Nutrient uptake of potato (Solanum tuberosum L.) on calcareous chernozem soil

The effect of different levels of N, P and K supplies (poor, medium, satisf actory, excessive) and their combinations was investigated on the mineral c omposition, nutrient uptake and specific element contents of potato (variet y Desire) grown on calcareous loamy chernozem soil. A further aim was to ch eck the concentration limits used by the extension service for leaf diagnos is. The ploughed layer contained 5% CaCO3, 3% humus and 20-25 % clay, and h ad a pH of 7.3 pH((KCl)). Soil analysis showed the original soil to be poor ly supplied with P and Zn and moderately well supplied with N and K. The mi neral fertilisation experiment involved 4Nx4Px4K = 64 treatments, or nutrit ional situations, in two replications, giving a total of 128 plots. The N l evels were 0, 100, 200 and 300 kg/ha/year N, and the PK levels were 0, 500, 1000 and 1500 kg/ha/10 years P2O5 and K2O, applied in the form of calcium ammonium nitrate, superphosphate and 50% potassium chloride. Replenishment fertilisation with P and K was carried out when the experiment was set up i n autumn 1973. The plot size was 6 x 6 = 36 m(2) and the forecrop was 2 yea rs of maize. The groundwater depth was 15 m. The main conclusions were as f ollows: 1. On this relatively humus-rich loamy soil, satisfactory N levels for pota to can be characterised by values of 4.5-5.0% N at the beginning of floweri ng, 3.5-4.0% at the end of flowering and 1.5-2.0% prior to harvesting in ai r-dry leaves, or 1.7-1.8% N in the tubers. Satisfactory values of P are 0.4 0-0.50% at the beginning of flowering, 0.25-0.30% at the end of flowering a nd 0.1-0.15% at harvest in the dry leaves, or 0.25-0.30% in the dry tubers. Satisfactory K supplies were reflected by K concentrations of 3.0-4.0% at the beginning of flowering, 2.0-3.0% at the end of flowering and 1.0-1.5 % at harvest in dry leaves, or 1.5-2.0% in the tubers. These data can be used as guidelines by the extension service. 2. The ratio of the major elements also gives a good reflection of the nutr itional status of the plant and can thus be used for diagnostic purposes. T he data suggest that the satisfactory or "normal" N/P ratio in the dry leav es is 10-12 at the beginning of flowering, and 12-15 at the end of flowerin g and at harvest. The K/P ratio of the foliage at flowering should be betwe en 5 and 10. 3. The tuber yield ranged from 13.4-32.6 t/ha in the N0P0K0-N3P3K3 treatmen ts. The quantity of elements taken up by the tubers + foliage were as follo ws (kg/ha): N 66-180, P2O5 25-69 K2O 55-192, CaO 46-84, MgO 27-42, Fe and N a 2-3, Mn 0.2-0.3, Zn 0.1-0.2, Cu 0.03-0.06. The specific element requireme nts for 1 t tubers + foliage averaged 5.5 kg N, 5.3 kg K2O, 1.9 kg P2O5, 2. 5 kg CaO and 1.4 kg MgO, and were in good agreement with the parameters use d by the Hungarian extension service (with the exception of K2O, where a pa rameter of 9 kg/t is applied). 4. If the foliage remains in the field, the Ca and Mg requirements become n egligible, while the specific K requirement drops to 5-6 kg/t K2O, which is half that given in the literature. The specific requirement of 9 kg/t K2O reflects luxury K uptake, which is frequent on the colloid-poor, intensivel y fertilised soils of North-West Europe. On average sites in Hungary this v alue may lead to over-fertilisation with K.