Investigating the Effect of Soil Properties on Yield and Modifying the Crop Requirements Table of Maize

Maize has special importance among cereals across the world, because it has many industrial applications in addition to food consumption. However, the production of this crop requires high amounts of water and fertilizers. The number of inputs will be increased in case of the limited lands are available for cultivation of this plant. Accordingly, land suitability for maize should be determined in order to find the best suitability classes for selection of lands with lower land limitations. The objective of this study was to investigate the effects of soil properties on grain yield of maize in order to determine different soil rating for suitability classes of Maize.

To achieve the objectives of this study, a total of 101 grain maize farms in Khuzestan, Kerman, Fars and Qazvin provinces were selected. A questionnaire form was completed for each farm. A soil pedon was also studied and some soil samples were taken to accomplish the related physicochemical analyses. After that, multivariate regression was performed simultaneously between yield as a dependent variable and different soil properties as independent variables. Subsequently, in order to modify an earlier version of soil and landscape requirement table, the simple regression analysis were performed to find the relationships between soil properties and maize yield for modyfing the rating classes of different land suitability classes. The available soil and landscape table for maize is based on a review of literature and experts opinion. Therefore, it was modified based on the collected data as well as the actual maize yield of farms in different regions of Iran. The verification of the proposed table was performed using data from 14 maize farms (about 14% of data) which was not used in the preparing the table. In the random selection of these 14 points, two samples from Fars, three samples from Qazvin, five samples from Kerman and four samples from Khuzestan were included.

Results indicated that the range of yield variation, lime, sand, clay, silt, exchangeable sodium percentage and soil salinity are high, but the percentage of organic carbon, soil pH and gravel percentage are distributed in a small range. In multivariate regression, the variables of salinity, exchangeable sodium percentage, sand percentage, organic carbon, soil pH, lime and gypsum contents were included, respectively. The coefficient of determination of the proposed relationship was about 0.83. Therefore, the variables entered in the model were able to explain about 83% of variance of the changes related to dependent variable. By using this equation, some simple soil properties can be used to estimate the maize yield. Using simple regression equations, the effect of each soil characteristic on yield was determined and with their help, the soil and landscape requirement table of maize was modified. The value of coefficient of determination between yield and soil index for the verification data was about 0.86, which indicates the reliability of the table proposed in this study. Comparison of this table with the proposed soil and landscape requirements table for maize presented by Sys et al. (1993) indicated that there are many differences in the boundaries of proportion classes for lime and gypsum variables. There is also a difference in the salinity and sodicity variability of the soil at the boundaries of classes S2, S3 and N.

Overall results of this study indicate that the main land limiting characteristics for maize production in the studied regions are soil salinity and sodicity. After these two variables, organic matter and soil pH are the main and effective factors influencing grain maize yield in selected farms across the country. In some areas, such as Kerman and Qazvin provinces, the physical properties of soil are limiting for maize cultivation and thus adversely affect reduction of the yield. As a consequence, it is clear that before planting any crop, the land suitability evaluation for any crop must first be assessed. By using the crop requirements table of each crop and land suitability evaluation one can recognize the land imitations of each region for cultivating that crop. Then, according to the type of limitationt, special management can be assigned for each region.