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Effect of Nitrogen and Phosphorus Fertilizers on a Bromegrass and Alfalfa Mixture Grown under Two Systems of Pasture Management. I. Yield, Percentage Legume in Sward, and Soil Tests¹

Bromegrass (Bromus inermis L.) and alfalfa (Medicago media Pers.) herbage production in western Canada can be increased by the application of N and P fertilizers on soils deficient in these elements. This study was conducted to determine optimum pasture production, changes in botanical composition of the sward, and changes in nutrient concentration of Melfort silty clay soil (Typic cryoborolls) from the application of N-P fertilizers on a 4-year-old stand of bromegrass and alfalfa under two pasture management systems. N fertilizer was applied at 0, 45, 90, 135, and 180 kg N/ha each year from 1970 to 1973 in combination with P fertilizer applied to onehalf of each plot at 0 and 20 kg P/ha from 1971 to 1973.

Total yield of bromegrass and alfalfa herbage expressed as a percentage of a control was significantly related to the application of N and P fertilizers and available soil P by regression analyses (R² = 60.4q6). Yields were as high as 251% of controls and ranged from 1,919 to 10,518 kg dry matter per ha. Higher herbage yields were obtained on pastures in which supplementary barlay (Hordeum vulgare L.) was fed to growing animals than on pastures with a "Put and Take" stodtig system. The percentage of alfalfa in the sward was significantly re. duced as much as 29.4% by N-P fertilizers. A higher proportion of alfalfa in the sward was measured under the "Put and Take" treatment (36.9%) than the supplementary barley system (233%). Percentage alfalfa in the sward ranged from 13.8 to 54.8% (1972 to 1973, ranges C and A).

Nitrogen applied at 180 kg N/ha each year to pasture increased nitrate-N in the soil profile to 31.5 µg N/g of soil at the 30 to 60-cm depth. As a result of residual N and P fertilizer, increased herbage yields were obtained 3 years after fertilizer was applied. After this 3-year period, nitrate-N was low, 1.8 µ g N/g soil or less, in the soil profile at all depths.

Nitrogen fertilizer at 90 kg N/ha and P at 20 kg P/ha produced an average increase in herbage yield of 74% or a total yield of 6,129 kg/ha. These rates gave the most economical return on fertilizer invested and did not increase nitrateN in the soil profile significantly.

Key Words: Nitrate-N • Sodium bicarbonate soluble P • Bromis inermis L • Medicago media Pers

² Nuttall, Waddington, and Robertson are research scientists in charge of Soils and Forage and Animal Science Sections, respectively, and Cooke is regional park manager, Melfort, Sask., formerly research scientist in charge of Forage, Research Station, Melfort.

Received for publication January 22, 1979.

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