Degradation of alfalfa sward
2000
Lillak, R. (Estonian Agricultural Univ., Tartu (Estonia). Grassland Experimental Station)
The investigation based on two field experiments established on loamy Podzoluvisol soil with content of organic matter in 0...20 cm soil layer 2.80...3.20 per cent, available potassium and phosphorus content - 74.3...86.9 and 45.4...50.1 mg/kg, respectively, and pH a sub(KCl) - 6.2...6.4. The changing in quality of alfalfa sward in direction of degradation started at the end of the first wintering when extensive furrows in the roots of alfalfa caused by the larvae's of clover root curculio (Sitona sp.) were possible to observed. These lesions opened a way for infection of pathogens causing root rot and which is progressed year after year. At the same time, depending mostly on the cutting frequency, the number of plants per area unit started consistently decrease. Mortality of alfalfa plants occurred not only during the overwintering period but also during the vegetation period. In the first years of development, compensated by increasing of single plant size, the deterioration of stand density was not resulted by decreasing in yielding ability of alfalfa sward. However, DM-yield started sharply to decrease when the number of plants per square meters to the spring of productive year fall down below 160. Thinning of alfalfa stand and decreasing its productivity allowed the invasion of nonseeded weed species into the sward, which was especially intensive in using 4-cut harvesting system
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