|Evett, Steven - Steve|
Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2011
Publication Date: 4/21/2011
Citation: Ibragimov, N., Evett, S.R., Esenbekov, Y., Khasanova, F., Karabaev, I., Mirzaev, L., Lamers, J. 2011. Permanent beds vs. conventional tillage in irrigated arid Central Asia. Agronomy Journal. 103(4):1002-1011. Interpretive Summary: In rainfed or dryland crop production, limiting or omitting soil tillage and retaining crop residues (stalks, stems, leaves) on the soil surface can have positive effects, including less evaporative loss of water, better infiltration of rain water and snow melt, and greater yields with less money spent on fuel and on repairs of tractors and implements. However, such conservation agriculture practices have had mixed success in irrigated agriculture. A two year study of an irrigated winter wheat/grain corn rotation followed by two years of cotton was done using conventional tillage compared with a reduced tillage system involving permanent beds. To study the effect of residue amount, both tillage systems had either 25% or 100% of the crop residues retained on the surface after harvest. Greater residue retention resulted in smaller plant populations, which resulted in reduced yields. Permanent beds also resulted in smaller plant populations, which were related to compaction of the soil. Increases in soil organic matter resulting from greater residue retention and reduced tillage did not overcome these negative impacts. The relationship between plant population and yield was very strong, indicating that the main effect of limited tillage and residue retention was to reduce yield by limiting plant germination and seedling success. Alternative limited tillage systems should be investigated for irrigated production, including some version of strip tillage that clears residue from a strip of soil where seeds will be planted, thus allowing the soil to dry and warm enough for better success in establishing a larger plant population.
Technical Abstract: Conservation agriculture (CA) practices, including limited or no tillage and preservation of residues on the soil surface, have had mixed success in irrigated agricultural systems. The effects of tillage and crop residue management on soil properties and crop yields were studied in a two factorial split-plot experiment on a silt loam soil using a rotation of winter wheat (Triticum aestivum L, cv. Mars) and maize (Zea mays L., cv. Uzbekistan-306MV) for two years followed by cotton (Gossypium hirsutum L, cv. Bukhara-102) for two years. Two tillage methods (permanent beds, PB, with limited re-shaping and conventional tillage, CT) and two residue management practices (R25, 25% residue retention on a mass basis; and R100, 100% residue retention) were examined. Four years of PB+R100 resulted in marked differences in soil physical properties and soil organic carbon (SOC), relative to CT. Winter wheat grown in both CT and PB systems resulted in bulk density of topsoil (0-0.1 m) ranging from 1.31 Mg m 3 to 1.33 Mg m**-3, which is typical for this soil type. Results suggested, however, a greater likelihood of soil compaction and consolidation in the 0.2-0.3 m depth with the PB system regardless of residue management practices. Compared with the CT system and the PB+R25 treatment combination, the PB+R100 treatment combination increased the amount of water stable macroaggregates, however only in the fourth year. Cereal stubble made a greater contribution to SOC replenishment than did cotton residue. Also, the SOC increase rate in PB+R100 over four years was 0.70 Mg ha**-1 year while that for CT+R100 reached only 0.48 Mg ha**-1 in the 0-0.4-m depth. Poor early plant growth and reduced plant population in the PB system caused decreased irrigation water use efficiency (IWUE) and nitrogen use efficiency of maize and cotton grown consecutively in 2006 and 2007. The cotton IWUE in 2008 substantially improved in the PB+R100 treatment combination, increasing from 0.41 to 0.59 kg**-3. Different concomitant factors, such as smaller maize and cotton plant populations and cooler soil temperature at cotton emergence, decreased the crop productivity over the first three years. Despite the lower biomass production in the PB+R100 treatment combination, cotton crop productivity for the PB systems increased in 2008 compared with the previous cropping season.