EFFECT OF BANDED FERTILIZERS ON SOIL SOLUTION COMPOSITION AND SHORT-TERM ROOT-GROWTH .1. AMMONIUM-SULFATE, AMMONIUM-NITRATE, POTASSIUM-NITRATE AND CALCIUM NITRATE

To simulate the effects of banded fertilizer on soil solution composit ion, layers of KNO3, NH4NO3, Ca(NO3)(2).4H(2)O or (NH4)(2)SO4 were pla ced in contact with soil columns and allowed to equilibrate for 5 days at a moisture content equivalent to 10 kPa matric suction. Five soils were used in the columns: 0-10 cm samples from a Kurosol, a Ferrosol, a Vertosol and a Kandosol, and a 50-60 cm sample from the Kandosol. A fter the contact period, soil sections were recovered at successive 5 mm increments from the fertilizer layer, the last section being 45-50 mm from the layer. Soybean seedlings (Glycine max (L.) Merr. cv. Forre st) were grown for 48 h in each section and relative root elongation ( RRE) was determined. Soil solution was then extracted from each sectio n and analysed. Nitrate salts moved 50 mm in all soils (measured as a change in the electrical conductivity of the soil solution), but the m ovement of the sulfate salt was dependent on soil type and was least i n the Ferrosol. As distance from the fertilizer band decreased, concen trations of cations in the soil solution increased, often reaching a p lateau value. In all soils, solution Ca concentrations near the (NH4)( 2)SO4 fertilizer band were lower than those further away, indicating p recipitation of CaSO4.2H(2)O had occurred. This effect was particularl y evident in the Vertosol and Ferrosol. The relationship between elect rical conductivity of the soil solution (EC(ss)) and Ca activity ratio (CAR) was dependent on soil type and fertilizer source. For the sulfa te source, all soils exhibited a common curvilinear relationship in wh ich CAR decreased with increasing EC(ss). However, for the nitrate sal ts, the Ferrosol and Vertosol had a higher CAR for a given EC(ss) than the other soils because of the higher Ca2+ activities in their soil s olutions. Relative root elongation decreased curvilinearly with increa sing EC(ss), and a common curve was obtained for all soils and fertili zer sources. Although CAR decreased with increasing EC(ss), there was no common curve relating RRE to CAR for all soils and fertilizer sourc es. Osmotic effects, and not a salt-induced Ca deficiency, were theref ore considered responsible for the decrease in RRE as distance from th e fertilizer source decreased. A 10% reduction in RRE occurred at an E C(ss) of 4 . 1 mS cm(-1).