PH OF STARTER MIXED FERTILIZERS

References: 12th International Multidisciplinary Scientific GeoConference, www.sgem.org, SGEM2012 Conference Proceedings/ ISSN 1314-2704, June 17-23, 2012, Vol. 4, 163 - 168 pp

ABSTRACT

Starter fertilizers are banded near the seed at planting time. Mineral fertilizers
commonly used as starter are monoammonium phosphate (MAP) and diammonium
phosphate (DAP). Recently, organo-mineral fertilizers (OMF) made from mixtures of
DAP, MAP and separated solid fraction of pig slurry with or without composting (SPS)
have been developed in Quebec (Canada). These OMF are used as starter to increase
early plant growth and nutrient uptake. The main objective of this laboratory experiment
was to develop starter mixed fertilizers with target pH between 5.8 and 7.0. In a first set
of experiments, different amounts of MAP were mixed with DAP in order to obtain 0 to
60% MAP in the mineral fertilizer mixture matrix. In a second set of experiments,
different amounts of nine SPS were mixed with two mineral fertilizers (1:1 MAP:DAP,
w/w) in order to obtain 0, 20, 40, 60, 80 and 100% SPS in the final fertilizer mixture
(i.e. OMF). Increasing MAP resulted in decreasing pH of the mineral fertilizers mixture
(MF) from 8.0 (100% MAP) to less than 5.5. The target pH values of 5.8 and 7.0 were
obtained respectively with 50% and 12.6% MAP in the MF. The pH values of the OMF
(SPS + MF) varied from 5.8 (MF without SPS) to 6.0-6.9 (80% SPS + 20% MF),
depending of the type of SPS. The results indicated that the pH of OMF samples
depended on the nature and amount of its components and the buffering capacity of the
OMF. The addition of organic fertilizer such as SPS tends to increase OMF’s buffering
capacity. SPS could be used in increasing proportions (up to 80%) in the OMF as
alternative to ammonium phosphate as starter fertilizer.

Keywords: organic fertilizer, solid pig slurry, pH, buffering capacity.