Management of cotton fertilization under drought conditions:
Scientific research in recent years has highlighted drought as one of the most decisive factors limiting cotton productivity. Observations from experimental fields in various regions of Greece confirm that water shortage has a catalytic effect on both the growth and nutritional balance of the crop, requiring specific adjustments in fertilizer doses.
How does drought affect the cotton crop?
Trophobias
Cotton plants grown in dry conditions have a reduced absorption capacity. In particular, insufficient soil moisture dramatically reduces the availability of nitrogen, potassium and phosphorus, as these elements are transported to the roots mainly through diffusion in the soil solution. In experimental measurements of fields under prolonged drought conditions , leaf nitrogen content was reduced by 35-40% in fields.
Development
Osmotic stress caused by drought directly affects the swelling of cells, leading to characteristic symptoms such as:
- Reduced plant height (often 20-35% lower than normal)
- Limited leaf area
- Shorter interstitial space length
At the same time, photosynthetic capacity is dramatically reduced, limiting the production of carbohydrates necessary to support the reproductive organs.
Production
Observations from growing seasons with severe drought show that lack of water during the critical period of flowering can reduce fruit set by 40-60%. Particularly sensitive is the nut formation phase, where drought causes increased drop of combs and young nuts, dramatically reducing the final yield.
Lubrication in dry conditions
Nitrogen Fertilization
Recent studies show that in dry conditions a 20-30% reduction in nitrogen doses is recommended compared to the usual recommendations. For example, if the typical rate is 14-16 units of nitrogen per acre, in dry conditions about 10-12 units are recommended.
However, the form of the nitrogen fertiliser plays a decisive role. It has been found that nitrate forms (e.g. ammonium nitrate 33,5-0-0) perform better in drought conditions, as they are more easily absorbed by the plant even with limited soil moisture.
Calico Lubrication
Potassium proves particularly valuable under water stress conditions. In an experimental field in Larissa, it was observed that an increase in potassium fertilization by 15-20% significantly improved the drought resistance of plants, leading to an 18% higher yield compared to plots receiving standard fertilization.
It is recommended to apply potassium fertilizers in 2-3 doses in the following proportions:
- 40% implanted
- 30% with the first irrigation (if possible)
- 30% before flowering
This tactic avoids increasing salinity which would exacerbate water stress.
Phosphate fertilization
Phosphorus is critical for the development of the root system. From observations in fields in Boeotia, it was found that plants that received adequate phosphate fertilization preplanting developed a root system with 25-30% greater volume, thus improving their ability to draw water from deeper soil layers.
It is recommended to apply 5-6 units of phosphorus per hectare, with the total amount applied sparingly and at a depth of at least 10 cm for better utilization.
Interfacial Applications
In times of prolonged drought, trans-wave spraying proves to be a lifesaver. Trials have shown that a combination of potassium (2-3%) and trace elements during the flowering phase can increase the drought resistance of plants and reduce comb fall by 15-20%.
Integrated Crop Management
Improving the soil
The addition of organic matter can increase the water capacity of the soil by 20-30%. In fields where this practice has been applied for three consecutive years, significant improvements in soil structure and increased drought resistance have been observed.
Drip irrigation and hydro-fertilisation
Fertilizer application through drip irrigation (fertigation) is probably the most efficient method in conditions of limited water availability. Tests have shown that hydrofertilisation can improve fertiliser use efficiency by 30-40%, while reducing overall water requirements in semi-arid conditions.
