Use of calcium in bareroot pine nurseries

Abstract

Bareroot nursery managers may apply dolomite, gypsum, or Ca-nitrate to increase Ca in nursery soils. Although a few managers follow S.A. Wilde’s recommendations and maintain soil at levels of 500 to 1,000 μg g-1 Ca, there is no need to keep Ca levels this high.  In contrast, managers at sandy nurseries apply Ca when soil tests drop below 200 μg g-1 Ca. In fact, acceptable pine seedlings have been produced in irrigated soil with <100 μg g-1 available Ca. In plantations, asymptomatic wildlings grow when topsoil contains 17 μg g-1 Ca. In sandy soils, applying too much gypsum can result in a temporary Mg deficiency and too much lime will result in chlorotic needles. Managers apply Ca when foliar levels fall below a published “critical value.” The belief that the critical value for Ca varies by stock type is not valid. In fact, numerous “critical” values are invalid since they were not determined using growth response curves. Critical values determined for small seedlings using CaCl2 in sand are apparently not valid for use in bareroot nurseries.   At bareroot nurseries, the soil extractable Ca level can decline during a year by 30 μg g-1 or more. Harvesting 1.7 million pine seedlings may remove 20 kg ha-1 of Ca but irrigation can replace this amount or more. When water contains 5 mg l-1 Ca, 600 mm of irrigation will add 30 kg ha-1 Ca.  In some areas, 1,000 mm of rainfall will supply 7 kg ha-1 Ca. Even when a Mehlich 1 test shows no exchangeable Ca in the topsoil, pine needles on tall trees may exceed 2,000 μg g-1 Ca due to root growth in subsoil. There are few documented cases of deficient pine needles (<300 μg g-1 Ca) in irrigated nurseries in Australia, New Zealand, Scotland and in the Americas. Even when soil fumigation delays the inoculation of ectomycorrhiza, bareroot pines have adequate levels of Ca. Typically, foliage samples from pine nurseries contain at least 1,000 μg g-1 Ca. Samples from 9-month-old seedlings range from 300 to 11,000 μg g-1 Ca. Although the “critical value” for Pinus echinata foliage is not known, 1-0 seedlings with 300 μg g-1 Ca were not stunted and apparently grew well after ouplanting.