Balances of the major nutrients N, P and K at the farm and field level and some possibilities to improve comparisons between actual and estimated crop yields

Since 1994 Lithuania is engaged in BEAROP-the international study of agriculturally derived runoff of nutrients from the countries round the Baltic Sea, proposed by Swedish scientists. One of the demonstration watersheds chosen for this project, river Graisupis watershed, is located in the agricultural plains region of Middle Lithuania. Crop yield and nutrient balance data obtained for V. Liutkevicius Demonstration farm at the scale of farm and field are discussed. It was evident after calculations of the flow and balance of N, P and K to observe a discrepancy between actual and estimated values of crop yield. This is a common problem in Lithuania where an unbalanced fertilisation system still exists on many farms, when farmers choose the fertiliser rates, too little attention is paid to the soil analysis and soil nutrient balance. In order to make the fertilisation system more rational, a balanced fertilisation computer model was created at Lithuanian Institute of Agriculture (LIA) and used for that purpose at the Demonstration farm. A drained system of 7.4 ha divided into separate fields, growing a mixture of ley at the Demonstration farm was chosen for the nutrient balance calculation in 1997 and 1998. Calculations of major nutrient flows at the field level have shown that the N balance in this field was positive and P almost in balance, however, the potassium balance was negative. It may be rational to utilise such a local organic fertiliser as urine in this field. The regression equation was developed that relates N surplus with nitrate loss and could be used more widely provided data were available on drainage discharge, total N content in soil, humus content, fertilisation rate. Soil testing at the Demonstration farm should be extended to the areas examined more than 10 years ago. More attention has to be given to the integrated plant protection and soil cultivation measures in order to obtain the planned yields. (C) 2003 Elsevier B.V. All rights reserved.