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Fluid Journal : Fall 2014
4 The Fluid Journal Fall 2014 Canopy reflective indices used to examine plant available K. A Look At Potassium Deficiency in Cotton The Fluid Journal • Official Journal of the Fluid Fertilizer Foundation • Fall 2014 • Vol. 22, No. 4, Issue #86 Cotton has been labeled as a poor extractor of soil potassium (K) as compared to other more fibrous rooted crops, particularly with respect to K located near the surface. These root characteristics, coupled with the inherent stratification of K in production agriculture and the increased K demand from higher- yielding and earlier-maturing cotton cultivars currently grown across the US Corn Belt, frequently result in K deficiencies appearing in the later- flowering or early boll-filling periods. These deficiencies are of interest from a remote-sensing standpoint for a couple of reasons: • First, early diagnosis of the K deficiency from a ground-based reflection unit could potentially drive an ameliorating application of K to the soil (if early enough in the growing season) or as a foliar application of K. This could drastically reduce or potentially remove the yield penalty associated with the deficiency, increase efficiency of the fertilizer, and thereby increase the profitability. • Second, the occurrence of K deficiencies in the upper canopy of a cultivar’s particular reflectance properties could influence other remote-sensing activities, such ▼ DOWNLOAD Tyson Raper, Derrick Oosterhuis, Leo Espinoza and Taylor Coomer Summary: The data from this research suggest the that use of some cultivar adjustment factor will have to be implemented if sufficiency reflectance datum is collected on a nearby field of a different cultivar or if a threshold value approach is used to drive variable rate nitrogen (N) applications. Additional research is needed to better characterize index responses in soils of lower K status or under seasons that are more favorable for the development of K deficiencies. as the diagnosis of N stress and potential amelioration alternatives. Objective The objective of this research was to examine the response of two reflectance indices, calculated from measured reflectance in the red, red-edge, and near–infrared spectral regions, to changes in cultivar and plant-available K. Site/Treatment/Analysis Block trial. A randomized strip, complete block trial with five replications was conducted in 2012 and 2013 at the Lon Mann Cotton Research Center located in Marianna, AR. Soil samples were collected from bed shoulders at 6-inch depths from each plot on 31 January 2012 and analyzed (Mehlich-3 extraction) by the University of Arkansas Soil Testing Laboratory. Treatments consisted of 0, 30, 60, and 90 lbs/A of K2O applied to Phytogen 499 WRF (PHY499), Stoneville 5458 B2RF (ST5458) and DeltaPine 0912 B2RF (DP0912) varieties within three weeks of planting (Figure 1). Regression analysis tested the response of seed-cotton yield and index readings to changes in available K2O. Available K. The calculated amount of available K was chosen in lieu of applied K fertilizer rate due to initial differences in soil K concentrations. Plant available K2O was calculated as [(ppmsoiltestKx2x1.2)+lbK2O fertilizer/acre] where 1.2 is the factor for converting K to K2O and 2.0 is the factor for converting ppm to lbs/A assuming 2 million lbs soil/A furrow slice. Reflectance Reflectance was measured at two- week intervals beginning at flowering with the Crop Circle ACS-470 (Holland Scientific Inc., Lincoln, NE) [Figure 2]). Analysis for 2012 was conducted on data collected 7 August and 22 August 2012, as consistent K deficiencies across the trial were only noted by 22 Figure 1. Image of cotton plots with muriate of potash (0-0 -60) prills on soil surface.