Light relationships in grass-clover swards

Abstract

Grass-clover swards were grown at four levels of nitrogen to provide a range from extreme clover dominance to extreme grass dominance. Yield, botanical composition, leaf area index, and light density were measured at 3.5 cm vertical intervals in each of the mixed swards throughout the growth period. It was directly demonstrated that the growth of clover in these mixed swards was governed by a series of relationships, namely: (a) Increasing rates of nitrogen application gave increased yields of grass (positive). (b) Increased yields of grass gave higher leaf areas of grass disposed above the clover leaf canopy (positive). (c) Higher leaf areas of grass above the clover reduced the light density at the clover leaf canopy (negative). (d) Reduced light density at the clover leaf canopy caused a reduced growth of the clover (positive). Under conditions of heavy grass growth and of consequent low light density at the clover canopy, the growth of clover not only became slow but eventually was strongly negative, leading to a marked reduction in both the number of clover plants and the yield of clover.