Soybean makes its demands
Argentine 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 nearly doubled and so too has the 'export' of potassium (K) contained within the seeds and oilseed cake and meal.The deficit between the application of potash as fertilizer, and its 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 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, particularly of oilseeds which are heavy users of K. 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, and hence 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 soil chemical properties are so changed that yields are badly affected - and the momentum of the last decades is lost.
