The impact of fertiliser magnesium and potassium on the seasonal herbage magnesium concentration of some South Island dairy pastures

摘要

Herbage magnesium (Mg) concentrations were monitored for various Mg fertiliser regimes on dairy pasture at three West Coast dairy sites, for 2-4 years and one site at Methven, for one year. Treatments included three annual Mg rates compared against untreated pasture. Plots were duplicated and sampled prior to each grazing. On all sites, herbage Mg levels cycled through the year irrespective of Mg usage or rate of application and were generally at their lowest in the spring and highest in summer. On all sites mean herbage Mg levels lifted with increasing rate of fertiliser Mg On one site continuous Mg application for four years lifted herbage levels permanently above 0.2 % in the last year At a fifth site in North Canterbury where different rates ofpotassium (K) were used for three years, K fertiliser caused minimum depression in herbage Mg levels, except in the most responsive and driest second season when 120 kgK was used Mean Mg concentration declined at all K rates as the effects of an initialMg application of 20 kg Mg/ha wore off.