The Relationship Between Shoot Weight, Plant Density and Time During the Propagation of Four Vegetable Species

Lettuce, cauliflower, leeks and celery were grown from seedin a glasshouse at four widely-differing densities on severaloccasions over a 15-month period, under conditions of amplewater and nutrients. For each sowing there were four early harvests.The reciprocal of mean shoot dry weight was found to be linearlyrelated to plant density at any particular harvest as in theShinozaki—Kira equation. The reciprocal of the slope ofthis relationship, representing the ‘ceiling yield m^–2’was roughly proportional to mean daily radiation during theperiod of 14 d before harvest: the reciprocal of the interceptwas logarithmically related to accumulated heat units, modifiedfor daily radiation. Hence mean plant weight could be expressedas the following function of environmental variables and plantdensity: w^–2 = w₀^–pe^–p.