Effect of banded fertilizers on soil solution composition and short-term root-growth .2. Mono-ammonium and di-ammonium phosphates

Abstract

A layer of mono-or di-ammonium phosphate (MAP and DAP, respectively) was placed in contact for 5 days with duplicate columns of soil at a water content equivalent to 10 kPa matric suction. This was designed to simulate the effects of banded fertilizer on soil solution composition. Five soils were used: 0-10 cm samples from a Kurosol, a Ferrosol, a Vertosol and a Kandosol, and a 5 M 0 c m sample from the Kandosol. After the contact period, soil sections were recovered at successive 5 mm intervals from the fertilizer layer, the last section being 45-50 mm from the layer. Soybean (Glycine max (L.) Merr.) seedlings were grown for 48 h in each section and relative root elongation was determined. Soil solution was then extracted from each section and analysed.The amount of inorganic P in the soil solution (Pi) was summed over all soil sections for each soil and each P source and was found to be correlated with distance of P movement from the simulated band ( r = 0.792, P < 0.01). Of several soil chemical parameters of the control (unfertilized) soils regressed against Pi, the following showed significant ( P = 0.05) negative correlations: Ca and Mg concentrations in the soil solution for Pi from both MAP and DAP, exchangeable Ca and Mg for DAP, and citrate-dithionite extractable Fe and A1 for MAP. These results suggest that adsorption (and possibly precipitation) reactions with Fe and A1 hydrous oxides contributed to the removal of Pi from solution in the presence of MAP. However, with DAP as the fertilizer source, precipitation reactions involving Ca and Mg were the predominant factors. Dissolved organic C in the soil solution increased adjacent to both DAP and MAP, with larger amounts in proximity to DAP being a consequence of the higher soil solution pH (-7). Soil solution Si increased in all soils adjacent to both DAP and MAP, with concentrations being higher in the MAP treatments. Dissolution of aluminosilicates in the acidic conditions near MAP (pHw5) was the probable cause.Relative root elongation (RRE) of soybean was restricted in soil sections close to the fertilizer. When RRE was plotted against each of soil solution EC, NH3 activity, and calcium activity ratio (CAR), a single curvilinear function described the relationship between RRE and CAR for all soils and both P sources. It is concluded that a salt-induced Ca deficiency was the cause of restricted root growth in proximity to DAP and MAP, rather than an osmotic effect or NH3 toxicity.

Effect of pH on Na induced Ca deficiency

“…Critical CARs of 0.097 (Menzies et al, 1994) and 0.06 (Hailes, 1998) have been reported for mungbean, 0.047 (Bruce et al, 1988) and 0.058 (Moody et al, 1995) for soybean (Glycine max), 0.10 for peanut (Arachis hypogaea) (Wolt and Adams, 1979), 0.15 for Sudan grass (Sorghum sudanensis) and cotton (Gossypium hirsutum) (Bennett and Adams, 1970), and 0.10 to 0.15 for cotton (Gossypium hirsutum) (Adams, 1966;Howard and Adams, 1965).…”

Potato Yield and Tuber Set as Affected by Phosphorus Fertilization

“…When MAP dissolves in the soil it initially results in an acid reaction, while DAP initially results in an alkaline reaction (Moody et al 1995). Because of this pH effect and the fact that P availability is maximized at near neutral to slightly acid pH levels (Tisdale and Nelson 1975), MAP is potentially more effective on alkaline soils and DAP may be more effective on acid soils.…”

Densely rooted rhizosphere hotspots induced around subsurface NH4 +-fertilizer depots: a home for soil PGPMs?

“…The NH 4 + tolerance threshold for our tested PGPMs (50-250 mM NH 4 -N) is also above the range of 2-20 mM that can be common in soil solution of most agricultural soils [42]. The range is also above the NH 4 -N concentrations that can be measured in soil solution a few centimeters from a subsurface NH 4 + -fertilizer band (extracted by centrifuging soil samples collected a few centimeters from a subsurface NH 4 + -fertilizer band (< 0.001-37 mM NH 4 -N and 0.4-91 mM NH 4 -N from a distance 4-2 cm to a fertilizer band of (NH 4 ) 2 S0 4 ) and di-ammonium phosphate, respectively, after 5 days of contact of bands with soil, for tests on five different soil types) [43,44].…”