Introduction

Crop growth and productivity depend upon environmental conditions such as radiation, temperature, water supply and nutrient availability. In many areas of the world the occurrence of drought has become more frequent and research on overcoming drought stress is required.

In Poland, which is on the border of the maritime and continental climate, shortterm drought periods are frequent and depress yields especially in the sandy soils, which cover 60 per cent of Poland's agricultural land. One of the many functions of potassium in plants is the regulation of the osmotic potential and turgor in plant cells, i.e. control of water consumption. The following experiments were conducted in order to investigate the role and contribution of potassium in triticale and sugar beet production under two different periods of induced drought.

Methods and materials

To evaluate the effect of water and K availability on crop yield, two field experiments were established at the Brody Research Station (Agricultural University of Poznań, Poland). The experimental soil was loamy sand with a neutral reaction and a potassium content of 14 mg K₂O/100 g (Double Lactate method). Two crops were tested, triticale (1993 - 1995, 3 seasons) and sugar beet (1998 - 2000, 3 seasons). The two-factorial trial consists of two potassium application rates (0, 100_triticale/150_{sugar beet}) and four different water management regimes (Table 1).

A static plastic shelter, covering the experimental area of 72 m² was used to obtain soil moisture stress at particular stages of growth of the two crops. Nitrogen and phosphorus were applied at 100 and 30 kg/ha for triticale and 120 and 50 kg/ha for sugar beet, respectively. P and K-fertilizers were provided as a basal dressing before seeding and planting, and nitrogen supplied twice in an equally split application in two split applications.

Results and discussion Triticale

The highest yields were achieved, when fields were irrigated and these were closely followed by plants grown under rainfed conditions (Fig. 1). Inducing drought reduced yield considerably; the effect being greater when water shortage occurred during stem elongation (June), as compared with during flowering (July).

Potassium fertilization was beneficial in all treatments, producing 1.33 mt/ha additional grain production and an agronomic efficiency of K of 13.3 kg (AE_K, kg grain/kg K₂O). The yield increase under full irrigation was only 6 per cent, whereas under rainfed conditions as much as a 22 per cent additional yield was recorded, when 100 kg/ha K₂O were applied (Fig. 1).

Under drought conditions, K application had a tremendous effect on grain yield. When the drought period occurred at stem elongation, the application of K increased yield by 63 per cent, from 3.1 mt/ha to 5.06 mt/ha (drought June). This effect on yield was slightly lower, when water shortage occurred at flowering (drought July), nevertheless with an additional yield of 1,900 kg/ha it is still impressive. In both drought treatments, AE_K was very high at approximately 19 kg grain per 1 kg of potassium applied. The 3-years field trial with induced drought periods clearly demonstrates that an adequate supply of K could markedly reduce the impact of drought on grain yield of triticale, and can be considered as an 'insurance policy' for erratic rain conditions.

Sugar beet

Both experimental factors, water treatments as well as K application, influenced the final average yields of sugar beet roots of the three year trial (Fig. 2). Potassium fertilization resulted in an average yield increase of 8.25 mt/ha, taking into account all four water treatments. The average AE_K was 55 kg of sugar beet per kg of potassium, and was much higher with irrigation, AE_K being increased to 79 kg of sugar beet per kg potassium applied. The highest yield (62.0 mt/ha) was obtained from both K fertilized and irrigated treatment. This treatment also showed the largest effect of K application, which resulted in an additional yield of 24 per cent (Fig. 2). Induced drought had a significant effect on root yield and, compared to the rainfed treatment, the yield of beets at harvest was lower by up to 9 mt/ha. There was not much difference in the yield response, whether the drought period occurred during July or August. Potassium fertilization increased the beet yield by 17 per cent (drought in August) and 20 per cent (drought in July). Both experimental factors had only a small effect on sugar content (approx.16.7%), α-amino N, K and Na content, and therefore the refined sugar yield followed the same pattern as the root yield.

Conclusions

The need for an adequate water supply and a balanced K fertilization was demonstrated in trials with triticale and sugar beet in experiments carried out over a period of three years. In both crops, potash application had a pronounced effect in increasing yield, by helping to alleviate the depressive effect of drought. Potash application can be considered as an 'insurance policy' and should be made annually. Potash application also raised yields under natural precipitation, without any obvious periods of water restriction. It is concluded that potash fertilization, at 100 and 150 kg K₂O/ha in triticale and sugar beet, respectively, is cost effective when regular precipitation occurs, and has a dramatic effect on yield under drought conditions.

References

• Grezbisz W. et al 1993, 1994, 1995: Trial reports on drought stress of triticale.
• Grezbisz W. et al 1998, 1999, 2000: Trial reports on drought stress of sugar beet.
• Wyrwa P., Grezbisz W. & Diatta J.B. 1998: The effect of simulated drought and potassium fertilization on spring triticale growth and yield. Internal report.
• Grzebisz W., Musolf R., Barłóg P. & Potarzycki J. 2002: Potassium fertilization, water shortage during vegetation and crop yielding variability the case of sugar beet. Biuletyn Instytutu Hodowli I Aklimatyzacji Roślin Nr. 222.

Edited by E. A. Kirkby