Quality Changes of Late Summer and Autumn Produced Alfalfa and Red Clover1

Abstract

AbstractLate summer and autumn produced cool‐season grasses have been widely studied as stockpiled forage for pasturage in late autumn and winter. Knowledge of changes in chemical composition and quality of forage legumes during autumn and winter, however, is lacking. The object of this field study was to investigate the quality and chemical composition of late‐summer and autumn produced alfalfa (Medicago sativaL.) and red clover (Trifolium pratenseL.) forage. Samples of alfalfa and red clover grown on a silt loam soil (Typic Paleudalfs) were collected during autumn and early winter of 2 years following cutting at two times in late summer (average dates of 22 August and 8 September). Quality analysis included in vitro dry matter disappearance (IVDMD), N, P, K, Ca, and Mg concentrations in the forage. Nitrogen concentration in red clover forage declined initially after frost and then increased or remained unchanged during the remainder of the sampling period. The decrease in alfalfa N concentration continued throughout the sampling period in 1975 but was similar to the trend for red clover in 1976. The lowest N concentration recorded for either species was equivalent to 17.8 and 17.2% crude protein (CP) for alfalfa and red clover, respectively. In 1975, forage IVDMD declined continuously after frost and reached a minimum of 56.5% for alfalfa and 51.2% for red clover. In 1976, alfalfa IVDMD increased slightly until approximately 30 days after frost and then declined rapidly through 56 days after frost (12 December). The trend of red clover IVDMD in 1976 was similar to that of alfalfa except that the decline in IVDMD began sooner after frost for red clover. In 1976, the lowest IVDMD measured was 68.3 and 58.9% for alfalfa and red clover, respectively. Concentrations of all minerals studied declined during autumn, K being lost most rapidly, P and Mg intermediate, and Ca least rapidly. Averaged over treatments, the loss in K during the sampling period amounted to 77 and 65% of the K present initially compared with losses of 21 and 15% of the Ca during 1975 and 1976, respectively. Results of a 2‐year field study indicate that IVDMD of both alfalfa and red clover declined substantially during late autumn. Nitrogen concentration in the forage, on the other hand, declined initially after frost but then changed little for the remainder of the sampling period. The concentrations of P and Mg in the forage declined to levels below those suggested for several classes of livestock by the end of the sampling period.