Effect of mineral fertilisation on the yield and quality of pea (Pisum sativum L.)

The effect of various N, P and K supply levels and their combinations on the development, weed infestation and yield of the pea variety Ujmajori and on the available macro- and microelement contents of the ploughed layer was investigated in the 17(th) year of a long-term mineral fertilisation experiment on loamy chemozem soil with lime deposits. The soil of the growing site contained 3% humus, 5% CaCO3 and 20% clay in the ploughed layer, and was classified as poorly supplied with P and Zn and moderately well with N and K. The experiment was set up with 4N x 4P x 4K = 64 treatments in 2 replications, giving a total of 128 plots. The mineral fertilisers were applied in the form of calcium ammonium nitrate containing 25 % N, 18 % superphosphate and 50 % potassium chloride. The groundwater was at a depth of 15 m and the area was prone to drought. The main results were as follows: 1. After fertilisation with superphosphate, not only was there an increase in the available P content in the ploughed layer as determined by various methods (ammonium lactate, NaHCO3, NH4-acetate + EDTA), but the available Sr reserves almost doubled, since the Sr contamination of the superphosphates applied was as high as 1-2 %. K fertilisation increased the available supplies of K, Mg, Na, Al, Fe, Ba and Ni, while reducing that of Zn. The composition of the 50% potassium chloride only provides an explanation for the accumulation of Na and Mg in the topsoil. 2. The effect of N fertilisation was reflected in the increased NO3-N concentrations and in die reduced reserves of available K. The latter may be related to the higher yield averages achieved on N-fertilised plots, and to the large quantities of K removed from these plots in the course of 17 years. 3. At N rates in excess of 100 kg . ha(-1) . year(-1) the stand became thinner and weed-infested, while there was a reduction in the stem, pod and seed yields. Overfertilisation with P and K did not lead to yield depression. In the early stages of development the P effect was dominant, while during ripening N and K effects were dominant. The optimum supply levels on this soil amounted to 0-100 kg . ha(-1) . year(-1) N, 120-130 mg . kg(-1) AL-P2O5 and 180-190 mg . kg(-1) AL-K2O. 4. The crude protein content in the seed yield was 23 % in the N control and 30 % at the maximum N rate. With the exception of arginine there was a reduction in the quantity of amino acids as the result of N effects. This reduction amounted to a total of 5% for both the essential and the non-essential amino acids. Amino acids made up 97% of the seed protein on N-deficient soil and 87 % on soil with excessive N supplies. The P treatments gave no significant modification in the amino acid composition of the seed protein. 5. In animal feeding experiments the body mass increase of young rats increased by 2-3 times when they were fed pea seeds rich in P, while their net protein utilisation (NPU) also improved by 10-15% compared with the P control. N fertilisation had the opposite effect.