2012 Annual Report
Nitrogen treatment Fertilization mode/source Notes Zero-N Soil test-based N Knife/Urea amm. nitrate In two splits, four-leaf and first bloom Soil test-based N Fertigate/Urea amm. nitrate In two irrigations, first square & first-bloom Soil test-based N Fertigate/amm. sulfate In two irrigations,first square & first bloom Reflectance-based N Knife/Urea amm nitrate In two splits, first-squre and first bloom Reflectance-based N Fertigate/Urea amm. nitrate In two irrigations, first square & first bloom
The experimental design will be completely randomized block, with three replicates. Transects of soil profile (0 – 180 cm in 30 cm increments) NO3-N will be determined after the two fertilization/fertigation events on four, unreplicated plot-treatments, i.e. treatments 1, 2, 3, and 4. Transects will consist of 12 samples at 12 m intervals. Surface flux of N2O will be measured weekly for 10 weeks during the season using vented chambers and gas chromatography. Biomass and total N uptake will be determined plants on 2 m of row at first open boll. Nitrogen recovery efficiency, physiological N use efficiency and agronomic use efficiency will be calculated. Lint and mature seed yields will be machine harvested. Mature cotton seed N will be determined from grab samples at the four DGPS points per plot and the percentage of seed N to total N uptake calculated. Micronaire and other fiber quality attributes will be determined on lint and the relationships of these to N fertilizer rate estimated. Soil sampling for extractable NO3-N from 0 to 180 cm will be done after harvest to assess residual and NO3 and leached NO3 (90 – 180 cm profile NO¬3). Post-harvest soil sampling will on four samples per plot to assess the spatial variation of leached NO3 across the plot. Transect soil NO3 data will be subject to repeated measured ANOVA, repeated by depth and by latitude. Pre-plant and harvest soil profile NO3, N2O emission, NDVI, plant biomass, plant N uptake, lint, and seed yield will be analyzed with a mixed model using SAS. Replicate will be considered random, and N treatment will be considered fixed. The four subsamples per plot will be averaged by plot in the mixed analysis to produce least square means, but longitude, latitude and longitude*latitude will be covariates.