YIELD AND NUTRIENT USE EFFICIENCY OF FIELD CROPS GROWN IN THE REGION OF SADIEVO, SOUTH BULGARIA

Fertilizer experiment in four field's crop rotation (wheat, barley, maize, and sanflower) was carried out in the region of Sadievo, Bulgaria, during the period 2009-2012. The aim of the research was to study the effect of fertilization on crop productivity and nutrient use efficiency (NUE) of the mentioned four field crops. The fertilizer treatments were: Control N; P; K; NP; NK; PK: NPK. Agronomic Efficiency (AE), Partial nutrient balance (PNB) and Recovery efficiency WE) were the indicators calculated for assessing the NUE. The fertilization was very effective practice NPK treatment ensured 71% higher yields for maize, 64% for wheat, 60% for barley and 51% for sunflower in comparison with control, on average for 4 years period. In spite of the relatively good fertilization effect, AE data was lower than reported as typical levels for cereals crops which showed relatively low productivity of unit nutrient input. PNB values for K showed that removed nitrogen amounts were higher and the deficit was less pronounced in wheat. In maize and sunflower PNB value for N were high and showed a severe nitrogen balance deficit PNB and RE values for P showed that the fertilization rates could he decreased, while PNB and RE for K indicated that for maintaining the soil K content, the fertilization with K was recommendable in spite of the relatively low agronomic efficiency.