Using boundary line analysis in yield gap studies: Case study of wheat in Gorgan

Background and objectives:
Due to increase in the world population and increasing concerns about the future food security, shrinking the yield gap has became a hot area of research in field crops. Estimation the amount of yield gap and determination of it’s causes requires using proper methods. Boundary line analysis is a statistical method that can quantify the response of yield to an environmental or management factor in a situation in which other parameters are variable. Indeed, this method is able to determine the response of yield to a desired factor while other factors are appropriate.The first objective of this study was to introduce a method of boundary line analysis as a practical analysis in yield gap studies of crops. Another one was how to use of this method to determine the best managements and estimate the potential yield and yield gap of wheat in Gorgan.

Materials and methods:
With sampling of farms and use of this method, we can determine potential yield and the reasons of yield gap and also the importance of each parameter in the yield gap. In this study, we explain how to use this method using the data of 95 wheat farm collected in 2008 and 2009 in Gorgan. Management factors include the amount of nitrogen fertilizer (N) (at the base and road), phosphorus (P2O5), potash (K2O), frequency of irrigation, plant density and planting date.

Results:
The results show that while the average yield of farmers is 4700 kg, they can achieve up to 6200 kg ha-1 by improving their agricultural management. For this purpose, the following should be considered: (1) using at least 96 kg of N fertilizer in which 73 kg of it should be used in split application, (2) using at least 31 kg of P2O5 and 40 kg of K2O as a base fertilizer, (3) at least two irrigations, (4) plant density of 182 to 447 in m2, and (5) planting date before the late of November.

Conclusion:
Boundary line analysis in yield gap studies could clearly show the responses of yield to management factors and estimate possible yield potential. Interpretation of the analysis’s results is very simple and clear. In addition, it seems that this analysis reduce the need to common experiments and also have provided good clues to design new field experiments. With a good sampling of farms in several years and use the ability of such methods we can find the ways of increasing production. It is strongly recommended that the boundary line analysis use as a practical analysis in yield gap studies of crops