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United States Department of Agriculture

Agricultural Research Service

Research Project: REMOTE SENSING FOR CROP AND WATER MANAGEMENT IN IRRIGATED AGRICULTURE

Location: Water Management and Conservation Research

Title: Canopy Reflectance-Based Nitrogen Management Strategies for Subsurface Drip Irrigated Cotton in the Texas High Plains

Authors
item BRONSON, KEVIN
item Malapati, Adi -
item Scharf, Peter -
item Nichols, Robert -

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: January 25, 2011
Publication Date: January 26, 2011
Citation: Bronson, K.F., Malapati, A., Scharf, P.C., Nichols, R.L. 2011. Canopy reflectance-based nitrogen management strategies for subsurface drip irrigated cotton in the Texas High Plains. Agronomy Journal. 103(2):422-430.

Interpretive Summary: Nitrogen (N) fertilizer management in subsurface drip irrigation (SDI) systems for cotton (Gossypium hirsutum L.) can be very efficient when N is injected with the irrigation water (fertigated) on a near daily basis. However, the daily rates and total amounts of N fertigation are uncertain. Normalized difference vegetative index (NDVI), calculated from weekly canopy reflectance measurements may guide N management. The objective of this 3-y. study on an Acuff sandy clay loam near Lubbock, TX, was to test two canopy reflectance strategies for estimating and adjusting injection rates of urea ammonium nitrate (UAN) fertilizer between first square and early-mid bloom. We also evaluated three N rates; 50, 100, and 150 % of the soil test-based N recommendation for a 1400 kg lint ha-1 estimated yield. In the reflectance-based N strategy-1 (RN1), UAN was injected starting at first square at 50 % of the soil test N rate. When NDVI in RN1 fell significantly below NDVI of 100 % soil test N, the UAN injection rate was increased to match the injection rate of the soil test plots. The reflectance-based N strategy-2 (RN2) had an initial UAN injection rate equal to that of the soil test N, and was raised to match the 150 % soil test N based on NDVI. Nitrogen rates for the RN1 across 3 yr were 22 kg N ha-1 less, or 31 % less than the soil test treatment, without hurting lint or seed yields. In 2007, N rates with RN2 were 11 kg N ha-1 higher than the soil test N rate, without any yield benefit. This study confirms that the “N-savings” approach of RN1 can reduce SDI cotton fertilizer use, without sacrificing yield. It is likely that the same approach can be used with N fertigations for cotton in center-pivots as well.

Technical Abstract: Nitrogen fertilizer management in subsurface drip irrigation (SDI) systems for cotton (Gossypium hirsutum L.) can be very efficient when N is injected with the irrigation water (fertigated) on a daily basis. However, the daily rates and total amounts of N fertigation are uncertain. Normalized difference vegetative index (NDVI) calculated from weekly canopy reflectance measurements can guide N management in SDI cotton. The objective of this 3-year study (2007-2009) on an Acuff sandy clay loam (fine-loamy, mixed, superactive, thermic Aridic Paleustolls) near Lubbock, TX, was to test two canopy reflectance-based strategies for estimating and adjusting injection rates of urea ammonium nitrate (UAN) fertilizer between first square and early mid-bloom. We also evaluated three N rates; 50, 100, and 150% of the soil test-based N recommendation for a 1400kg lint ha-1 yield goal. In the reflectance-based N strategy-1(RN1), UAN was injected starting at first square at 50% of the soil test N rate. When NDVI in RN1 fell significantly below NDVI of plots with 100% soil test N, the N injection rate was increased to match the injection rate of the 100% soil test plots. The reflectance-based N strategy-2 (RN2) had an initial N injection rate equal to that of the 100% soil test N, and was raised to match the 150% soil test N based on NDVI. Nitrogen rates for the RN1 averaged across 3 yr were 22 kg N ha-1 less, or 31% less than the soil test treatment, without hurting lint or seed yields. In 2007, N rates with RN2 were 11 kg N ha-1 higher than the soil test N rate, without any yield benefit. Economic optimum N rates for lint production ranged from 23 kg N ha-1 in 2009 to 75 kg N ha-1 in 2008.

Last Modified: 9/29/2014
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