Articles
UPTAKE OF NUTRIENTS BY TREES GROWN IN HERBICIDE STRIPS
This concerns distribution in vertical as well as in horizontal direction across the tree rows.
For instance, when the mulched herbicide-treated tree strips take up 40 per cent of the total orchard area, 70 per cent of the fibrous roots may be found in these strips and when rooting depth is 80 cm, some 25 per cent of these roots may be concentrated in the uppermost 10 cm of the soil in the tree strip, consequently 18 per cent of the roots may then occupy only 5 per cent of the total rooted soil volume.
During dry periods in the first months of the growing season, differences in soil moisture content between the grass strip and the weed-free tree strip equivalent to 40 mm in the 0–60 cm layer, or even 20 mm in the 0–20 cm layer, are not uncommon.
In a country-wide soil testing survey, Van der Boon and Das (1978) found higher contents of 0.1 N HCl-soluble K (soil/extractant ratio 1:10) in the 0–20 cm layer of tree strips than in the grass strips.
The differences amounted to a maximum of 750 kg K ha-1 (average 310 kg K ha-1) of tree strip area.
Differences in phosphorus, soluble in ammonium lactate-acetic acid (Egner-Riehm method) amounted to 1100 kg P as a maximum, the average being 250 kg P ha-1. Magnesium contents were sometimes, but not always, higher and pH was usually somewhat lower in the tree strips.
In my own trials, the nitrate-nitrogen content in the 0–60 cm soil layer in the tree strips of unfertilized orchards during April-May was higher by 20–60 kg N ha-1 than that of the grass strips.
When the mown grass was mulched on the tree strips this difference could further increase by 10–20 kg N ha-1 during the summer months, provided precipitation was normal.
In orchards receiving moderate broadcast dressings of nitrogen, tree strips contained 100–150 kg more nitrate-nitrogen than grass strips.
In all cases the average contents in the rooted soil of the grass strips during April-June did not exceed 5–15 kg N ha-1.
Differences in nutrient contents between the untilled herbicide-treated strips and grass alleys depend on factors such as soil properties, fertilizer practice, quantity of grass mowings deposited on the herbicide strip, duration of the strip system and weather conditions.
Horizontal and vertical