Nitrogen fixation as influenced by pesticides and rice straw in paddy soils

Abstract

SummaryThe effect of three herbicides and an insecticide combination on nitrogen fixation in three paddy soils was investigated in a laboratory incubation study. The influence of pesticide combination on N2 fixation was evaluated in the presence and absence of rice straw under flooded and non-flooded conditions. In a non-flooded alluvial soil single or combined application of butachlor and carbofuran significantly stimulated N2 fixation. There was no effect on N2 fixation when thiobencarb was applied alone; but with thiobencarb in combination with carbofuran higher N2 fixation occurred. Both oxadiazone and thiobencarb had no effect on N2 fixation under flooded conditions, but in combination with carbofuran the N2 fixation was high. In acid sulphate saline Pokkali soil, rice straw application stimulated N2 fixation; the stimulatory effect of carbofuran either alone or in combination became more pronounced under flooded conditions. N2 fixation was low in a laterite Sukinda soil and the effect of pesticides was not changed by rice straw amendment. A uniform stimulation of N2 fixation occurred in soils when carbofuran was applied either singly or in combination with other herbicides tested. Results indicate that the effect of pesticides on N2 fixation varied with the rice straw application and water regime.

Alachlor and Metribuzin Herbicide on N2-fixing Bacteria in a Sandy Loam soil

“…But it was observed that lower number of bacteria was present in metribuzin treatment as compared to alachlor and its combined application. This finding indicated that Metribuzin induced the efficiency of the bacteria rather than their growth and multiplication (Jena and Rao, 1987;Debnath et al, 2002). Among the herbicides, metribuzin exerted highest stimulation as compared to untreated control soil also.…”

“…After incubating the agar plates at 25±1 °C for 7 days, cfu of the microorganisms grown on the respective agar plates were counted. Non-symbiotic N 2 -fixing capacities of the soil samples were determined by incubating 1 g soil from each sample in 50 ml Jensen's broth (Jena, 1987) containing 2% sucrose in conical flasks at 27±1 °C for 15 days Then total nitrogen was estimated by the method of Bremner 1996 in the broth. To estimate the changes of total N in soil samples, soil were analyzed following the method and soluble NO 3 − were measured in 2N KCl extract through distillation technique as described by Mulvaney (1996).…”

Effect of pendimethalin and quizalofop on N2-fixing bacteria in relation to availability of nitrogen in a Typic Haplustept soil of West Bengal, India

“…This was also in accordance with the findings of Das and Debnath (2006) who demonstrated that application of herbicides highly stimulated the fixation of atmospheric nitrogen in soil. The higher N 2 -fixation under pendimethalin from 30th to 60th day of sampling, despite lower number of bacteria as compared to quizalofop and its combined application indicated that pendimethalin induced the efficiency of the bacteria rather than their growth and multiplication (Jena and Rao 1987;Debnath et al 2002). Incidentally, there was a significant positive correlation (r = 0.819; Table 5) between the population of non-symbiotic N 2 -fixing bacteria and their activities in soil.…”