Determination of Critical Level of Soil Phosphorus for Bean

Soil tests play a very important role in management of nutrients in the field. Critical level of soil nutrient elements in a region is the basis of interpretation of the soil test for the same region. Therefore, these tests should be carried out in the soils of the target areas, so that the soil test could be used for fertilizer recommendation. Beans (Phaseolus vulgaris L.) with high protein content are an important crop that is cultivated in Markazi province. Due to the lack of information on phosphorus critical level and regional calibration, this study was conducted on soil under bean cultivation in Markazi province. Twenty-three soil surface samples (0-30 cm) were selected with wide range of soil properties and phosphorus concentration (extracted with Olsen method) from the different locations of the province and were prepared for greenhouse cultivation. Bean plant responses were investigated by application of two levels of phosphorus (0 and 50 mg kg-1 soil as mono calcium phosphate) in greenhouse experiment. The study was conducted in factorial experiment as complete randomized design with three replications. At the end of vegetative period, the aboveground parts of plants were cut, and plant responses including, dry matter weight, phosphorus concentration, total phosphorus uptake, and relative yield were determined. Analysis of variance showed that the main effects and interaction of soil and phosphorus fertilizer were significant at 1% probability level for dry matter weight, phosphorus concentration and phosphorus uptake. The mean comparison of plant responses was significant as affected by phosphorus fertilizer consumption. By using Cate-Nelson graphic method, the critical level of phosphorus in soils was determined to be 13 mg kg-1. Dry matter showed positive significant correlation with available phosphorus and organic carbon. The total phosphorous uptake showed a positive significant correlation with available phosphorous concentration, electrical conductivity, sand and organic carbon content, and a negative significant correlation with clay content.