Herbicides in tropical soils and water

In the U. K., the amount of herbicides used on about 4.15 million hectares of agricultural land in 1973 was considered enough to provide 30 ppm if mixed evenly into the top 0.5em of the treated area (Greaves et al., 1976). How soon quantities of this kind will be used in the topics is not known. It is the responsibility of agriculturalists to maintain the productivity of the soil, and one aspect of this task is to ensure that levels of herbicides in soils and water are kept _low

Changes in nutritional types in bacterial successions

In a succession in which three bacteria having different nutritional needs were inoculated simultaneously into a medium with no added growth factors, the fastidious population developed only after an initial period of growth by bacteria with simple nutritional demands. In a model succession of soil bacteria inoculated into a glucose–salts medium, the relative abundance of cells requiring no growth factors declined with time, while bacteria needing growth factors made up an increasing percentage of the community in late stages of the succession. </jats:p

Biological nitrogen fixation in farming systems of the tropics

This book is the proceedings of a symposium held at the International Institute of Tropical Agriculture, Ibadan, Nigeria in Oct. 1975. It is divided into sections on general considerations (3 papers); legumes in farming systems of the tropics (4 papers); ecology and physiology of rhizobia (6 papers); nitrogen fixation in legumes (7 papers); non-legume sources of biological N in nature (6 papers); and measuring N gains and losses in farming systems (4 papers). The following are noted

Decomposition of Carbon14 labelled ryegrass and maize under tropical conditions

This work is an extension of earlier studies on the rate of decay of plant material in the forest zone of Nigeria. Maize (Zea mays L.) leaves, uniformly labeled with 14C, were allowed to decompose for 2 yr under field conditions in an Alfisol (pH 7.0) or an Ultisol (pH 4.7). After two years, 15% of the original plant C still remained in the Alfisol. Decomposition was slower in the Ultisol, particularly during the first 26 wk. Maize leaves incorporated in soil at the beginning of the dry season initially decomposed more slowly than leaves incorporated during the wet season, but by the end of 2 yr the difference was small. Earlier experiments in Nigeria with labeled ryegrass (Lolium multiflorum Lam.) tops were continued: after 5 yr, 8% of the original ryegrass C remained in an Alfisol. After adjustment for differences in climate and soil texture, the current Rothamsted model for turnover of organic C in soil gave a close fit to the Nigerian data

Increased incidence of Pythium stem rot in cowpea treated with benomyl and related fungicides

In six replicated field trials during a 3-year period the incidence of cowpea wet stem rot caused by Pythium aphanidermatum was significantly greater in plots treated with benzimidazole (BZ) fungicides than in plots treated with non-BZ fungicides and nontreated plots. In laboratory studies, the growth of P. aphanidermatum in corn-meal agar was unaffected by the addition of up to 250 µg/ml active ingredient of the BZ fungicides. It seems likely that the broad-spectrum, yet selective, BZ fungicides favor the activity of P. aphanidermatum by suppressing antagonists and competitors