Wednesday, November 7, 2007 - 10:45 AM
295-5
Influence of Nitrogen Sources and Timing on Fertilizer Uptake Efficiency of Irrigated Cotton (Gossypium hirsutum L.) in Central Asia.
Nitrogen (N) is considered one of the most limiting nutrients in cotton (Gossypium hirsutum L.) production in Central Asia (CA). In the irrigated regions of Uzbekistan, the efficiency of N-fertilizer use is particularly important as poor N-management leads to losses to the environment via denitrification or leaching, directly causing a decrease in farmers’ yield and income. So far, N-deficiencies are met by applying the most affordable N-fertilizers available. Therefore, this study examined the N-fertilizer efficiency under current cotton production practices to optimize its use while minimizing environmental impacts. Cotton was planted in micro-plots on a medium loamy gleyic Arenosol in 2005. A single rate of 120 kg N ha-1 was applied. Four fertilizer regimes varying in N-source (DAP+Urea, Urea-only, DAP+NH4NO3) and three split-application times, (before seeding; at 2-4 leaves or budding; flowering) were analyzed. 15N-labeled fertilizer was used to quantify N uptake in plant fractions and 0-60cm soil layers. Across all plots, total recovery of 15N-fertilizer in the soil averaged 58% (±9.7%), and in the above ground biomass 35% (±3.6%). Irrespective of timing and N-source, highest fertilizer 15N in the soil was recovered from the top 0.1m layer. Of the plant fractions examined, cotton seeds and leaves always reflected the fertilizer N applied. Soil and plant 15N recovery was significantly affected by N-timing, N-source and its combinations. Highest soil 15N was recovered from the Urea-only regime at any time during the growing season, proving it to be the most immobile N-fertilizer under irrigated conditions. The DAP+NH4NO3 plots showed significantly (p<0.05) lower 15N content at budding and flowering than the Urea-only plots, indicating N-losses via leaching or denitrification. It is therefore argued that in future mainly urea-N be applied in irrigated cotton production in CA instead of NO3–containing fertilizers thus reducing environmental pollution and farmers’ costs.
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