State-Space Description of Field Heterogeneity: Water and Nitrogen Use in Cotton

Li, H¹.  R.J. Lascano¹, J. Booker¹, L.T. Wilson², K.F. Bronson¹, and E. Segarra^1,3

¹Texas A&M University, Texas Agricultural Experiment Station, Lubbock, Texas

²Texas A&M University, Texas Agricultural Experiment Station, Beaumont , Texas

³Texas Tech University, Lubbock, Texas

Abstract

A 2-year (1998-1999) study was conducted on the Texas High Plains in the USA to determine the interdependence between management (irrigation and N fertilizer application), soil heterogeneity (texture, soil water, and NO3-N) and topography, and their impact on cotton (Gossypium hirsutum) lint yield and N uptake. Soil in the study area was classified as Aridic Paleustalfs (Amarillo sandy loam). Treatments were irrigation at 50 and 75% estimated cotton evapotranspiration (ET) and N rates at 0, 90, and 135 kg ha-1. Soil water content (SWC), lint yield, N uptake, and N fertilizer recovery, measured as a function of management and space, were higher on low positions. Mixed model analysis showed that irrigation was significant on SWC, lint yield, and N uptake (P<0.05) each year. The N treatment had no effect on lint yield or N uptake in 1998 because of high soil residual NO3-N, and the model residual was significant for all measured variables (P<0.0001). Sand, SWC, lint yield, and N uptake were negatively correlated with SE (rmore than or equal to -0.64). In 1998, lint yield, SWC, clay, sand, and SE were cross correlated within 60 to 80 m. Multivariate state-space analysis showed that lint yield at position i was weighted on lint yield, SWC, clay, sand, and SE at previous position i-1. It is concluded that 75% ET and N rate at 90 kg ha-1 would be the basis to consider variable water and N rates related to field conditions, and the state-space model quantified spatial interdependence between irrigation, fertilization, and field heterogeneity.

Reference:  Li, H., R.J. Lascano, J.  Booker, L.T. Wilson, K.F. Bronson, and E. Segarra.  2002.  State-space description of field heterogeneity: water and nitrogen use in cotton.  Soil Sci. Soc. Am. J. 66: 2, 585-595. .