Evaluating the Effects of Soil Variability on Rice and Soybean Production with Veris EC a

Transcription

1 RICE CULTURE Evaluating the Effects of Soil Variability on Rice and Soybean Production with Veris EC a Mapping C. Jayroe, W.H. Baker, A. Greenwalt, and G. Bell ABSTRACT Soil variations can be a direct source of yield differences due to the diverse ratios of sand, silt, and clay, which each conduct electricity at their own individual levels (Lund et al., 1999). These variances affect the water-holding capacity, nutrient leaching, and plant root stability in soils. It is believed that the electrical conductivity of a soil is a function of its water and/or salt content, as well as the soil structure, texture, and mineralogy (Nadler and Frenkel, 1980). In this study, specific attention was directed to the effects of soil texture changes on yield and plant productivity, since one of the primary factors affecting the availability of water and nutrients is the soil-specific texture and structure (Kitchen et al., 1999). INTRODUCTION Electrical conductivity (EC a ) was measured over an Arkansas rice-soybean production field with a Veris EC a. The main purpose of this study was to determine whether soil electrical conductivity field maps could display a direct relationship with crop productivity. EC a is the designation for a soils apparent electrical conductivity measurement (Rhoades and Ingvalson, 1971). This method is believed to be well-suited to precision agriculture due to its large volume of measurement, which reduces the influence of local scale variability (Corwin and Lesch, 2003.) 262

2 B.R. Wells Rice Research Studies 2003 PROCEDURES The field observed in this study was selected based on its diverse soil characteristics due to land-shaping activies. The Veris EC a was used to map the various portions of sand, silt, and clay. Measurements were acquired continuously along parallel paths spaced approximately every 20 meters. The measurements were simultaneously associated with coordinates using a DGPS. Later these points were interpolated using a GIS as an inverse distance weighted surface. The results of the interpolation were compared with yield data and multispectral imagery acquired during vegetative growth. RESULTS AND DISCUSSION Veris EC a mapping has shown potential for establishing management zones on farms with significant soil variation. In this study a direct correlation was not found between textural changes (Fig. 1) and final rice yield (Fig. 2). The contour lines drawn from the Veris map were used to distinguish areas where land leveling had taken place in previous years (Fig. 1). Rice yield (Fig. 2) was relatively unrelated to textural changes. Soybean yield (Fig. 3) did mimic these areas within the Veris contours. Significant yield reductions were a result of these "cut areas" for the soybean crop but were not noted for rice yield. Rice canopy reflectance recorded on 21 June 2003 with a multispectral aerial image displayed a similar pattern in early vegetative growth (Fig. 4). Thus, while final rice yield did not show a reduction in productivity, the early vegetative biomass (vigor) was impaired in these same regions of the field. SIGNIFICANCE OF FINDINGS Better crop management decisions can be made by understanding the soil characteristics of a field. For instance, soil sampling can be more productive by adequately collecting samples from zones in the field that share similar physical characteristics. This would provide a much better allocation of fertilizer and other crop inputs. In this study, low-yielding soil cut areas could be mapped and then mitigated in a more effective manner. LITERATURE CITED Corwin, D.L.and S.M. Lesch Application of soil electrical conductivity to precision agriculture: Theory, principals, and guidelines. Agron. J. 95: Lund, E.D., C.D. Christy, and P.E. Drummond Practical applications of soil electrical conductivity mapping. Proc. 2nd European Conference on Precision Agriculture July Denmark. Kitchen, N.R., K.A. Sudduth, and S.T. Drummond Soil electrical conductivity as a crop productivity measure for claypan soils. J. Prod. Agric. 12:

3 AAES Research Series 517 Nadler, A. and H. Frenkel Determination of soil solution electrical conductivity from bulk soil electrical conductivity measurements by the four-electrode method. Soil Sci. Soc. Am. J. 44: Rhoades, J.D. and R.D. Ingvalson Determining salinity in field soils with soil resistance measurements. Soil Sci. Soc. Amer. Proc. 35: Fig. 1. Veris soil electrical conductivity EC a field map illustrating the cut portion of field. 264

4 B.R. Wells Rice Research Studies 2003 Fig. 2. Rice yield map grouped into yield classes. 265

5 AAES Research Series 517 Fig. 3. Soybean yield data grouped into yield classes. 266

6 B.R. Wells Rice Research Studies 2003 Fig. 4. Classified multispectral image of rice canopy acquired on 21 June