FOOD RESERVES IN RELATION TO OTHER FACTORS LIMITING THE GROWTH OF GRASSES

Abstract

Marked quantitative responses of root, rhizome and top growth of grasses (blue grass, red top, fescue and timothy) grown under field and greenhouse conditions are correlated with cutting treatments which affect the internal environment. Not only did the amount of subterranean growth and total weight of top growth, ultimately, tend to vary inversely with the frequency of defoliation but reduced growth sometimes occurred for several months subsequent to excessive defoliations. It is clearly evident that the productive capacity of grasses is not only dependent upon adequate supplies of available nutrients and moisture combined with favorable light and temp. conditions but also upon the food reserves of the plant. When photosynthesis is interrupted by frequent removals of top growth the limitations of subterranean development may involve greater susceptibility to drought, lessened absorptive capacity and increased winter and insect injury. Frequent and close removals of the succulent top growth of grasses having abundant reserves make a heavy draft on the supplies of available nitrogen in the soil so that the first important factor of growth limitation may be nitrogen deficiency. When an abundant growth of blue grass occurs with fertilization and delayed cutting the recovery after such cutting is often slow and uneven due, in part, to etiolation and the death of many basal leaves occasioned by the dense growth above. Such delay in recovery may, under favorable climatic conditions, encourage the ingress of certain weeds and may prove significant in the management of heavily fertilized pastures or of turfs and lawns where uniformity is desired. Organic food reserves have a significant ecological relationship, especially with reference to the flora of grasslands. Aside from the occurrence of weeds with delayed cutting, the maximum competitive efficiency of beneficial grasses, as measured by invasions of other plants among them, occurred generally, when optimum fertility was combined with those practices of cutting or grazing which maintained a productive level of reserve foods in such grasses.