ISHS Acta Horticulturae 255: III International Symposium on Soil Desinfestation
VIEWS ON SOIL SOLARIZATION : THE NIGERIAN SITUATION |
| Author: | R.O. Ogbuji |
| Abstract:
After studying recent publications by Professor Katan of the Hebrew University of Jerusalem, and after discussing with Professor Coosemans during a visit occasioned by the Linkage Programme between K.U.Leuven and the University of Nigeria, Nsukka, I had some impressions about soil solarization. One impression is that the critical factors in the efficacy of soil solarization are sufficient heat in the soil, that is, lethal soil temperature from sunlight and sufficient water in the soil. Threading cautiously in the area of soil specialists, I thought I could also add that a factor of soil texture (percentage sand, silt and clay) could play some role. If these are true, then soil solarization as a new concept in soil disinfestation is a functional system that merges some of the physical and cultural methods already being practised to control soil nematodes and some other soil pests. Such methods include application of heat in any form, clean fallow, flooding and the use of cover crops in the control of soil nematodes. In the early to mid 1950's, workers like Mai and Lautz (1953) Santmyer (1955) and Treffitt and Hurst (1953) had exposed nematodes to temperature range of 40–55°C (104–133°F) for a short time and killed most of them. Since most animal enzymes are inactivated after short exposure to temperatures near 50°C, death can probably be explained on this basis (Santmyer, 1955). Death of nematodes kept in clean fallow is probably due largely to starvation. However, it is probable that desiccation and heat are strong factors, especially in light sandy soils. Crittenden (1953) made extensive use of clean fallow for the control of rootknot. Flooding with water primarily decreases the oxygen tension of soil and may kill nematodes by suffocation (asphyxiation). In addition chemicals lethal to nematodes such as butyric acid, propionic acid and hydrogen sulphide often develop in flooded soils of low pH containing large amounts of rapidly decomposing organic matter. These fatty acids could also develop when certain cover crops are ploughed under and ferment. In addition there is increased activity of nematode trapping fungi, predaceous nematodes and internal parasites of nematodes. It is known that when piles of organic matter decompose, endogenous heat also develops (National Academy of Sciences, 1968). My thinking is that field soil to be solarized is first ploughed and harrowed before it is irrigated wet. I assume that irrigating wet simulates flooding. Unlike in soil fumigation practices, organic residues in field soil to be solarized may not be meticulously removed. The irrigated (wet) soil is tarped. Length of solarization period could take two, three or four weeks depending on soil depth | |
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