Herbage and protein productivity of single or inter-cropped alfalfa and bromegrass under zero nitrogen fertilization
van Kessel, C.
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Nitrogen (N) fertilizer enhances the growth of grass in grass-legume associations and frequently inhibits N2 fixation by the legume-Rhizobium symbiosis. The cost of N fertilizer and environmental concerns related to contamination of groundwater make the use of N fertilizers a less attractive alternative. The herbage and crude protein production of single or inter-cropped alfalfa (Medicago sativa cv. Beaver) and meadow bromegrass (Bromus riparius Rhem. cv. Fleet) grown under irrigation, without N fertilization, were evaluated near Outlook, Saskatchewan, from 1990 to 1992. Hay yield alfalfa increased from 4.5 t ha-1 in the first year to 10.6 t ha-1 in the third year following seeding. The hay yield of bromegrass decreased from 5.3 t ha- in the second year to 1.2 t ha-1 in the following year due to limited availability of N for plant growth. Alfalfa+bromegrass hay yield increased from 4.1 t ha-1 in the first year to 10.5 t ha-1 in the third year. Crude protein yields of single alfalfa or alfalfa+bromegrass were above 750 kg ha-1 year-1 in the first year and increased to 1700 kg ha-1 year-1 in the third year whereas the crude protein yield of bromegrass declined from 300 kg ha-1 in the first year to 80 kg ha-1 in the third year. Crude protein yield bromegrass seeded in alternate rows with alfalfa was up to 25 % higher than that of single bromegrass (not sharing resources). The amount of nitrogen fixation (kg ha-1) on inter-cropped alfalfa in the third year was as high as that of alfalfa not sharing space with bromegrass.
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