Fertilisation of sunflower (Helianthus annuus L.) on a calcareous loamy chernozem soil

The effect of different levels of N, P and K fertilisation on the readily a vailable nutrient content of the soil and on the yield, oil %, fatty acid c omposition, yield components and disease resistance of the sunflower hybrid Koflor-2 was studied in 1982 in the 9th year of a long-term fertilisation experiment set up on a total of 128 plots with 4(3) = 64 treatments on calc areous loamy chernozem soil. The annual N rates were 0, 100, 200 and 300 kg /ha, while the P2O5 and K2O rates amounted to 0, 1000, 2000 and 3000 kg/ha over the 9 years. The ploughed layer of the experimental site contained aro und 5% CaCO3, 3% humus and 20% clay, and had a pH(KCI) of 7.3. The soil ana lysis showed the original soil to be satisfactorily supplied with Mg, Mn an d Cu, moderately supplied with N and K, and poorly supplied with P and Zn. The groundwater was at a depth of 13-15 m and the growing site was liable t o drought. Rainfall during the vegetation period amounted to 295 mm, prior to which the soil contained water reserves of approx, 200 mm, The main resu lts can be summarised as follows: 1. The air dry mass of the 6-8-leaf sunflower shoots rose 2.5 times as the result of combined PK fertilisation, while N fertilisation caused mild depr ession. By harvest time the PK effects had disappeared and a moderate (0.3 t/ha) N effect was observed in the achene yield, which could be attributed to an increase in the diameter of the inflorescence, As the NxP supplies im proved, however, the oil content of the seed declined from 50 to 45 %, so t here was no change in the oil yield as the result of the treatments. 2. Sunflower yielded 3.1 t seed, 3.1 t stalk and 1.7 t head (a total of 7.9 t air-dry mass) per hectare. The oil yield was 1.5 t/ha. On similar soils rates of 100 kg/ha N, 120-150 mg/kg AL-P2O5 and 150-200 mg/kg AL-K2O, estim ated with the ammonium lactate method, will ensure a good yield. 3. Excessive nutrient supplies, or over-fertilisation, led not to a greater yield, but to greater susceptibility to diseases and to a decrease in qual ity. The occurrence of Macrophomina phaseolina in the mature crop was four times as high as in the control, especially in plots given combined NxP sup plies, Infection with Alternaria zinniae rose significantly by 8% due to ex cessive K, while infection with Embellisia helianthi was doubled by excessi ve N. The frequency of Sclerotinia sclerotiorum was insignificant in this d ry year, though it also tended to increase with fertilisation (from 0.3 to 3 %). The number of seeds shed from the head was also several times greater in the fertilised plots. 4. The extreme values of 1000-seed mass and oil content ranged from 20-80 g and 40-57%, respectively, for individually examined plants. The seed yield and 1000-achene mass rose with an increase in the inflorescence diameter, while the oil % of the seed declined. There was a great reduction in the 10 00-seed mass and an increase in the oil % towards the middle of the inflore scence. 5. From the agronomic point of view an head diameter of 18-20 cm, a plant d ensity of 45-55 thousand plants ha, achieved with a spacing of 70x25 or 70x 30 cm, and most importantly a uniform stand are desirable. A thin stand res ulting in extremely large flowers or a dense stand leading to very small fl owers will reduce the oil yield. 6. On relatively heavy soils with a satisfactory supply of nutrients sunflo wer is not a crop with a high fertiliser requirement. A seed yield of 3 t/h a can be achieved with approx. half as much N and P fertiliser as a 6 t/ha yield of cereals. The interests of the grower and the oil industry will not clash if the negative correlation between yield and oil % is only moderate ly manifested.