Alfalfa yields and quality as influenced by subsurface application of phosphorus, potassium and limestone

Abstract

In a long-term field trial on a Davidson clay loam soil at Piedmont Research Station, Orange, Virginia, in 1979-88, the effectiveness of subsurface (30 cm) placement of P, K and dolomitic limestone on quantitative and qualitative yield, and N fixation capacity of Medicago sativa cv. WL 311 was studied. Single subsurface amendments of 0, 244 or 488 kg P/ha, 465 or 930 kg K/ha and 0 or 22 400 kg lime/ha in 1979 were supplemented by single surface applications of dolomitic limestone in 1980, and annual surface applications of 49 kg P and 186 kg K/ha. M. sativa was sown in 1982 and cut 4 times/year from 1983 to 1988 excluding 1987. Subsurface limestone and P application increased aboveground biomass production in 1986 and 1988 only. Plant N, Ca, Mg and P concentrations were not significantly different. The highest N uptake (246 kg/ha) was obtained with subsurface application of P, K and lime at 488, 465 and 22 400 kg/ha, respectively. Soil pH at ≤15 cm depth averaged 6.9 in 1982-85 and 6.5 in 1988. Subsurface lime application increased soil pH in the plough layer from 6.1 to 7.0; Ca and Mg contents were also increased but Al and Mn soil levels were unaffected. It is concluded that subsurface lime and P fertilizer treatments increased biomass production and nutrient concentrations of M. sativa when no surface lime applications are made and hence the surface soil becomes more acidic. Reduced N fixation appears to be a growth limiting factor for M. sativa grown on acidic soils.