Methods of Growth Analysis in Field-Grown Soya Beans (Glycine max (L.) Merrill)1

Abstract

Investigations on the growth analysis of soya beans (Glycine max (L.) Merrill) involved measurement of shoot and leaf growth by (a), classical equations, and (b) regression procedures. The experiments were carried out at the Western Iowa Experimental Farm, Castana, on Ida Silt loam soil during 1975 and 1976. Soil-water status in the experimental plots was altered by covering the inter-row strips with 4-mM black plastic film and by irrigation in 1976. Relative Growth Rate and Relative Leaf Growth Rate declined with age of the plant because the level of self-shading increased. Net Assimilation Rate and Crop Growth Rate, calculated by using the regression procedure for the uncovered plots, showed a marked increase in the latter part of the growing season due to a combination of decreasing leaf area and increasing dry weights. Classical methods of analysis fail to show this feature because of the non-linear relationship between leaf area and dry weight. It is proposed that in the future more attention should be paid to the use of the appropriate mathematical function describing the changes of leaf area and dry weight with time. Analysis of statistical parameters showed the superiority of using regression procedures.