The effect of tillage and crop rotation on the content of available nitrogen, phosphorus and potassium
¹Department of Field Crop Husbandry, Estonian Agricultural University, Kreutzwaldi 64, 1008 Tartu, Estonia; e-mail: firstname.lastname@example.org
²Department of Soil Science and Agrochemistry, Estonian Agricultural University, Kreutzwaldi 64, 1008 Tartu, Estonia; e-mail: email@example.com
This research (A long-term field experiment from 1982 to 1997) was conducted at the experimental station of the Department of Field Crop Husbandry of the Estonian Agricultural University. The soil of the experimental site is moderately moist slightly podzolised sandy clay.
Insofar as field crop husbandry is concerned the soil should contain optimal amounts of available nutrients. If the level of available nutrients in the soil is low the plants will suffer and the yield will be low. A rise in soil available nutrient content leads to increased yield of crops, but only up to a certain level (optimal content). Thereafter, a further rise in soil nutrient content fails to effect any significant increase in the harvest.
The soils of the Eerika trial plot have optimal nutrient content and little need for fertilisation. After two crop rotations significant changes in nutrient content and location were observed in the ploughed layer. Compared to the nutrient content determined at the start of the trial period (1982), the greatest changes occurred in the soils under a crop rotation involving cereals, potato and a mixture of red clover and timothy, in which the supply of available phosphorus decreased by 19 mg kg-1 and that of potassium by 121 mg kg-1 on average after two rotations. Compared to the cereal rotation and the rotation containing 50% of cereals and 50% of potato the available phosphorus content dropped by 12–33% and the potassium content by 41–46% in the upper 25-cm soil layer.