Alfalfa Response to P and K Fertilization

The CSP (concentrated superphosphate) in this experiment appeared to be superior to PARP (partially acidulated rock phosphate) for alfalfa production. The chemical composition of the plant was affected by P and K treatments. Application of CSP alone, rather than with K₂SO₄ appeared to increase the N content. The P content of the tissue was generally lower on the check plots; highest where CSP was applied alone, with the other two treatments falling in between and being similar to each other. The K content of the tissues was highest where K₂SO₂ was applied, followed by the check plot. Because of increased yields, as compared with the check plot, the K content was lowest where either PARP or CSP was applied alone with no significant difference between these two sources. The S content in 1970 was significantly increased when K₂SO₄ was applied with the CSP as compared to where CSP was applied alone. Lower sulphur content where either PARP or CSP was applied alone, may by attributed to higher yields as compared with the check plots. The application of K₂SO₄ in 1971, significantly increased the S content of the alfalfa as compared with that on the check or PARP plots.

The available phosphorus in the soil was significantly higher where P was applied. Plots receiving CSP plus K₂SO₄ contained a significantly smaller amount of available P than plots receiving PARP. Plots receiving K₂SO₄, contained significantly higher amounts of available K than plots not receiving K. No significant differences were observed in the available Ca and Mg contents. However, the Mg content was lowest where CSP was applied with K₂SO₄.

From an economic standpoint, PARP was found to be well comparable to CSP, per dollar returns being δ 4.15 and 4.18 respectively.