Path Analysis of Factors LimitingCrop Yield in Rice Paddy and Upland Corn Fields

Knowledge of the relationship between crop yield and yield limiting factors is essential for precision farming. However, developing this knowledge is not easy because these yield limiting factors are interrelated and affect crop yield in different ways. Data for grain yield and yield limiting factors, including crop chlorophyll content, soil chemical properties, and topography were collected for a small (0.3 ha) rice paddy field in Korea and a large (36 ha) upland corn field in the USA, and relationships were investigated with path analysis. Using this approach, the effects of limiting factors on crop yield could be separated into direct effects and indirect effects acting through other factors. Path analysis provided more insight into these complex relationships than did simple correlation or multiple linear regression analysis. Results of correlation analysis for the rice paddy field showed that EC, Ca, and SiO2 had significant correlations with rice yield, while Ca, Mg, Na, SiO2, and P2O5 had significant correlations with the SPAD chlorophyll reading. Path analysis provided additional information about the importance and contribution paths of soil variables to rice yield and growth. Ca had the highest direct effect (0.52) and indirect effect via Mg ( 0.37) on rice yield. The indirect effect of Mg through Ca (0.51) was higher than the direct effect ( 0.38). Path analysis also enabled more appropriate selection of important factors limiting crop yield by considering cause and effect relationships among predictor and response variables. For example, although pH showed a positive correlation (r=0.35) with SPAD readings, the correlation was mainly due to the indirect positive effects acting through Mg and SiO2, while pH not only showed negative direct effects, but also negatively impacted indirect effects of other variables on SPAD readings. For the large upland Missouri corn field, two topographic factors, elevation and slope, had significant direct effects (P<0.1) on yield and highly significant correlations (P<0.01) with other limiting factors. Based on the correlation analysis alone, P and K were determined to be nutrients that would increase corn yield for this field. With the help of path analysis, however, increases in Mg could also be expected to increase corn yield in this case. In general, path analysis results were consistent with published optimum ranges of nutrients for rice and corn production. We conclude that path analysis can be a useful tool to investigate interrelationships between crop yield and yield limiting factors on a site specific basis.