Submitted to: Open Journal of Soil Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/5/2013
Publication Date: 7/19/2013
Citation: Nelson, R., Lascano, R.J., Booker, J.D., Zartman, R., Goebel, T.S. 2013. Evaluation of the Precision Agricultural Landscape Modeling System (PALMS) in the semiarid Texas Southern High Plains. Open Journal of Soil Science. 3(4):169-181. Interpretive Summary: The applications of simulation models to investigate different aspects of the agronomy of crops have resurfaced in recent years. This renewed interest can be explained by several factors that include: 1) cost of computers has decreased and the speed of the processors, CPU, has increased almost in direct proportion; 2) simulation models require input data that now is readily available, e.g., weather and soils data; 3) theories of soil-plant-water relations developed in the 1950’s and 1960’s have been translated into mechanistic models; 4) the realization that agronomic studies have to be done at the appropriate scale, i.e., landscape; 5) incorporation of spatial and temporal statistics that led to the development of site-specific and/or precision agriculture; and 6) combination of simulation models with site-specific concepts to understand factors and their interactions to explain crop yield across the landscape. A simulation model that contains these features is the Precision Agriculture Landscape Modeling System (PALMS) developed by John Norman and co-workers at the University of Wisconsin. This model treats the field in a grid and the soil depth represents the third dimension. For example, a ¼ mile center pivot irrigation system covers approximately 51 ha and if this area is divided into grids of 10 m × 10 m (100 m2 area) this would represent 5100 cells. The significance is that a model such as PALMS calculates all processes for each cell and thus gives an estimate of crop yield for each cell, that is 5100 estimates of crop yield for a field irrigated with a ¼ mile center pivot. This allows using the model for many applications particularly for management of inputs. The PALMS model has been extensively used in the Midwest, particularly for applications of soil erosion and runoff, but has no been tested for soils of the Texas High Plains. Therefore our objective was to evaluate the performance of the model on calculating soil water content for the major soil types of the Texas High Plains. Our evaluation showed that when using the appropriate, and as expected, soil physical properties as input the PALMS model correctly calculates soil water content in the profile. This conclusion means that we can use PALMS to evaluate management of water, fertilizer and other inputs and their effect on crop yield. PALMS is a management tool that can be used to further increase the efficiency of limited water fro crop production in the Texas High Plains.
Technical Abstract: Accurate models to simulate the soil water balance in semiarid cropping systems are needed to evaluate management practices for soil and water conservation in both irrigated and dryland production systems. The objective of this study was to evaluate the application of the Precision Agricultural Landscape Modeling System (PALMS) model to simulate soil water content throughout the growing season for several years and for three major soil series of the semiarid Texas Southern High Plains (SHP). Accuracy of the model was evaluated by comparing measured and calculated values of soil water content and using root mean squared difference (RMSD), squared bias (SB), squared difference between standard deviations (SDSD), and lack of correlation weighted by the standard deviation (LCS). Different versions of the model were obtained by modifying soil hydraulic properties, including saturated hydraulic conductivity (Ks) and residual ('r) and saturated ('s) soil volumetric water content, which were calculated using Rosetta pedotransfer functions. These modifications were combined with updated routines of the soil water solver in PALMS to account for rapid infiltration into dry soils that often occur in the SHP. Field studies were conducted across a wide range of soil and water conditions in the SHP. Soil water content was measured by neutron attenuation and gravimetrically throughout the growing seasons at each location to compare absolute values and the spatial distribution of soil water with PALMS calculated values. Use of Rosetta calculated soil hydraulic properties improved PALMS soil water calculation from 1-13% of measured soil volumetric water content ('v) depending on soil type. Large-scale models such as PALMS have the potential to more realistically represent management effects on soil water availability in agricultural fields. Improvements in PALMS soil water calculations indicated that the model may be useful to assess long-term implications of management practices designed to conserve irrigation water and maximize the profitability of dryland and irrigated cropping systems in the SHP.