Yield gap analysis of rice in relation to soil properties in Foumanat plain

Nowadays, due to population growth and changes in eating habits, there is a need to increase agricultural productions to meet consumer demand all around the world. Increasing the area under cultivation is one of the solutions for this problem, which cannot be appropriate in future because this needs to use of marginal lands with low yield and stability. Hence, increased yield is an effective strategy in this regard which can resolve the problem by decreasing yield gap. Considering the fact that there is an urgent need to increase rice production in the country as well as improving the productivity of soil resources, planning for the proper use of chemical fertilizers to achieve the maximum performance seems to be required. Accordingly, the aim of this study was to evaluate rice potential yield and yield gap in Foumanat plain using boundary line analysis, moreover, to find the relationship between soil properties and rice yield.
In order to investigate the yield gap (YG) of rice (cv. ‘Tarom Hashemi’) related to soil properties, a field experiment was carried out in Foumanat plain during two cropping seasons: 2012-13 and 2013-14. We recorded the information of 53 fields as soil samples were taken and geographic coordinates were recorded. Some soil characteristics such as total nitrogen, potassium, phosphorus, organic matter and cation-exchange capacity were measured. At the end of growing season (harvesting time) grain yield was calculated in each field (1 m-2). The boundary line method was used to calculate yield gap, optimum yield and optimum amount of soil properties for each field. Data analysis done by nonlinear regression of quadratic function, dent-like and segmented models based on PROC NLIN procedures.
Segmented functions were well able to describe the trend of pH and electrical conductivity of soil. In addition, dent-like function used to describe the process of changes in available phosphorus, available potassium, organic matter and cation exchange capacity. Also, a quadratic function was used to describe the trend of total nitrogen . The average of optimum yield and actual yield were 7. 67 and 4.81 ton ha-1, respectively, in Foumanat plain with an YG of 2.86 ton ha-1 (37.3 percent). The optimum concentration of total nitrogen, phosphorus, potassium, organic matter, cation exchange capacity, pH and electrical conductivity were 0.266 percent, 13.49-30.35 mg kg-1, 102.2-173.4 mg kg-1, 2.7-3.2 percent, 25.43-30.8 meq 100 g-1, 6.36 and 1.92 dS.m-1 respectively.
Based on the results of this study, some of the main factors for rice YG in this area could be inappropriate management of chemical fertilizer usage (nitrogen, phosphorus and potassium) as well as ignored role of organic matter and cation exchange capacity in providing essential nutrients for rice. Boundary line analysis method could clearly calculate the soil properties potential in response to yield. In general, the results of this study can help to conclude a good strategy for achieving optimal production and gap reduction due to fertility situation of the area.