Monday, November 5, 2007 - 1:00 PM
101-1

Use of Active Spectroradiometers to Assess to In-season Nitrogen Fertilizer Requirements for Cotton.

Kevin F. Bronson1, Randal Taylor2, William Raun2, Edward Barnes3, Toby S. Osborne4, Adinarayana Reddy Malapati5, Peter Scharf6, J.C. Banks2, and Jason Nusz7. (1) Texas A&M University - Texas AgriLife Research, 1102 E FM 1294, Lubbock, TX 79403, (2) Oklahoma State University, 111 Ag Hall, Stillwater, OK 74078, (3) Cotton Incorporated, Cotton Inc., 6399 Weston Parkway, Cary, NC 27513, (4) Oklahoma State University - Plant & Soil Sciences Dept, 16171 Hwy 283, Southwest Research and Extension Center, Altus, OK 73521, (5) Texas Agric. Exp. Stn, 1102 E FM 1294, Lubbock, TX 79403, (6) 214 Waters, University of Missouri, University of Missouri, Department of Agronomy, Columbia, MO 65211, (7) Plant and Soil Science, Texas Tech University, Goddard Hall, Lubbock, TX 79405

Canopy reflectance has potential in irrigated cotton (Gossypium hirsutum L.) as an indicator of need for in-season N fertilizer applications.  Texas has conducted studies where sensor-based N management consists of referencing NDVI to a soil test based treatment (N fertilizer plus 60-cm soil NO3 = 168 kg N/ha for a target yield of 1400 kg lint/ha) and to 1.5 times soil test N rate.  The ramp calibration strip (RCS) approach may be superior to a single well-fertilized reference plot or strip. Over-fertilization of cotton often results in rank growth and delayed maturity, so the RCS approach should be able to identify the optimum N rate.  Nitrogen calibration ramps (0 to 180 kg N/ha in 11 kg N/ha steps) were established at several sites in farmers' fields in West Texas and Oklahoma in 2007.  However, no differences in NDVI were observed using either the active spectroradiometers GreenSeeker or Crop Circle ACS-210, where the farmers applied N fertilizer.  In established small plot N fertilizer trials in West Texas, Western Oklahoma and the Bootheel of Missouri in 2005-2007, significant differences in NDVI were observed among N fertilizer treatments.  Lint yield correlated well to NDVI at several growth stages in the long-term cotton N fertilizer study at Lake Carl Blackwell in Oklahoma.  Optimum N rate was related to NDVI in Missouri between first square and first bloom.  Leaf N, biomass and plant height at early bloom correlated with NDVI in Texas.  In Texas and Missouri, NDVI from the passive sensor CropScan MSR 16 compared well with the active sensors.  The active sensors have the advantages of not requiring cloudless skies and not being sensitive to sun angle and time of day. 

Back to Active Sensors for Nutrient Management (includes Graduate Student Competition)
Back to S04 Soil Fertility & Plant Nutrition

Back to The ASA-CSSA-SSSA International Annual Meetings (November 4-8, 2007)