Effect of Chlorophyll Meter and Leaf Colour Chart Based Nitrogen Management on Grain N Uptake for Rice in Iran

Abstract

Over application of N in rice leads to low N recovery efficiency and

risk of NO₃ pollution of ground water. The chlorophyll meter also known

as SPAD meter, is a simple, portable diagnostic tool for identifying

crop N status. We used it to test need based N management approaches

for rice (Oryza sativa L.) in two varieties on a clay loam texture in

northern Iran. The overall objective is to develop optimal N-management

for Neda and Shirudi. Two varieties were grown under eight treatments.

Eight treatments included a zero-N control, chlorophyll meter 35, 37,

40, LCC 4 and 5. SPAD readings were taken weekly on the topmost

fully expanded leaves. Grain yield, yield attributes, total N uptake and

fertilizer - N use efficiency were measured in both varieties. Both LCC

and SPAD can be used to improve N management for Neda and Shirudi,

but the optimal SPAD threshold for determining the timing of N-application

was 35 and 37 for Neda and Shirudi, respectively. LCC treatments

indicated that N-management based on LCC shade 5 helped avoid

over application of N to rice. Neda had higher grain yield than shirudi,

but the difference in maximum grain yield among SPAD and LCC treatments

was insignificant. The two varieties didn't show a clear difference

in fertilizer-N use efficiency. It is suggested that when N-management

technology such as real time N-management (SPAD and LCC) were

used, would avoid to over application of N fertilizer by rice farmers.