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University of Nairobi (1977)

The effect of some tillage methods and cropping sequence on rainfall conservation in a semi-arid area of Eastern Kenya

Marimi, AM

Titre : The effect of some tillage methods and cropping sequence on rainfall conservation in a semi-arid area of Eastern Kenya

Auteur : Marimi, AM

Université de soutenance : University of Nairobi

Grade : Master of Science in Agronomy 1977

Résumé partiel
To the east and south of the central highlands of Kenya lies an area whose agricultural production is based on a low and unreliable rainfall. There are two cropping seasons in a year of roughly equal duration. The rainfall duration of each season seldom exceeds two months and heavy rain usually occurs during the first month from the start of rains. This, combined with structurally weak and rapidly capping, sandy clay or sandy loam soils, results in the loss of considerable amounts of rainfall as runoff. With little or no rainfall occuring after two months from the onset of the rains, it means that crops of three to four months duration have to reach maturity mainly with moisture stored in the soil, Hence crop failures are quite frequent. In this research project, selected tillage practices and cropping sequences were investigated to determine their’effectiveness in conserving rainfall. The research project was carried out at Katumani Agricultural Research Station, Machakos, which is situated within the target area. Minimum, conventional, cloddy and tied-ridge tillage methods were tried. It was expected that the different methods would have different effects on the infiltration capacity of the soil and hence on the proportion of rain which would be lost as runoff and that which would infiltrate into the soil. The cropping sequences included maize/maize, beJ3,ns/maize and bare fallow/maize, and it was expected that the d fferent sequences would conserve varying amounts of residual moisture at the end of the first season. The residual moisture would be carried over to aug - ment of rainfall received during the second season, and so help to obtain a better crop yield. The project was carried out during the long (April) and the short (November) rainy seasons of 1976 and the long rains of 1977. The data presented show that with low rainfall similar to thereceived during the long and the short rains of 1976(200mm or less) the deeper layers of the soil profile under the different tillage methods remained dry throughout the rainy season, because only a few of the daily showers were large enough to wet the soil deeper than 15-20cm. However significantly higher moisture contents were obtained under tied-ridges as compared to the other tillage methods following a wet period in Field M, hence demonstrating the superiority of tied ridges in conserving rainfall. Crop establishment was satisfactory on the minimum and the conventionally tilled seedbeds but less so on the cloddy and the tied ridge seedbeds. Subsequent growth was satisfactory on minimum, conventional and the tied ridge seedbeds but, adversely affected on the cloddy seedbed.Since the rain stopped too early for maize to reach maturity

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