Abstract
1. Based on the CO_2 balance of photosynthesis and respiration in the forage plant community, we established the equation by which the dry matter production and crop growth rate (CGR) were estimated mathematically. 2. The relation between the amount of dry matter production and CO_2 balance in the plant community can be expressed by the differential equation (1). dw=P(t)・dt-r(t)・W・dt…(1) p(t), change of the amount of photosynthesis a day in the forage plant community ; r(t), change of the plant respiration rate a day ; W, dry matter weight ; t, day 3. It is possible to consider r(t)=r…const., as the change of r(t) in the growth period is relatively low. Namely, eq.(1) is changed into eq.(6). dw=P(t)・dt-r・W・dt…(6) The change of the amount of photosynthesis a day of the forage plant after cutting is approximated with eq.(2) which indicates the saturation curve. P(t)=α(1-e^<-at>)…(2) 4. Solving eq.(6) by substituting eq.(2) into eq.(6), we can obtain eq.(8) by which the change of dry matter weight of forage plant is calculated. Differentiating eq.(8) with respect to t, we can obtain eq.(9) by which the change of crop growth rate (CGR) is calculated.[numerical formula][numerical formula] 5. In the case of P(t)=P…const. and r(t)=r…const., the dry matter weight and CGR in the plant community are calculated by eqs.(10) and (11). respectively. [numerical formula][numerical formula] 6. If these equations are properly used according to the object of studies, we consider that these equations are useful for analyses of dry matter production in forage plant communities.
