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

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‐yr 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 1400 kg 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.

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

“…The site was planted on 20 May 2010 with Stoneville 5458 (ST 5458) and FiberMax 9180 (FM 9180) in 8, 1-m row plots that were 180 m long. There were 3 levels of N fertilizer in New Deal, a zero-N, intermediate N (50 kg ha −1 ) and full N rates (101 kg ha −1 ) determined as the first reflectance-based N strategy described in Bronson et al (2011). Each block consisted of 8 rows that were supplied by an individual irrigation and fertilizer injection station.…”

Relationship of cotton nitrogen and yield with Normalized Difference Vegetation Index and plant height

“…Gutierrez et al (2012) found that the correlation of cotton lint yield with NDVI was not significant at pinhead square, mid-bloom, or cut out (R 2 = 0.00-0.02) but was significant at early bloom and peak bloom (R = 0.46-0.69) in Arizona. Bronson et al (2011) reported that cotton lint yield was significantly correlated with amber and red DDVI at early bloom with R 2 = 0.06-0.30 and at mid-bloom with R 2 = 0.07-0.35 in Texas during 2007-2009. Bronson et al (2003) observed that the correlation of cotton lint yield with red NDVI was insignificant at early square, early bloom, or peak bloom at Ropesville, Texas in 2000, but was significant at early square, early bloom, and peak bloom with R 2 = 0.34-0.53 in 2000, and was insignificant at early square, but significant at early bloom and peak bloom with R 2 = 0.21 and 0.55, respectively, in 2001 at Lubbock, Texas.…”

“…Raper et al (2013) observed that the R 2 values of cotton leaf N concentration with NDVI from three different sensors (Crop Circle ACS-210, GreenSeeker Model 505, and Yara N Sensor) were between 0.08 and 0.69 in 2008, 0.06 and 0.72 in 2009, and 0.12 and 0.77 in 2010 during pre-square to peak bloom in Mississippi. Bronson et al (2011) reported that leaf N was significantly correlated with amber and red NDVI at early bloom with R 2 = 0.27-0.59 and mid-bloom with R 2 = 0.07-0.38 on irrigated corn in Texas during 2007-2009. Bronson et al (2003) found that the correlation of cotton leaf N concentration with red NDVI was insignificant at early square, early bloom, or peak bloom at Ropesville, Texas in 2000, but was significant at early square, early bloom, and peak bloom with R 2 = 0.18-0.19 in 2000, and was insignificant at early square, but significant at early bloom and peak bloom with R 2 = 0.…”

Precision Nutrient Management and Crop Sensing

“…Zhao et al (2005) found that leaf chlorophyll was closely related to reflectance ratios using either R 708 /R 915 or R 551 /R 915 wavebands and there was a linear relationship between leaf nitrogen content and the reflectance ratio of R 517 /R 413 . In a subsequent study based on the observations from their original study, Bronson et al (2011) found that when NDVI values in the field decreased below a nitrogen-rich area and nitrogen was added to the treatment areas, there was a reduction in the amount of nitrogen applied by 33 % with no impact on lint or seed yield. They also found that the EONR varied from 23 to 75 kg·N·ha À1 among the 3 years of their study suggesting that the nitrogen response will differ among years due to growing conditions.…”