Versatile, capable K
Argentina is responding to a challenge - but at a cost. Exceptional growth in crop productivity over the last 25 years has been fuelled, in part, by the natural fertility of the soil. As IPI is able to demonstrate, continuing soil-K mining leads inevitably to weaker plant growth and increasing susceptibility to stress. Potash should not be overlooked if the challenge to produce higher yields is to be met in future.
Argentinian fields have taken on a very different aspect in recent years. Cereals now occupy less than half the cultivated land area, a big drop from the 78% recorded 25 years ago. Making up the difference are oilseeds, notably soybean. Over the last decade, Argentina's exports of cereals and oilseeds have increased from 18.8 million t (Mt) to 33.7 Mt and, as a result, a considerable amount of potassium, contained in the seeds and oilseed cake/meal, has been lost. This K 'export' has doubled over the same decade from around 220,000 t to currently around 400,000 t K2O and the deficit between use of potash and removal by crops is now more than 1.5 million t K2O annually.
Potassium is a versatile nutrient in plants and is involved in many metabolic processes. Without adequate potassium, plants are unable take up and transport efficiently nitrogen (from the roots to the shoot) or carbon (from the shoot to the roots and other storage organs of the plant). In other words, plants cannot be forced to take up more nitrogen if potassium is in short supply. This inhibits growth and vigour, reducing quantity and quality of yields. Research has shown that when crops are subjected to drought stress, the reduction in yield is minimized if there is adequate soil K. This is partly because K is involved in the control of the plant's stomata, the leaf apertures through which carbon dioxide is absorbed and water released in respiration. More efficient control of stomata results in more efficient control of the plant's water budget and, therefore, in times of drought, of water loss.
If the ratio of potassium to nitrogen is out of balance, plants develop soft tissue which is highly vulnerable to chewing and sucking insects or the penetrating hyphae of fungal diseases. Plant breeders may do much to build resistance into varieties but their efforts, and the cost of the seed, is wasted if plant nutrition is unbalanced.
It will be much less costly, in Argentina as elsewhere, to address the issue of restoring balanced soil fertility sooner rather than later and before the point at which the chemical soil properties are so changed that yields are badly affected - and the momentum of the last decades is lost.