Nitrogen supplying capacity of Iranian rice soils

Date

6-1995

Abstract

Currently, nitrogen (N) fertilizer recommendation for rice production in Iran is based on mean N-response to N rates studied at several locations. This general recommendation does not account for variabilities in N-supplying capacity among locations.

This study was undertaken to provide information that reliably account for different N-supplying capacities of rice soils leading to s "judicious" fertilizer recommendation for higher rice yield, more efficient rice production and lower environmental pollution. Soils from 25 sites in the major rice growing area of Mazandaran, Northern Iran, were sampled for field characterization and study of N-release pattern under anaerobic incubation. Soil organic-N fractions were determined in these soils to investigate the contribution of each individual fraction to mineralized-N during anaerobic incubation. Based on soil characterization thirteen sites were selected for field experiments to evaluate relationship between soil-N supplying capacity and yield, yield response, as well as N-uptake of rice crop.

At seven of these sites additional field experiments were conducted to establish N-response curves of rice to increasing N-application rates and to develop recommendation for N-application rate.

Anaerobic incubation study at 35oC during 4 weeks revealed that N-release pattern showed an initial flush of released-N within one week followed by slow release rates. The high significant correlation obtained between N-released during one week anaerobic incubation and grain yield or plant N-uptake in field indicated the importance of the initial N-release and probable positive relationship between the initial and later N-supplying capacity. Fractionation of soil organic-N were performed by acid hydrolysis. Organic-N fractions showed significant correlation with mineralizable-N and the order of correlation coefficients were as follows: nonhydrolysable-N = hydrolyzable ammonium-N > amino acid-N > amino sugar-N > unidentified-N. The ratio of polysaccharide-C to amino acid-N had higher correlation with mineralizable-N than the ratio of total-C to total-N, although correlation value for the former was still small and not reliable.

Field experiments at 13 sites with PK and NPK treatments indicated that total-N, organiz-C, N-released during one week incubation, acid dichromate-N and alkali permanganate extractable-N could significantly account for variation in yield, yield response and plant N-uptake. N-response curve study at 7 fields reliably validated the N-availability indices for adjusting N-rates application ensuring maximum yield production and lower environmental pollution. At location having very low N-supplying capacity (Nt% = 0.12, O.C% + 1.07), 92 kg.N.ha-1 was necessary to obtain 4.5 tons.ha-1 of grain yield of the test cultivar (Tarom), while 23 kg.N.ha-1 was sufficient to the same yield level at location having a high N-supplying capacity (Nt% = 0.28, 0.28, 0.C% = 2.11). The optimum soil C content above which yield response to applied N-rates decreased was 2.11%. Agronomic N-use efficiencies were the same across all N-responsive locations with relevant optimum rates of fertilizer application. Recovery efficiency from applied optimum N-rate was inversely related to the soil-N supplying capacity.

Document Type

Dissertation

Degree

Doctor of Philosophy in Soil Science

College

Graduate School (GS)

Adviser/Committee Chair

Henry P. Samonte

Co-adviser

Heinz-Ulrich Neue

Committee Member

Restituta P. Robles, Rodrigo B. Badayos, Mariano B. De Ramos

Language

English

LC Subject

Rice--Soils, Soils--Nitrogen content

Location

UPLB Main Library Special Collections Section (USCS)

Call Number

LG 996 1995 S72 F35

Notes

Doctor of Philosophy ( Soil Science)

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