Vegetative Growth of Corn as Affected by Population Density. II. Components of Growth, Net Assimilation Rate and Leaf‐Area Index 1

THE complex problem of accounting for variations in the growth of crops may be simplified by consideration of two components of growth in a plant community, the net assimilation rate and the leaf-area index. The net assimilation rate (or "unit leaf rate" of some authors) as conventionally expressed is a measure of the net gain of dry matter of a community of plants relative to their leaf area, and is usually regarded as an indicator of mean photosynthetic efficiency (9). Since the rates measured are "net" assimilation rates both photosynthesis and respiration are taken into account. The use of the leaf area as the term of reference is somewhat arbitrary as other plant organs often participate in photosynthesis, and indeed, all living plant organs respire. However, it is convenient to use leaf area as a consequence of it being usually the main photosynthetic organ. Net-assimilation-rate calculations customarily have been based on a linear relationship and occasionally on a quadratic relationship between crop-dry-matter production (W) and leaf-area index (L). Recently Whitehead and Myerscough (11) have used the exponential relationship, W = kL" + c