Nitrogen Management for Subsurface Drip Irrigated Cotton: Ammonium Thiosulfate, Timing, and Canopy Reflectance

Abstract

In subsurface drip irrigation (SDI) systems, water constraints to cotton (Gossypium hirsutum L.) production are greatly minimized and N management becomes the main priority. Injecting N fertilizer into SDI systems should, in theory, be as efficient as the irrigation delivery system itself. The objective of this study was to test duration of N injections, addition of the nitrification inhibitor ammonium thiosulfate (ATS), and using canopy spectral reflectance to guide N injections in a 2‐yr study of SDI cotton in Lubbock, TX. For a 1400 kg ha−1 expected lint yield, the N fertilizer rate was 170 kg N ha−1 minus the 0‐ to 0.6‐m soil NO3–N and an estimate of irrigation water NO3 (20 and 30 kg N ha−1 for 2005 and 2006). We tested injection of urea–NH4NO3 (UAN) between first square and early bloom, and first square and peak bloom. There was no effect of timing or ATS on lint yield. Reflectance‐based N management up to peak bloom resulted in savings of 28 and 17 kg UAN‐N ha−1 for 2005 and 2006, respectively, compared with soil‐test‐based N fertigation. Lint yields were similar between reflectance‐based UAN management (1814 kg ha−1) and UAN injected up to peak bloom based on soil test NO3 (1880 kg ha−1). Nitrogen fertilizer recovery at first open boll was not affected by treatment but was high (62–75%). Flux of N2O + N2 was low (800–2100 g N ha−1) in both years and was not different between fertilized and unfertilized plots. Residual 0‐ to 1.2‐m soil profile NO3 after 2 yr was not affected by N fertigation treatments. Nitrogen fertilizer injections in SDI cotton are utilized very efficiently, and spectral‐reflectance‐based approaches have potential to reduce N fertilizer inputs.

Inter-relationships of cotton plant height, canopy width, ground cover and plant nitrogen status indicators

“…This greatly reduces the usefulness of petiole NO 3 . Yabaji et al (2009) reported that N fertilizer applications in SDI-irrigated cotton in West Texas are not effective after mid-bloom.…”

Quantifying Greenhouse Gas (CO2, CH4, and N2O) Fluxes from Soil in a Pasture

“…They achieved the best predictions by using reflectance ratios of the area of interest relative to a wellfertilized area. Yabaji et al 20 reported that basing in-season SSNM of drip-irrigated cotton on canopy reflectance resulted in 17-28 kg N ha-' savings in N fertilizer compared to regional N recommendations, without reducing lint and seed yields. Bronson et aJ.24 compared variable-rate N applications based on grid soil sampling to blanket regional N management in a 3-year study of center-pivot irrigated cotton.…”

Use of Nitrogen Calibration Ramps and Canopy Reflectance on Farmers' Irrigated Cotton Fields

“…Several field plot studies in West Texas used canopy refiectance based indices to assess in-season N status of cotton in SDI, and center-pivot fields in the SHP (Li et al, 2001;Chua et al, 2003;Bronson et al, 2003aBronson et al, , 2005Bronson et al, , 2011Yabaji et al, 2009). Reflectance-based N management was tested and resulted in less N fertilizer use than the regional soil test-yield goal based N management, without hurting yields (Chua et al, 2003;Yabaji et al, 2009;Bronson et al, 2011).…”

“…Reflectance-based N management was tested and resulted in less N fertilizer use than the regional soil test-yield goal based N management, without hurting yields (Chua et al, 2003;Yabaji et al, 2009;Bronson et al, 2011). Previous studies in corn on the use of canopy reflectance to assess in-season N status reported that a well-fertilized reference plot or strip is mandatory to compare reflectance in the area of interest to (Varvel et al, 1997;Solari et al, 2008;Scharfand Lory, 2009;).…”

“…The sufficiency index was first proposed by Peterson et al ( 1993) for use with a chlorophyll meter in corn, but has been used in other crops as well such as rice (Hussain et al, 2000). Previous West Texas cotton studies also used a well-fertilized reference (Chua et al, 2003) and then the regional soil test-yield goal recommendation (Yabaji et al, 2009;Bronson et al, 2011 ) as the reference in calculating a sufficiency index.…”