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
Recommended Citation
Fallah, Vali M., "Nitrogen supplying capacity of Iranian rice soils" (1995). Graduate Student's Output. 3355.
https://www.ukdr.uplb.edu.ph/etd-grad/3355
Notes
Doctor of Philosophy ( Soil Science)