1a. Objectives (from AD-416):
1. Compare urea ammonium nitrate (UAN) fertigation with knife applications of UAN in furrow-irrigated cotton. 2. Compare soil test-based N fertilizer management with canopy reflectance-based N management in furrow-irrigated cotton. 3. Construct N balances for furrow-irrigated cotton, i.e. quantify total N uptake, recovery N use efficiency, NO3 leaching, and denitrification losses. 4. Compare urea ammonium nitrate (UAN) fertigation with ammonium sulfate fertigation for a farm-scale surface-irrigated field, furrowed for cotton.
1b. Approach (from AD-416):
In February, 2012, pre-plant soil sampling to 180 cm for NO3 will be done on four samples per plot. Cotton will be planted in April, 2012 in plots that will be 8, 1-m rows wide by 180 m. At harvest, soil sampling to 180 cm for nitrate will on eight samples per plot. Nitrogen treatments will include: 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.
3. Progress Report:
This project is directly related to objective 3 of the parent project: "Develop and evaluate decision support systems that integrate remote sensing, geographical information systems, and crop growth modeling for assessing crop water and nutrient management alternatives at field-level and watershed scales". In the 2011 summer growing season of Central Arizona, we completed the first year of field and supporting laboratory work on this new project. High initial soil nitrate-N levels precluded a N-fertilizer response in yields. Nitrous oxide emissions were very low, which are welcome results, since N2O is a powerful greenhouse gas. We could not calculate N fertilizer recovery efficiency since zero-N yields were not different from N-fertilizer yields. We did calculate a study average internal N use efficiency of 7 kg lint per kg N in plant. We plan to repeat this study in 2012 after a winter barley cover crop to reduce soil nitrate.