Successful cooperation among smallholders requires a close match between their existing experience and financial capacity and the types of cooperation required by any joint activity. It is often built on previous cooperative experience. A commonsense observation, but one frequently overlooked by many donors in practice, is that the demands one places on farmer groups should not exceed their current group management skills. This paper highlights the characteristics of successful farmer cooperation as well as some of the common mistakes made in trying to promote farmer groups. The analysis indicates that though groups have a role to play, group approaches do not provide an easy institutional response to the new pressures facing smallholders in a liberalised economy. Nor should farmer cooperation be viewed as a panacea for the development of rural areas.

The decomposition of atrazine, Iinuron andpicloram when incubated with two soils at four levels of application was measured for periods of 3 or 4 months. The applicability of zero-order, half-order, first-order and Michaelis-Menten kinetics was considered. None of the equations described the breakdown rates adequately in spite of the apparent theoretical advantage for using an expression of the Michaelis-Menten type. I n each case the rate of decomposition increased as the initial herbicide concentration decreased.

By using gas chromatography with an alkali flame detector, 0-001 p.p.m. of atrazine, ametryne and terbutryne in water from two sources could be determined with recoveries close to 100 per cent. Ultraviolet spectrophotometry was adequate at the 0.01 p.p.m. level for all three compounds but was unreliable at lower levels. With cathode-ray polarography, 0.005 p.p.m. of terbutryne and ametryne and 0.01 p.p.m. of atrazine could be determined.

No abstract

A gas chromatographic method for the determination of triallate is described. Samples are coldextracted with a mixture of 2,2,4-trimethylpentane and isopropyl alcohol, after which the extract is shaken with water and the aqueous phase discarded. With soil extracts, aliquots of the 2,2,4-trimethyl-pentane layer are injected directly, but straw and grain extracts require further cleanup with Nuchar Attaclay. Recoveries at the 0.1to i.O-p.p.m. level are in excess of 90% with soil and barley grain and 80% with barley straw. The method is sensitive to 0.05 p.p.m.