Forage Nutritive Value as Affected by Fertilizer Application

SUMI~IARYThe digestibility of orchardgrass was determined as affected by fertilizer application.Results showed that under favorable conditions, digestibility, as well as dry matter and energy yields of forage, can be significantly increased by the use of fertilizer.Under unfavorable conditions, few or negative digestibility effects were noted.Increasing plant pigment content was found to be associated with higher forage digestibilities.Under favorable conditions, fertilizer treatment raised the pigment content of forage.Under favorable growth conditions, aftermath forage harvested on the same date but given dissimilar fertilizer treatment was found to differ in digestibility and feeding value.Digestibility data showed divergence among the digestibility methods used.Not only did each of the three pigment methods differ significantly from the standard total collection method but they also d~ered significantly from each other.The variable response of forage crops to fertilizer applications has been studied extensively.Ward (10) has recently and adequately reviewed this subject.I-Ie concluded that the divergent results frequently ascribed to fertilization were due to several factors, such as soil types, relative level of soil fertility, ratios of available nutrients, plant species, and climatic conditions such as temperature, precipitation, humidity, and wind velocity.In addition, iY[arkley et al. (4), using 200 lb. of nitrogen per acre, reported a significant increase in the apparent digestion coefficients of protein and TDN of bromegrass and orchardgrass rations over those of low-N rations.The objectives of this experiment were to investigate the response of forage digestibility to fertilizer treatment, and to study the effect of fertilizer on plant pigment concentration and its relationship to forage digestibility when determined by both standard and pigment methods. ]EXPERIlYiENTAL PROCEDURETrial 1.After the first cutting had been removed, a section of an orchardgrass field was treated with 100 lb.ammonium nitrate per acre.No fertilizer was applied to the remaining portion of the field.During early growth the fertilized grass was taller and greener than the unfertilized forage.However, a severe drought (0.29 in. of rainfall in 17 days, accompanied by a hot, dry wind) occurred, which caused the color difference between the grasses to disappear, and the plants to become dry and withered.At the time of the digestion trial the entire field had a greenish-brown color.