| Summary: | Coastal sandy soils, in general, have low fertility because mainly nitrogen
losses due to leaching and volatilization. To reduce N losses and increase growth
and yield of shallot in coastal sandy soils, Urea fertilizers can be coated or mixed
with humic-calcium (humic-Ca). This main study aimed to find out kinds of
humic-Ca concentrations which gave the lowest leaching and volatilization N, and
the highest growth and yield of shallot in coastal sandy soil. This study consisted
of three experiments i.e: (1) laboratory experiment, (2) green house experiment
and (3) field experiment at the coastal sandy land of Bugel, Kulon Progo. The
study was carried out from March 2008 to April 2009. The results showed that
Urea coated with humic-Ca from cow manure and humic-Ca from peat increased
the N total and available N higher than Urea mixed humic-Ca from cow manure
and humic-Ca from peat in the soil. Compare to all treatments, Urea coated with
humic-Ca in all concentration showed nitrate higher than ammonium on
incubation length 2, 4 and 6 weeks. Urea coated with humic-Ca 10% was less
pronounced in reducing N leaching compared to other treatments. The greatest
percentage reduction N volatized on humic-Ca concentration 10 % was 21.21%.
Humic-Ca Urea fertilizer can increase the total soil pore. Improved soil pores
mainly occur in slow drainage pores showing significant differences with Urea.
Increased soil porosity have positive correlation with some soil chemical
properties of coastal sandy soil, such as total nitrogen content, NH4
+, NO3
-,
organic matter, pH, exchangeable Ca and CEC. The humic-Cacow material
provided as a coating of urea has not been able to increase significantly the soil N
availability, growth and yield of shallot in the coastal sandy soil than Urea mixed
the humic-Ca. The availability of N due to the addition of humic-Cacow material
negatively correlated with microbial population ammonification microbial, but
positively correlated with soil microbial populations of nitrifying. Urea coated
humic-Cacow 50% dose recommendations for optimum growth and yield of shallot
in the coastal sandy soil.
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