THE RESPONSE OF A GRASS-LEGUME SWARD TO POULTRY MANURE
Poultry numbers, density and potential environmental quality problems have increased greatly in the Lower Fraser Valley. A field experiment was carried out in 1975 and 1976 to determine the effect of manure from a deep-pit laying house on the growth, yield and chemical composition of orchardgrass-ladino clover forage. The manure had N:P:K, ratios of 5.1:2.5:2.0 and 3.5:1.6:1.4 in 1975 and 1976, indicating that its K content relative to N and P was relatively low for forages. Manure rates were 1.25, 2.5, 5.0, 10, 20 and 40 t/ha. In 1976, these rates were applied as a single application in the early spring or split into three equal increments applied in the early spring and following the first and second cuts. The grass component of the sward responded positively to increased manure rates. However, at rates in excess of 2.5 t/ha, the clover was almost totally eliminated from the stand. The maximum 1975 dry matter yield of 7.00 t/ha occurred with 40 t/ha of manure although the rate of yield increase was greatest at rates of 10 t/ha or less. The maximum forage yield of 16.1 t/ha occurred in 1976 at the 20 t/ha split-application rate of manure. At the 5, 10 and 20 t/ha manure rates the split application produced yields about 1.2 t/ha higher than the single application method. Except for the last cuts in both years, manure significantly increased percent total Kjeldahl nitrogen, especially at rates of 20 t/ha or less. Forage NO3-N concentrations exceeded 0.20%, the level cited as being toxic to ruminants, at rates of 20 and 40 t/ha. Forage P concentrations were not significantly affected by manure addition, probably because the available P level in the soil was high. Forage K concentrations were increased at all cuts by increasing manure rates although K was not a factor in the crop response to manure because initial soil K was high. Manure applied at rates in excess of 20t/ha to supply adequate K for forage production would make inefficient use of the N and P in the manure. Good forage yields without damage to the sward and with little problem with high forage NO3 concentrations were obtained at the 10 t/ha rate; however, for manure disposal, rates as high as 20 t/ha could be used.