Fertilizer Response of Irrigated Alfalfa in Southern Alberta

Fertilizer Response of Irrigated Alfalfa in Southern Alberta

R.C. McKenzie^l, S.A. Woods^l, R.H. McKenzie² and L. Kryzanowski³
^lSoil & Water Agronomy Unit, Crop Diversification Center - South,
Alberta Agriculture Food and Rural Development (AAFRD), Brooks,
AB, Canada, ²AAERD, Lethbridge, AB, ³AAFRD, Edmonton, AB

Alfalfa is an important crop in the irrigated areas of Southern Alberta, however, it frequently receives lower inputs of fertilizers than other crops. A survey of 99 irrigated alfalfa fields was conducted in southern Alberta. Soil phosphorus (P) was found to be low in 70% of the alfalfa fields and marginal on 11% of the fields, but plant tissue P was found to be deficient in only 43% of the fields. Soil potassium (K) was found to be marginal on 12% and adequate on 88% of the alfalfa fields but tissue K was deficient on 79% of the fields. Soil nitrogen (N) was low on 96% of the fields sampled and marginal on 2% of the fields yet tissue N was low on only 1% of the fields. To address the questions that arose from the conflicting results of this survey, a field experiment was conducted to measure the increases in forage yield to various rates and methods of application of P, K and N fertilizers. Phosphorus responses could be best predicted by a combination of soil and tissue tests. On high pH soils, the Kelowna method of determination of soil P was more reliable than the Miller-Axley method in producing a P deficiency. Shallow banded P was equally effective as broadcast P. Annual applications of P over 3 years gave similar yields to one batch application. Soils with marginal or adequate levels of K produced alfalfa with deficient levels of tissue K. These same soils did not give a significant increase in forage yield with K fertilizers. Nitrogen fertilizers increased the forage yield in the first harvest after application. It was not measured how much of this increase was due to increased growth of weeds. Tissue nutrient levels in Alberta fields differed considerably from sufficiency levels developed in the USA. This suggests a need for refining these standards for the local conditions, which include high pH soils, short growing season and cool night temperatures.

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