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Rheinischen Friedrich-Wilhelms-Universität Bonn (2008)

Potential of Conservation Agriculture for Irrigated Cotton and Winter Wheat Production in Khorezm, Aral Sea Basin

Tursunov Mehriddin

Titre : Potential of Conservation Agriculture for Irrigated Cotton and Winter Wheat Production in Khorezm, Aral Sea Basin

Auteur : Tursunov Mehriddin

Université de soutenance : Rheinischen Friedrich-Wilhelms-Universität Bonn

Grade : Doktor der Agrarwissenschaften (Dr. agr.) 2008

Intensive tillage of soils leads to their slow but steady degradation. Therefore, scientists and farmers have been turning their attention to a more sustainable development in agriculture based on reduced tillage. Zero and minimum tillage have found widespread application under rainfed conditions. However, there is paucity of information on such conservation tillage systems in irrigated agriculture. In Central Asia, little experience exists with reduced tillage under irrigation. The objectives of this study were, in the irrigated land of Khorezm, Uzbekistan (1) to compare the effects of three tillage practices on crop development and yield, i.e., zero tillage (ZT), permanent beds (PB) and an intermediate technology (IT) vs. the conventional tillage (CT), with (+CR) and without (-CR) crop residue retention ; (2) the development of a suitable seeder for local conditions in Central Asia ; and (3) a financial analysis of the tillage systems studied. During three years in a cotton / winter wheat / cotton rotation (complete randomized design, four replications), data on plant development throughout their vegetative phase and on crop yields were assessed. In the plant establishment phase, with CR, in 2004, the cotton was on average significantly higher under CT (7 cm), as compared to the ZT (5 cm). Without CR, the effects of tillage systems were insignificant. In 2006, cotton was higher under CT than ZT, in both, with (13 cm vs. 10 cm) and without CR (13 cm vs. 11cm, respectively). Cotton raw yield with CR was either significantly higher under conventional tillage (3422 kg ha-1 vs. 1790 kg ha-1, 2004) or not affected by the treatments (average 3288 kg ha-1, 2006). With CR, winter wheat yield under PB (6053 kg ha-1, 2005) was significantly higher than CT (4278 kg ha-1). Without CR, no tillage effects were observed for both crops. The effect of crop residues on cotton growth for both cotton seasons, 2004 and 2006, were insignificant. Raw cotton yield in the third year after winter wheat on the plots was significantly higher where wheat residues were retained (3525 kg ha-1 vs. 2844 kg ha-1). Neither winter wheat growth nor yield was affected significantly by the crop residues. Evaluation of a seeder imported from India showed that it had serious limitations. Its low clearance did not allow sowing cereals into the standing cotton and the seeder was only suitable for sowing de-linted cotton seeds. Therefore, a more universal seeder was newly developed and tested. This seeder is able to sow both cotton and wheat, has a high clearance, is capable of working with both linted and de-linted cotton seeds, and has two boxes, one for seeds, the other for fertilizers, which allows concurrent sowing and fertilization, thus saving fuel costs and labor. Summing these results up, in general, there were no significant effects of the tillage treatments on cotton or wheat yields, but, at least, the initial yield loss commonly observed in the first years after introduction of conservation tillage could not be found here, while clear savings in operational costs were achieved. Consequently, a cumulative gross margin (GM) analysis showed higher gross margins in all conservation agriculture practices as compared to the control (conventional tillage). The values were highest under intermediate tillage with crop residues (UZB 1,288,000 = USD 1074), followed by zero tillage without crop residues (UZS 1,177,000 = USD 980) and permanent beds without crop residues (UZS 1,158,000 = USD 965).Dominance analysis revealed the clear advantage of the conservation practices over conventional tillage because of the higher total variable cost and lower GM.  Thus, adopting conservation agriculture practices on the degraded soils of Central Asia can improve cotton and winter wheat production and make it more profitable to farmers.


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