Introducing conservation agriculture on irrigated Meadow alluvial soils (Arenosols) in Khorezm, Uzbekistan

Abstract

Uzbekistan's economy depends to a great extent on agriculture, particularly on revenues from irrigated cotton (Gossypium hirsutum L.) production. Since poor soil fertility and high soil salinity are the major obstacles in crop production, conservation agriculture (CA) may offer the potential to increase soil fertility and crop yields, reduce soil salinity and, thus, save water used for leaching salts out of the soil. Furthermore, compared to the wealth of data on CA in rain fed areas worldwide, scarce information exists on CA under irrigated conditions. This study aims at identifying the potential of reduced tillage (selected CA practices) on soil para-meters and crop yields under irrigated agriculture in a cotton-wheat rotation on salinity affected areas in Khorezm. A complete randomized field experiment with four replications was conducted 2002-2005 in Khiva, a district of the Khorezm province of Uzbekistan. For the first time in Khorezm, four tillage treatments were tested and compared: conventional tillage (CT; control), intermediate tillage (IT), permanent bed planting (PB), and zero tillage (ZT). Treatments were with and without retention of crop residues (+CR and -CR), and all were furrow irrigated except for ZT that was flood irrigated. The crucial soil parameters, i.e., soil organic matter (SOM), salinity, and total nitrogen (N) were monitored, together with crop yields. Data ana-lysis included statistical appraisals with ANOVA and multiple regression as well as mapping with ArcGIS. The results of the combined analyses show important tendencies such as an overall SOM increase with time and a reduced soil salinity increase under CA practices, and the yield-reducing effects of salinity. The ArcGIS maps reveal a certain variation in SOM over the entire experimental area, but all values remained within the moderate category, although wheat (Triticum aestivum L.) yields were reduced in the more saline areas of the large-scale experimental field. The ANOVA results show that CR retention had a slightly positive effect (yet not significant) on the SOM and N contents, and that it did not affect yields. CR retention slowed down the salinity increase over time. The SOM was significantly higher under ZT and PB, and soil salinity was significantly lower, but these differences remained below 13% compared to CT. Due to a high variability in yields, the effects on yields were insignificant, but cotton yields were very low under ZT and IT. Cotton yields were high under CT and PB (+CR), and high wheat yields were observed under PB. Wheat yields under IT were high, but in combination with the cotton yields, this system cannot be recommended. The PB practices are a good alternative to CT that may lead to yield declines in the long run due to the build-up of soil salinity. These first results from 3 years of cropping immediately after introducing CA practices hold sufficient promise for CA and residue retention (mulch) in irrigated drylands. But further studies are needed to understand long-term dynamics and to elaborate detailed land management procedures to increase the sustainability of dryland agriculture.