Recently more extensive investigations were undertaken, designed to study the effect of various amounts of mineral and organic fertilizers on yield and nutrition regime.
Two experiments were carried out, the first using various rates of mineral fertilizers, and the second organic fertilizers.
The experiment with application of various rates of mineral fertilizers is conducted since 1966, the following amounts in active substance being applied per decare (one decare =0.10 ha):
1) NoPoKo - control; 2) N30P15K60; 3)N30P30K60; 4) N30P45K60;
5) N30P30K30; 6) N30P30K90; 7)N45P30K60; 8) N45P45K90;
Ten tons/decare barn yard manure were applied in all variants, inclusive of the control, during each of the first two years.
The quantity of barn yard manure was reduced to 5 t/decare in the following years with a view to obtaining more distinct results from the mineral fertilizers since the soil was well supplied with nutrients.
The experiment was conducted after the block method in six replications, the size of the field plot being 9.6 sq. m.
The barn yard manure is applied as basal dressing about a month prior to planting the crop.
Two thirds of the superphosphate and one half of the potassium sulphate are introduced with it.
The remaining amounts of these fertilizers and the ammonium nitrate are applied during the growing season in 9 top-dressings carried out depending on the developmental phases of the plants.
Planting takes place in late September.
Annual agrochemical analyses were made prior to basal dressing during three definite phases of plant development and following termination of harvesting in order to establish the soil content of nutrient elements.
Prior to basal dressing and at the end of the growing season the soil samples were taken from the 0–20 cm and 0–40 cm layers, and the rest only from the 0–20 cm layer.
The analyses were made after the following methods: total nitrogen - after Kjeldahl, ammonium and nitrate nitrogen - by distillation, total P2O5 - with perchloric acid, mobile P2O5 - after Egner-Rhiem, mobile K2O - after Egner-Rhiem and with ZnHCl, organic matter - after Turin, pH - potentiometrically.
The experiment is carried out on leached meadow cinnamonic soil with antropogenic influence and relatively light mechanical composition, good mechanical and physical properties, good aeration and water