The experiments consisted of four SPAD and LCC-N regimes, blanket N recommendation, green manure N regime and Controlled Release N (CRN) fertilizer regimes, which were compared with the zero-N regime. The technology involves the indirect measurement of leaf N status by the chlorophyll meter and LCC and N application only if the measured meter value is below the predetermined threshold value. The study reveals that N requirement with LCC was higher than SPAD for all the time intervals of measurements. In terms of NUE parameters, LCC was inferior to SPAD-N management, but the lesser cost of LCC, when compared to SPAD meter, provides an opportunity as a simple tool for the individual rice farmers to own it. The study also reveals that the application of controlled release N fertilizer as polymer coatings at the rate of 60% of blanket N recommendation would save 40% of fertilizer N.
Rice (Oryza sativa L.) is the staple food of more than half of the global population.
About 515 million tons of rice are produced each year in 89 nations of the world, and
the production will have to increase by 60 to 70% by the year 2025 to keep pace with
Asia's rising population (Hossain and Fisher, 1995) and it has to come from less land and
less inputs. Nitrogen (N) is the critical input that limits rice productivity, and increasing
the rice productivity would mean more supply of N to the crop. Farmers are generally
using greater than recommended rates of fertilizer N to maintain the yield levels (Pagiola,
1995). As a result, fertilizer N recovery efficiency, which is already not more than 50% (Katyalet al., 1985 and 1986) in the irrigated rice, has further declined because of irrational
N applications. Nitrogen applied in excess of the crop's demand is lost through
various pathways, which not only has a negative effect on the environment but also
reduces economic benefits to farmers.
The optimum use of N can be achieved by matching supply with crop demand.
In the past, the timing of fertilizer applications to match the demand with supply
was based on regional recommendations. Scientists have begun by developing a
simple `researcher' system for identifying crop N demand to examine the effectiveness of
the concept and then to modify and adapt the concept to develop a profitable
technology appropriate for small Asian farmers (Dobermann and White, 1999). A potential
solution has been tried to regulate the timing of N application in rice: use of a chlorophyll meter
(or SPAD meter) or Leaf Color Chart (LCC) based on actual plant needs
(Balasubramanian et al., 2003). The chlorophyll meter and LCC – most reliable and nondestructive
analysis methods – were used to determine the right time for N topdressing for rice (Bijay et al., 2002). The concept is based on the results that show a close link between leaf
chlorophyll content and leaf N content. Thus the chlorophyll meter or LCC can be used to quickly
and reliably assess the leaf N status of crops at different growth stages. The LCC, because of
its low cost for farmers, has shown much promise in the scattered studies conducted
in India and elsewhere. No attempt has been made to calibrate the time intervals for the
use of SPAD and LCC value for rice genotype, or to evaluate whether the SPAD or LCC
could be effective for applying N in rice. No comprehensive study has been made to measure
the performance of controlled release N fertilizer for rice. |
