Spatial relationships between the van Genuchten soil-water retention curve parameters and photosynthetic gas exchange variables in a wheat field

Photosynthetic gas exchange indices can be used to assess spatial variation of crop growth and yield on the field. Spatial variation of soil parameters can be an important tool to assess and manage crop growth status and product quality in the field, given the impact of soil on photosynthetic function. The purpose of this study was to evaluate the spatial relationships between the van Genuchten (vG) soil water retention curve parameters, soil properties and the photosynthetic gas exchange indices in a wheat field with an extension of 200 ha. Different variables of soil and plant were determined at the 100 nodes of a nearly regular grid (150 m × 150 m) over the whole field. The range of variograms showed high variability for photosynthetic parameters and vG parameters, and greater continuity for soil parameters. Photosynthesis was significantly correlated with saturated soil water content (θs) (r = 0.26*), θ1500kPa (permanent wilting point) (0.21*), porosity (r = 0.31**), bulk density (r = −0.32**) and clay content (r = 0.24*). Cross correlogram and linear model of coregionalization of sub-stomatal CO2 concentration (Ci) and stomatal conductance (gs) with photosynthetic rate (A) and transpiration (E) showed opposite relation with soil and hydraulic properties. Regressing of maps showed that a large part of the total variation in A (66%), Ci (79%) and gs (37%) was explained by soil variables. Also, from the visual inspection of the interpolated maps the field can be divided in zones characterized by different soil properties and these maps could be effectively used by farmers to improve wheat yield. On the other hand, results of this study may enhance understanding of the soil properties and soil hydraulic parameters effects on gas exchange parameters of the plant and delineation of the field in homogeneous zones that could be advantageously used by farmers to make informed decisions in site-specific management.