Nutrient studies in potatoes (Solanum tuberosum)

Abstract

One of the biggest problems facing potato (Solanum tuberosum) production in Kwazulu-Natal is acidic soils with high a aluminium content. Traditionally, such soils were ameliorated using lime, thus increasing soil pH, Ca and Mg availability, and reducing Al availability. This study aims to determine the extent to which lime could be replaced by Calmag+B (a Ca source with little ameliorative capacity). The Calmag+B fertiliser increases the soil's Ca content appreciably, but does not alter soil pH and Al availability to the same extent as lime. Pot trials were carried out to determine the effects of liming a highly acid soil, resulting in four levels of amelioration. At each level of amelioration, three levels of Calmag+B were applied to determine whether an optimised yield response would be attained through these applications. Plant emergence and subsequent development was shown to be poor, and in extreme cases absent, under highly acidic soil conditions. Soil amelioration using lime greatly improved plant emergence, development and tuber yield, whereas Calmag+B applications were unable to improve plant emergence, development or tuber yield. The effect of both applications of substantial quantities of Calmag+B to a highly acid soil, and of the dipping of mother tubers in a nutrient solution prior to planting was investigated. The Calmag+B soil applications were unable to improve plant emergence and development. The dipping of the mother tubers in nutrient solution, however, resulted in greatly increased seedling emergence and plant development. This was due to increased nutrient uptake from the mother tuber, and not through increased root development and subsequent nutrient uptake. There were unsubstantiated claims by the manufacturers of Calmag+B that the Mg, NO(3) and B components of the fertiliser would give rise to increased uptake of the Ca component, thus enhancing the efficacy of the fertiliser. Pot trials using a sand medium were employed to test this claim. The trial consisted of interactions of different levels of Ca(2+), Mg(2+), NO(3-), and BO3(2-) applied to the sand medium in the form of a nutrient solution. None of the treatments (barring Ca itself) led to increased Ca uptake by the potato tubers. This would indicate that the claim that the Mg, NO(3) and B components of Calmag+B fertiliser would enhance the uptake of the Ca component are unfounded. It has been suggested that one of the main factors limiting potato production in Kwazulu-Natal has been inadequate mineral nutrition. Certain fertiliser distributors claim that fertiliser application over and above the levels recommended by the Kwazulu-Natal Department of Agriculture Fertiliser Advisory (KDAFA) is the solution to the problem of below potential yield and tuber quality in the province. A field trial was carried out in New Hanover (Kwazulu-Natal), using different levels of Calmag+B and Agrifos, as well as one level of application of KNO(3). All treatments were applied after KDAFA fertiliser recommendations had been fulfilled. At the 95% level of significance, the treatments did not give rise to increased yield and tuber quality. At the 80% level of significance, however, the results indicated that applications of 100kg ha -1 of Calmag+B and KNO(3) would give rise to increased tuber yield.