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United States Department of Agriculture

Agricultural Research Service

Research Project: REMOTE SENSING FOR CROP AND WATER MANAGEMENT IN IRRIGATED AGRICULTURE Title: Use of nitrogen calibration ramps and canopy reflectance on farmers' irrigated cotton fields

Authors
item Bronson, Kevin
item Malapati, T -
item Wheeler, C. -
item Brown, R -
item Taylor, R -
item Scharf, P -
item Barnes, E -

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 10, 2011
Publication Date: February 17, 2012
Citation: Bronson, K.F., Malapati, T.A., Wheeler, C.M., Brown, R.K., Taylor, R.K., Scharf, P.C., Barnes, E.M. 2012. Use of nitrogen calibration ramps and canopy reflectance on farmers' irrigated cotton fields. Soil Science Society of America Journal. 76(3):1060-1067.

Interpretive Summary: Nitrogen is the main nutrient constraint to cotton (Gossypium hirsutum L.) production in the southwestern U.S. However, N fertilizer recovery in cotton is usually low. Previous research in West Texas has demonstrated the potential of canopy level spectral reflectance to assess need for in-season N in irrigated cotton. Reduced N fertilizer applications and reduced residual soil NO3--N resulted from reflectance-based N management, without sacrificing yield. However, remote sensing for in-season N management in cotton has not been tested on-farm. The objective of this research was to test a calibration ramp approach to determining optimum in-season N fertilizer rates in irrigated cotton in West Texas. Normalized difference vegetative index (common reflectance index which uses visible and near infrared reflectance) at mid bloom and at peak bloom were positively related to N fertilizer rate in only one ramp in each year. These ramps also had significant N fertilizer rate response in lint yield and N rate. Few ramps with significant N rate effects was due to the level of pre-plant soil profile NO3 at the sites and since the N calibration ramps were super-imposed on the farmers’ N management. Significant relationships were observed for mid bloom NDVI and lint yield as well as peak bloom NDVI and lint yield across all ramps. Good relationships between NDVI and yield are a foundation some N fertilizer recommendation algorithms. Although this study focused on N management, the strong relationships between NDVI and lint yield implies some crop management uses of canopy reflectance besides N fertilizer. These potentially include in-season applications of growth regulators and end-of-season harvest aids.

Technical Abstract: Nitrogen is the main nutrient constraint to cotton (Gossypium hirsutum L.) production in the southwestern U.S. However, N fertilizer recovery in cotton is usually < 50 %. Our previous research in West Texas has demonstrated the potential of canopy level spectral reflectance to assess need for in-season N in irrigated cotton. Reduced N fertilizer applications and reduced residual soil NO3--N resulted from reflectance-based N management, without sacrificing yield. However, calibration of remote sensing indices such as normalized difference vegetative index (NDVI) to need for N fertilizer is difficult. Typically, well-fertilized plots or strips are used to reference NDVI or chlorophyll meter data in the crop area of interest in corn and other crops. However, in cotton over-fertilization can result in rank growth and reduced lint yields. Recently, Oklahoma State University developed a crop reflectance calibration procedure of using multiple N rate calibration plots, or a ramp approach for wheat and corn. We tested this approach in irrigated cotton fields in Lubbock County Texas in 2008 and 2009. The main objective of this research was to test a calibration ramp approach to determining optimum in-season N fertilizer rates in irrigated cotton in West Texas. Normalized difference vegetative index at mid bloom and at peak bloom were positively related to N fertilizer rate in only one ramp in each year. These ramps also had significant N fertilizer rate response in lint yield and N rate. Few ramps with significant N rate effects was due to the level of pre-plant soil profile NO3 at the sites and since the N calibration ramps were super-imposed on the farmers’ N management. Significant relationships were observed for mid bloom NDVI and lint yield as well as peak bloom NDVI and lint yield across all ramps. Good relationships between NDVI and yield are a foundation some N fertilizer recommendation algorithms.

Last Modified: 10/31/2014
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