Net photosynthesis
The crop plants need to perform at optimal level not only with respect to capturing light in crop canopy, but to efficiently utilize it for greater dry matter yield. The higher rate of photosynthesis (Pn) per unit leaf area, therefore becomes important. In most crop species, however, there has been little change in the rate of leaf photosynthesis per unit area to accompany the substantial genetic increase in grain yield. Most often, photosynthesis yield relationships are considered in terms of single leaf photosynthesis. Photosynthesis measurements of a few minutes duration using defined leaf position at radiation saturation may not be assumed to represent the productive potential of the crop. Leaf photosynthesis rate varies with leaf age, position, time of the day and sink strength44–47. An inverse relationship between leaf size and photosynthesis rate has been observed48–50. It was