Wetting and Maturity Effects on Mineral Concentrations in Legume Hay1

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Abstract
Wetting by rainfall during field drying of legume hay reduces forage yield and in vitro dry matter disappearance. Field experiments were conducted to evaluate wetting effects on mineral composition of alfalfa (Medicago sativaL.) and red clover (Trifolium pratenseL.) hay. Three and one‐half kg samples of each species, grown on Plano silt loam soil (fine silty, mixed, mesic Typic Argiudolls) and harvested at early and late maturity stages, were placed on wire screens and allowed to dry without wetting or were exposed to natural or artificial wetting in 1980 and 1981. A completely random design was used with three replicates in 1980 and two in 1981. In 1980, 25 mm of water was applied using sprinklers to hay wetted during drying. In 1981, hays wetted during and after drying were exposed to 41 and 62 mm of natural precipitation, respectively. Late maturity (fullto late‐bloom) forage was lower in P, K, Ca, Mg, and S than early maturity forage (early bud to first flower) of the same species. Artificially wetted and well cured hay did not differ significantly in concentrations of P, K, Ca, Mg, or S in 1980. Precipitation totaling 62 mm on dry early to late‐bud alfalfa hay reduced the K concentration from 28.1 to 15.5 g kg−1, indicating substantial leaching. The same treatment increased P concentration from 4.1 to 5.5 g kg−1, increased Ca from 13.0 to 19.7 g kg−1, and increased Mg from 4.2 to 5.0 g kg−1. Late‐bud and first‐flower red clover responded similarly when subjected to the same treatment. Late‐bloom alfalfa, exposed to 41 mm of precipitation during drying had 2.4 g kg−1of P, 15.9 g kg−1of K, 8.2 g kg−1of Ca, 1.9 g kg−1of Mg, and 1.6 g kg−1of S compared with 2.5,20.8, 11.5,2.5, and 2.2 g kg−1, respectively, for the same minerals in hay cured without wetting. Based on these data, the impact of wetting during hay curing on concentrations of P, Ca, Mg, and S was smaller than wetting effects on forage yield and in vitro dry matter disappearance. Wetting reduced K concentration to a greater extent than it reduced the other minerals studied. Alfalfa forage was consistently higher in S and lower in Mg than red clover forage of similar maturity.