Kienzler, Kirsten Maren: Improving the nitrogen use efficiency and crop quality in the Khorezm region, Uzbekistan. - Bonn, 2010. - Dissertation, Rheinische Friedrich-Wilhelms-Universität Bonn.
Online-Ausgabe in bonndoc:
author = {{Kirsten Maren Kienzler}},
title = {Improving the nitrogen use efficiency and crop quality in the Khorezm region, Uzbekistan},
school = {Rheinische Friedrich-Wilhelms-Universität Bonn},
year = 2010,
month = jul,

volume = 72,
note = {In the irrigated agriculture of Central Asia, low nitrogen (N) fertilizer use efficiency in cotton (Gossypium hirsutum L.) and winter wheat (Triticum aestivum L.) decreases yields and farm income. Current N-fertilizer use is based on recommendations from Soviet times when fertilizer supply was subsidized to maximize production at all costs. Modern N management needs to enable farmers to obtain stable crop yields of good quality and preserve the environment. The present study, based on field experiments conducted 2004-2006 in the Khorezm region, Uzbekistan, intended to (i) establish cotton and wheat yield and quality responses to N fertilization; (ii) evaluate N-fertilizer use efficiency of officially recommended N use and farmers’ practice; (iii) simulate soil N dynamics and yields under varying N rates, irrigation water quantities and groundwater levels with CropSyst; and (iv) determine the financial feasibility of different N practices. The study included labeled N fertilizer (15N) experiments in 2005 to quantify the fate of the applied N fertilizer.
Although N was the most limiting nutrient, the N response curve of cotton and wheat yield to increasing N rates was rather flat with a yield maximum at 120 and 180 kg N ha-1, respectively. This can be attributed to unaccounted N supplements from ground- and irrigation water of around 31 kg ha-1. The official N recommendations of 200 and 180 kg N ha-1, for cotton and wheat respectively, corresponded well with both the measured and simulated N uptake at yield maximum. However, at this rate, the opening of cotton bolls was delayed beyond the period during which the ginneries offer the highest prices for cotton.
Total N-use efficiency was very high for both crops (81-84 %). The large share of soil-15N (48 and 47 %, respectively) indicates that immobilization processes and/or pool substitution strongly influenced recovery rates. Farmers’ N fertilization practice gave highest cotton yields, but around 22 % lower total 15N recovery rates (64 %). For wheat, an additional late N application at the heading stage yielded highest total 15N recovery rates (52 and 53 % in plant biomass and the soil, respectively). N fertilization with diammonium phosphate before seeding showed the highest N-use efficiency for wheat and cotton as compared to urea fertilizer.
Cotton fiber quality was of lowest grade (i.e. 31 mm length, 25 g tex-1 strength, and 4.08 micronaire) and remained unaffected by N treatments, timing of applications or N-fertilizer types. Fertilized with the recommended N amount, protein and gluten content of wheat kernels (12.3 and 23.0 %, respectively) met the criteria of only satisfactory to good wheat filler and low to medium flour thickener. Increasing N rates enhanced kernel protein (15 % at 300 kg N ha-1), but not gluten content (25.0 %). Protein content and yield were negatively related, showing the need for breeding or introducing wheat varieties with narrower quality and yield potential suitable for irrigated conditions in Uzbekistan.
The cotton-generic routine developed for the CropSyst model predicted the experimental yields with a high accuracy (RSME 1.08 Mg kg-1). Simulations show that gaseous N losses can be reduced by lowering the groundwater level. Increasing cotton yields without increasing N losses seems possible when matching water demand and supply more closely.
For cotton, returns to N investments were highest (1,069,332 UZS ha-1 net benefit) for the farmers’ N practice and for N rates below 120 kg ha-1, which encouraged fast maturation of cotton bolls at pick 1 and 2. The economic optimum thus diverged from the plant-N demand and recommendations of 200 kg ha-1. The economically most promising wheat treatments were those fertilized with the recommended N rate of 180 kg ha-1 and those receiving additional N just before anthesis (340,669 UZS ha-1 net benefit). However, the present reimbursement system at the mills lacks attractive quality-based incentives to encourage high quality production. Overall, the N management and N-use efficiency in irrigated cotton and wheat production can be improved by changing the payment system of the ginneries and mills to encourage sustainable N practices and increase crop quality. Wheat quality can be further enhanced through late N application, or by (breeding for) better varieties. CropSyst could demonstrate the impact of different agricultural practices on cotton yields and soil parameters and thus can help identifying changes in the current management system.},

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