Leaching of Soil Calcium, Magnesium, and Potassium in Irrigated Orchard Lysimeters

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Abstract
Leaching under intense irrigation and nitrogen fertilization has reduced soil basic cation concentrations and soil pH in irrigated apple orchards. The objective of this study was to measure the effects of N fertilizer and grass cover vs. clean cultivation on Ca, Mg, and K leaching, and to determine the changes in concentrations of these cations in soil and leaf and fruit tissue of ‘McIntosh’ apple trees (Malus domestica Borkh.). Twelve lysimeters, each containing an Osoyoos sandy loam soil and a single ‘McIntosh’ apple tree, have been monitored for Ca, Mg, and K concentration of soil, drainage water, and tree leaves and fruit from 1976 to 1980. Lysimeter treatments included factorial combinations of Kentucky bluegrass (Poa pratensis) and clean cultivation and two N fertilization rates [162 (N1) and 324 kg N ha−1 year−1 (N2) as NH4NO3]. Clean cultivation had the greatest effect on cation leaching with significantly higher Ca and Mg concentrations and higher Ca, Mg, and K losses frequently measured in drainage from these plots. By 1981, exchangeable Ca, Mg, and soil pH at the 0‐ to 0.10‐m soil depth in the cultivated plots had declined by 4.3 mmol kg−1, 2.2 mmol kg−1, and 0.3 units, respectively, relative to the grass plots. Drainage from N2 relative to N1 lysimeters had a significantly higher Mg concentration for 4 years but significantly higher Ca and Mg loss rates in only 1 year because of lack of differences in drainage volumes between N2 and N1 plots. Neither the cultivation or fertilizer treatments had altered Ca, Mg, or K concentration of McIntosh fruit or foliage in 4 years. For all lysimeters, Ca and Mg leached more rapidly than K. Annual losses over all treatments, 1976 through 1980, averaged 387 kg Ca ha−1, 118 kg Mg ha−1, and 44 kg K ha−1. Such leaching would eventually lead to enrichment of local soils with K relative to Mg and Ca. This is undesirable since McIntosh trees are susceptible to Mg deficiency and K:Ca antagonism. Therefore, periodic additions of Ca and Mg as through dolomitic liming should be considered for these orchards. Also, K fertilization accelerates existing trends to relative enrichment of these soils with K.