studies on field-specific LCC-based fertilizer N management carried out on rice, wheat, and maize in different parts of South Asia. By applying fertilizer N as guided by LCC, improvement in N use efficiency is observed either through reduced total amount of applied N, increased yield, or both. Performance of LCC-based site-specific N management at on-farm locations has also been reviewed. Studies providing direct evidence of reduced losses of N to environment due to LCC guided fertilizer N management rather than regional blanket recommendations suggest that LCC is going to be an incredible tool to enhance food security and minimize N related environmental degradation in South Asia.