Nitrogen management through soil and plant analysis development and leaf colour charts in different groups of rice (Oryza sativa) varieties grown on Vertisols of Deccan plateau

Abstract

A field experiment was conducted during the rainy (kharif) and winter (rabi) seasons of 1997 98 at Rajendranagar, Hyderabad, to compare the N use efficiency of SPAD 502 (soil and plant analysis development) chlorophyll meter based N fertilizer management with recommended fixed schedule of N fertilizer . splits applied at critical growth stages and to assess the relation of SPAD and leaf colour chart (LCC) readings recorded at critical crop growth stages with grain of rice (Oryza sativa L.). In SPAD based N management, the N was applied when SPAD value decreased below 35 of fixed value and the amount applied as per the stage of the crop. Hybrids recorded higher grain yield of 4.85 and 5.16 tonnesfha during rainy and winter season respectively than scented and high yielding varieties respectively. The SPAD N application gave significantly higher grain yield than 135 kg Nfha during rainy season, while on par with that in winter. The agronomic efficiency (A kg grainfA kg N) and partial factor productivity (kg graintunit N) was higher for SPAD based N application than 135 and 90 kg Nka. The SPAD and leaf colour chart values recorded at critical stages were significantly higher with application of N. These values showed positive correlation (0.78 to 0.85 in rainy season and 0.78 to 0.90 in winter season) in both seasons at all crop growth stages, indicating use of LCC as a tool for N top dressing. Thus increased N fertilizer efficiency at high yield levels is possible in hybrids and high yielding varieties using a chlorophyll meter and LCC to monitor leaf N status and guide fertilize N timing in irrigated rice. These methods not only reduced N requirement but also improved congruence of N supply and crop demand than fixed timing of N application treatment.