A silócirok (Sorghum bicolor L. Moench) szárazanyag-felhalmozása és tápelem-felvétele | Dry matter accumulation and nutrient uptake of forage sorghum (Sorghum bicolor (L.) Moench)

The aim of the work was to study the effect of N, P and K supply levels on the dry matter accumulation and nutrient uptake of forage sorghum in order to develop fertilisation recommendations for sorghum The long-term fertilisation experiment was established in 1989 on a chernozem meadow soil calcareous in the deeper layers and involved all possible combinations of 4 levels each of N, P and K, giving a total of 64 treatments. Nine treatments were selected for the present study. The main results of experiments performed between 2002 and 2004 can be summarised as follows: 1. By the 7–8-leaf stage, 30 days after emergence (GS3), the forage sorghum had accumulated 29% of the total green mass and 8% of the total dry matter. During the subsequent intensive growth period, till the beginning of heading (GS5–6), 74% of the total green mass and only 38% of the total dry matter was accumulated. The green mass reached its maximum at physiological maturity (GS9). Approximately 60% of the dry matter accumulation occurred in the generative stage. 2. On chernozem meadow soil with 2.8–3.2% humus content the application of 80 kg·ha ⁻¹ N fertiliser alone did not result in a significant increase in the N content of the sorghum compared to the unfertilised treatment, but if P was added there was a significant increase in the N concentration. In soil with a P-supplying capacity of 195–222 mg·kg ⁻¹ AL-P ₂O ₅ no further significant N increase was observed at N application rates of over 80 kg·ha ⁻¹. Excessive levels of soil P and K, above 340 mg·kg ⁻¹ AL-P ₂O ₅ and 450 mg·kg ⁻¹ AL-K ₂O, had no significant influence on the N content of the plants. 3. Compared to the treatment without P fertiliser addition, where the AL-P ₂O ₅ content of the soil was 120–139 mg·kg ⁻¹, only an excessive level of P (340–360 mg·kg ⁻¹ AL-P ₂O ₅) resulted in a significant increase in plant P content at the beginning of heading and at flowering. 4. On the soil with good K supplies a significant increase in the K concentration of sorghum plants was only observed at the 7–8-leaf development stage in the case of excessive K status (450 mg·kg ⁻¹ AL K ₂O). 5. In the fertilisation treatments with the highest yield (56–58 t·ha ⁻¹ green mass) 65–70% of the total N was taken up by the flowering stage (GS6–7) and almost 1/3 during seed formation. The dynamics of P uptake was more moderate than that of N. P accumulation was most intensive during flowering and seed formation, when 57% of the total P was incorporated. The K accumulation of sorghum was more intensive in the first half of the growing season than the N and P accumulation. Over 90% of the total K accumulation had taken place by the flowering stage. In the vegetative phase, up till the boot stage, 52% of the total Ca and Mg and 54–58% of the total Fe, Mn, Zn and Cu were accumulated. 6. The specific nutrient content in treatments with the highest fresh (56–58 t·ha ⁻¹) and dry matter yield (19–21 t·ha ⁻¹), calculated in terms of 10 t fresh mass, amounted to 57 kg N, 12 kg P (28 kg P ₂O ₅) and 55 kg K (66 kg K ₂O). Averaged over the fertilisation treatments the specific nutrient content in 10 t fresh mass amounted to 2.6 kg Na, 9.5 kg Ca (13 kg CaO), 9.3 kg Mg (15 kg MgO), 388 g Fe, 185 g Mn, 67 g Zn and 21 g Cu.