Alfalfa fertilization
Alfalfa is a major consumer of nutrients
Nitrogen is provided mostly symbiotically from soil reserves, but for high and constant yields, especially in dry regions, it is recommended to apply low doses of nitrogen (N30-35) at the beginning of spring. On soils with low content of humus (<2%) and nitrogen, nitrogen doses needed may be higher (N40-60), applied in early spring or fractionally, after the first harvests.
Fertilization of alfalfa with nitrogen fertilizers did not prove economically efficient when it was grown in pure culture, but when it was grown in mixtures with perennial grasses, especially on soils whose humus content was less than 2.2-2.5%, a moderate dose of nitrogen fertilizer proved to be economically effective.
Phosphorus and potassium are applied depending on the soil content in these elements. For alfalfa, the optimal soil content in phosphorus is 8-10 mg / 100 g soil, and in potassium, 18-22 mg / 100 g soil (I. Moga, 1973; C. Bărbulescu et al., 1991; I Moga et al., 1996).
Phosphorus has an important role in the assimilation of nitrogen, the synthesis of proteins and carbohydrates. The normal supply of phosphorus soil at the establishment of the alfalfa culture determines a good development of the root system.
The effect of phosphorus deficiency during this period cannot be compensated in the following years. Phosphorus fertilizers, in doses of 30-120 kg / ha (higher doses in irrigated conditions and on acidic soils), are applied when doing soil tillage and then every 2-3 years.
Potassium has an important role in increasing the resistance of plants to drought, by reducing perspiration. In general, the soils of our country are well supplied with potassium, except for the acidic ones. Potassium fertilizers are applied in the same way as phosphorus fertilizers.
Manure is well exploited by alfalfa on all types of soil, but especially on acidic and irrigated land. In the case of alfalfa, manure is used optimally when it is administered to annual fodder crops, the alfalfa rotating in the third year after administration. Manure can be applied to the preceding plant or directly to the alfalfa crop, under the basic plowing. During crop use, well-fermented manure is applied to the soil surface during the cold season. When manure is used, nitrogen and potassium fertilizers are given up, and those with phosphorus are reduced by up to 50-60%. The most effective doses are 35-40 t / ha for non-irrigated soil and 60-80 t / ha for irrigated soil.
An important role in the nutrition of alfalfa plants is also played by microelements, especially molybdenum, boron, sulfur and cobalt, which stimulate the process of fixing nitrogen in a symbiotic way, iron, manganese and zinc, as a catalyst in the process of photosynthesis.
The most economical and complete source of soil supply with microelements is manure.
The application of calcium amendments is recommended on acid soils, with pH (H2O) <6.2 and the degree of base saturation (V%) <80%.
The amendments are incorporated under the basic plowing, together with the manure and the fertilizers with phosphorus and potassium, after having previously been well crushed, evenly dispersed and homogenized with the superficial layer of the soil, through 1-2 passes with the disc harrow.