Abstract

Man-induced soil changes have been named metapetiogenesis by the Israeli soil scientists Yaalon and Yaron. The present study deals with the effect of application of runoff water to fields surrounded by earth-walls, limans, and is thus a case of metapedogenesis. Runoff agriculture has a long tradition in the Negev desert, and reached its most sophisticated level with the Nabateans during the Byzantine period. It was later abandoned for many centuries, but was reintroduced by the end of the 1950s by Professor M. Evenari and his fellow researchers N. Tadmor and L. Shanan. They established Wadi Mashash experimental farm in 1971, and here the liman system of rainwater harvesting has developed. In the present study, 6 limans of different age were investigated: 72./1, 79/2, 83/2, 83/7, 86/3 and 93/4. Olives grow in the first three, acacia and eucalyptus in the next two, and Sudan grass in the last. I investigated soil pH, electrical conductivity (EC), organic carbon content and particle size distribution. Around 30 samples were taken from two depths, 0 - 20 cm and 20 - 40 cm, in each liman. The samples belonged to three locations: a) In rows (close to the trees, undisturbed land) b) Between rows (rotavated land) and c) Outside the liman (control). pH and EC was measured on all samples, while organic carbon and soil texture only in the upper layer. The natural pH is very high. In the upper layer, all mean values, except one, lay between 7.7 and 8. The exception was 72/1, in the rows, which had a pH value of 7.1. In the lower layer there was no real variation, with a range from 7.4 to 8.2, and no clear trend. The main process for lowering the pH is thought to be the breakdown of litter in the limans, accompanied by release of organic acids. The EC from control samples showed a very large variability, between 0.2 and 17 mS/cm. Inside the limans, the EC was without exception low, between 0.2 and 0.4 mS/cm. Liman 93/4 had only been flooded once, but showed comparable EC values to the others. The mean of all control samples for organic matter was as low as 0.35 %. To raise the organic matter content in a hot climate is difficult, but the interaction of trees and grass is probably beneficial. Alteration of aerobic and anaerobic conditions can be important. No trend was detectable, but the average value for all limans, excluding 93/4, is 0.6 %. Earthworms were found in the sample with the largest individual value (1.2 %). Particle size distribution is usually difficult to change, but in this case it is evident that eroded material has been transported into the limans. Liman 79/2, 83/7 and 86/3 showed a clear increase in the amount of clay and silt compared to their surrounding, while limans 72./1 and 83/2, which had the highest water income, showed none. Flooding of liman surroundings is maybe the cause. My calculations, based on data from the Sede Boker region, showed that the oldest liman could already have received about 4.5 cm of sediment, and would, at this rate, silt up in 150 years. All observed changes of the studied properties were positive, and this type of runoff farming is, from the soil point of view, either harmless or beneficial

Keywords

limans; earth-wall; Negev desert; agriculture; runoff farming

Published in

Avdelningsmeddelande / Sveriges lantbruksuniversitet, Institutionen för markvetenskap, Avdelningen för lantbrukets hydroteknik
1994, number: 94:2
Publisher: Institutionen för markvetenskap, avdelningen för lantbrukets hydroteknik, Sveriges lantbruksuniversitet

UKÄ Subject classification

Fish and Aquacultural Science
Agricultural Science

Permanent link to this page (URI)

https://res.slu.se/id/publ/30060