EFFET DE LA FERTILISATION POTASSIQUE SUR LE RENDEMENT DE LA POMME DE TERRE EN RELATION AVEC L’ANALYSE DU SOL

Abstract

The effects of potassium fertilization on potatoes (Solanum tuberosum L.) grown on 40 experimental sites were related to tuber yields and soil test values. The data used in this work were gathered by seven research groups over a 25-yr period. Concentrations of exchangeable potassium (1 N NH4OAc, pH 7.0) in soils ranged from 28 to 462 kg K/ha. About 68% of the soils were classed as having a poor supply of available potassium, according to the criteria used until now in Quebec, because they contained less than 200 kg K/ha. A Mitscherlich exponential equation was fitted to the relationship between the percent of maximum yield and the concentration of available K in soils (R2 = 35.9%). The Cate-Nelson procedure was also used for ranking soils in three potassium fertility classes as indicated by their relative yields without K fertilization. The following classification of soil K levels was obtained: poor, soils containing less than 140 kg K/ha; intermediate, those containing between 141 and 300 kg K/ha; and sufficient, those containing more than 300 kg K/ha. The percent of maximum yield ranges obtained without K fertilization by these different soil fertility classes were: poor, from 34 to 98% with an average of 74%; intermediate, from 88 to 100% with an average of 95: and sufficient, from 93 to 100% with an average of 98%. The fertilization rates required to obtain or maintain maximum yields by these respective classes were 175, 130 and 80 kg K/ha. Potassium fertilization increased yields significantly on the soils that had a poor K supply only. Nonetheless, the average tuber yield indicated that a 5% increase in yield might be obtained with K fertilization on the intermediate soils and this increase would easily be profitable. Potassium fertilization of the soils classed sufficient would, however, only maintain soil fertility by supplying part of the K requirement of this crop.