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POTASSIUM AND STRESS TOLERANCE
By T. Nagendra Rao
Agriculturally important states like Andhra Pradesh, Karnataka and Kerala in the South are often susceptible to unpredictable rains. Sowing can be delayed in large parts of intensive cropping areas during Kharif season because of scanty and confusing rainfall condition. In areas where sowing has already been done, tough drought-like situations can create panic among many farmers.
Total failure of monsoons in the region is a rare phenomena, however inadequate, untimely rains are quite common. A prolonged dry spell for a certain period of time followed by heavy rains with excess water creates a very unfavorable condition for crops. High humidity due to high moisture may trigger outbreak of pests and diseases. Any of these stresses can seriously limit crop yields.
It is a known fact that adverse conditions such as water stress due to low rainfall (drought), or too much of water (floods) are prime culprits of unfavorable soil condition, thereby seriously impairing crop growth and yields. No one can avert natural calamities but, there are several ways and means to minimize their severity on crops.
Potash has definite role to play !
Many a times potassium is considered as a nutrient to improve crop yields. It is true, but, it's other important role of reducing stress impact on crops is often not realized. Potassium may not prevent drought and flood effects altogether, but it can reduce the effects of adverse moisture conditions on crop growth. Unfortunately, many farmers apply too little potash to crops as they expect quick visual responses in the field as observed with nitrogen.
How Potassium helps minimize water stress?
By way of increased root exploration....
Soil supplied with adequate K along with other essential plant nutrients, good root growth and expansion observed. Greater root branching and penetration means, better access to soil moisture from lower layers. Phosphorus also has similar role to play.
Low soil moisture alters physiological processes in roots. Root elongation, turgidity, and rate of root regeneration are increased with sufficient K.
The main issue is that, inadequate rainfalls or excess water conditions compel farmers to go for under/inadequate fertilization due to uncertainty.
By way of decreased rate of transpiration....
Potassium has a specific role in regulating opening and closing of stomata on the leaf surface. Plants supplied with sufficient K make stomata close quickly and prevent the plant from wilting quickly by unnecessary water loss through transpiration.
By way of quick crop growth....
K as a major plant nutrient speeds crop development thereby reaching maturity very quickly. Severity of the effect of low moisture can be reduced under delayed planting by advancing date of pollination when most crops are highly sensitive to moisture stress.
Research says
In China.....
Experiments conducted at the Ziyang, Sichuan Soil Conservation Research Institute illustrate the specific role of potassium in stress tolerance. Lysimetric studies conducted on corn (maize) indicated that plants could withstand and grow well even at low moisture conditions in presence of K (Fig. 1).
Fig. 1. Performance of corn under water stress with and without K fertilization
In India...
A field experiment on ginger crop at College of Agriculture, Kerala Agricultural University, Vellayani indicated how potassium helps the crop tolerate low soil moisture conditions (Fig. 2).
 Fig. 2. Influence of K nutrition on ginger crop under moisture stress situation (Source : M. Meerabai & T. Nagendra Rao, 1998)
Yield opportunities...
Thousands of field experiments conducted on Kharif rice confirms the fact that crops' response to K fertilization are quite significant under rainfed (dry) conditions compared to irrigated (normal) (Fig. 3). Experiments show that yield increase due to application of 40 kg/ha K2O to un-irrigated rice along with 120-60 kg/ha N-P2O5 is much higher compared to application of 60 kg/ha K2O to irrigated rice at the same N and P levels.
Source: Randhawa and Tandon, Fertilizer News (1992)
How Potassium helps minimize stress due to waterlogging ?
Some times, heavy rains after prolonged dry spells creates water logging and making crops suffer either due to lodging or due to poor aeration.
- K fertilization helps building cellulose thereby giving sturdiness to plant stems. This helps prevent lodging.
- Poor drainage under water logged conditions can reduce soil aeration. This situation make roots starved for oxygen. For optimum growth plant roots require a proper balance (ratio) between solid (mineral & organic ), liquid (water) and gaseous (air) phases in the soil. For most plants, this ratio by volume is about 50:20:30, respectively. If oxygen is lacking, root respiration is affected resulting in reduced K uptake. Where there is a risk of lack of oxygen, K fertilization helps improve plant health.
How potassium helps reducing pest/disease incidence?
Plants become weak as a result of environmental stress and this situation makes plant vulnerable to pest and disease attack. Potassium prominently affects plant health by its involvement in the plant's metabolic growth processes. Potassium deficient plants are susceptible to pest invasion because changes take place in morphology and physiology.
- Potassium fertilization improves plant's structure. This make plants resistant against pest invasion.
- Potassium enriched plants develop barriers to pathogens by way of complete stomatal closure, reduced membrane leakage increased lignification of vascular bundles at cellular level.
Table 1. Effect of K on pest and disease incidence
| Type of Pest | Number of Reports | % of Indications |
Positive | No Effect | Negative |
| Fungal | 740 | 71 | 11 | 18 |
| Bacterial | 68 | 75 | 12 | 13 |
| Virus | 116 | 41 | 14 | 45 |
| Insects/Mites | 231 | 59 | 16 | 25 |
Source: Better Crops International, 1988
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