ABSTRACT
Phosphorus, potassium and sulphur application on alfalfa

Hernán Acuña P.1, Patricio Soto O.1, Agustín Vidal V.2y Germán Martínez R.1
 
Phosphorus, potassium and sulphur were applied on a lucerna sward, cv. Huinca, grown in volcanic soilon Humán series (Typic distrandept). The treatments (21) were selected from all combinations of fourrates of P (0, 33, 66 and 132 kg/ha per year), tour rates of K (0, 42, 84 and 168 kg/ha per year), and fourrates of S (0, 30, 60 and 120 kg/ha per year). The experiment was conducted during four growingseasons (1985/86 to 1988/89). A randomized block design, with four replications, and 2.5 x 4 m plots wasused. Dry matter (D.M) production was measured by cutting, four to five times per growing season. Thetotal herbage harvested was analized to determine N, P, K, Ca and Mg uptake. Extractable P and K in soilat 0 - 10 cm depth was measured before, in the meantime and at the end of the experimental period.Extractable P at different layers, up to 80 cm depth, was measured after the last cut in 1989.
Annual D.M. yield increased by 10%, as average of the four growing seasons (16.9 to 18.71/ha with 0 and132 kg/ha of P, respectively). The response was constant between 0 and 132 kg/ha of P and reached 18 kg of D.M. per kg of P aplied, in 1987/88. The response of K was also low and it was present since the thirdgrowing season. Dry matter production was not affected by S aplication. The extractable P in soil (0 - 10cmdepth) tended to decrease, between 1986 and 1989, in the plots without P application; but, when 132 kg/ha per year of P were applied the extractable P reached 29 and 37 ppm in the 0-10 and 0-5 cm layers,respectively. Extractable K in soil decreased from around 150 ppm, in 1986, to 26, in 1989, when 66 or 132kg/ha of P was applied, or when K rates were 84 or less kg/ha per year. The N yield and the P, K Ca andMg uptake are discussed.
Key words: alfalfa; lucerne; P, K and S applications; nitrogen yield; P, K, Ca, Mg uptake
1Estación Experimental Quilamapu (INIA), Casilla 426, Chillán, Chile.
2Subestación Experiemental Humán (INIA), Casilla 287, Los Angeles, Chile.