Improving Nitrogen Fertilizer Use Efficiency in Surface‐ and Overhead Sprinkler‐Irrigated Cotton in the Desert Southwest

Abstract

Nitrogen fertilizer use efficiency (NUE) is low in surface-irrigated cotton (Gossypium hirsutum L.), especially when adding N to irrigation water. A NO 3 soil-test algorithm was compared with canopy reflectance-based N management with surface-overhead sprinkler-irrigation in central Arizona. The surface irrigation studies also compared fertigation of N fertilizer with knifing-in of N and the addition of a urease and nitrification inhibitor (Agrotain Plus, Koch Agronomic Services, Wichita, KS) to urea ammonium nitrate (UAN). Cotton lint and seed yields responded positively to N fertilizer in all four site-years. Recovery efficiency (RE) of N at low N fertilizer rates (60 to 76 kg N ha-1) ranged from 21 to 61% with surface irrigation and from 81 to 97% with overhead sprinkler irrigation. Deep percolation below 1.8 m was 4 to 11% of applied surface irrigations and rain, but was undetectable in the overhead sprinkler. Leaching of NO 3 was apparently the largest N loss pathway in the surface-irrigated system. Fertigating UAN into surface irrigation resulted in similar lint yields and RE as knifing UAN. Use of Agrotain Plus with UAN gave similar yields and RE as using UAN alone. Reflectance-based N management using normalized difference vegetation index-amber (NDVIA) saved 50% of N fertilizer of the full soil-test based dose without a yield reduction in three of four site-years. Nitrogen fertilizer was over-prescribed with the soil-test-based treatment. This may have been due to not accounting for N mineralization, which the reflectance method indirectly measures.

Which active optical sensor vegetation index is best for nitrogen assessment in irrigated cotton?

“…Canopy reflectance was measured weekly using the Crop Circle ACS‐470 AOS (Holland Scientific Inc., Lincoln, NE), starting about 2 wk after plant emergence and ending about mid‐bloom in two N management irrigated cotton studies in Maricopa, AZ (33.067 N, 111.97 W and 360 m above sea level) on a Casa Grande sandy loam (fine‐loamy, mixed, superactive, hyperthermic, Typic Natrargid); an overhead sprinkler irrigation (OSI) study, 2014–2015 (Bronson et al., 2017b), and a subsurface drip irrigation (SDI) study, 2016–2018 (Bronson et al., 2019). In the OSI study, there were eight N treatments replicated four times, described in detail in Bronson et al.…”

“…In the OSI study, there were eight N treatments replicated four times, described in detail in Bronson et al. (2017b). In the SDI study there were five N treatments (two of these at a deficit 70% irrigation level) replicated three times as described in Bronson et al.…”

“…In the OSI study, the reflectance‐based N plots initially received 50% of the N rate of the soil test plots. If NDVIA from reflectance plot means fell significantly below the plot mean of NDVIA of the soil test‐based N treatments, then the N rate was increased to match the soil test rate (designated “reflectance‐based N‐1″ in Bronson et al., 2017b). In the SDI study, we used NDRE instead of NDVIA to base the same reflectance plot N treatment approach on (Bronson et al., 2019).…”

“…Leaves, stems, seed, and burrs were analyzed for N content on the Leco CN analyzer. Lint and seed yields were sampled by a cotton picker on the center two rows on a 6‐m length, centered on the DGPS points (Bronson et al., 2017b, 2019).…”

Nitrogen Consumption and Productivity of Cotton under Sensor‐based Variable‐rate Nitrogen Fertilization

“…It was generally accepted that applying side‐dress N based on optical sensing measurements is conducive to reduce N fertilizer input and increase NUE. Sensor‐based N management using NDVI‐amber saved 50% of N fertilizer of the full soil‐test based dose without reducing cotton yield in 3 of 4 LYs (Bronson et al, 2017). Raun and Johnson (1999) stated that sensor‐based VNMS reduced N loss via surface runoff, volatilization, and leaching resultant from excessive pre‐plant N application, and increased NUE by up to 85% on cereal.…”