The effects of soil compaction, form of nitrogen fertiliser, and fertiliser placement on the availability of manganese to barley

Abstract

AbstractA study was made of the effects of seedbed compaction and use of fertiliser (application rate, placement, and the choice of ammonium or nitrate forms of nitrogen) on the availability of manganese to barley in light soils in East Scotland. Generally, the uptake of manganese by the plants was increased by increasing the amount of fertiliser applied and by compaction of the seedbed, although no significant increase in extractable soil manganese was detected. The increase in uptake from wheel‐tracks (where the compression had resulted in an element of fertiliser placement), compared with nonwheeled areas, was much greater than the effect due to overall plot compaction by tractor wheels in the absence of a fertiliser placement effect. Combine‐drilling of fertiliser with the seed resulted in large increases in plant uptake of manganese in non‐wheeled areas, compared with uptake where the fertiliser had been broadcast, but had no significant effect in the wheel‐tracks where growth and uptake were generally better. In some, but not all, experiments, significant reductions in pH occurred in the soil beneath the wheel‐tracks which were very closely correlated with increases in extractable manganese. Use of ammonium sulphate as nitrogen source also reduced the pH, compared with calcium nitrate, and this, too, increased extractable manganese and greatly improved plant growth. The probable cause of enhanced manganese availability was soil acidification brought about by nitrification of ammonium fertiliser and/or by H+ ion secretion by roots to balance the uptake of ammonium and other cations. The uptake of manganese by the plant was further improved either through concentration of fertiliser in the root zone by placement, or by soil compaction which resulted in shallow sowing of seed and a closer active relationship between roots and broadcast fertiliser. Other possible factors involved were (a) a greater exudation by roots of compounds able to dissolve insoluble manganese, in compacted soil; (b) contact reduction processes; (c) stimulation of root growth, leading to more efficient uptake by the plant, where higher rates of fertiliser were used or where the fertiliser was concentrated in localised zones in the soil.