Soil mineral nitrogen variations and nitrogen uptake of maize in an amended compacted soil
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Date
2014-07-13
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Abstract
Soil compaction is a major problem affecting soil quality in contemporary crop
production due to mechanized operations on crop fields. The ameliorative/
compensatory effect of soil amendment on soil compaction has been reported in
literature. However, the impact of soil amendment on mineral N dynamics and uptake
by crops in compacted soils is yet to receive the needed research attention especially
in Ghana. To bridge this gap in knowledge, field and pot experiments were
respectively conducted at the Agricultural Research Station, Anwomaso, KNUST and
the Mechanization Section of Agricultural Engineering Department, KNUST to study
NH4
+
and NO3
-dynamics and crop uptake in compacted soils amended with poultry
manure. Soils were compacted to three levels of soil bulk densities (1.3, 1.5, and 1.7
Mg m
-3
) in the field experiment whilst that of the pot experiment was compacted to
four bulk density levels (1.3, 1.5, 1.7 and 1.9 Mg m
-3
). The compacted soils in both
experiments were amended with two levels of poultry manure at 4 and 6 t ha
-1
with a
control (0 t ha
-1
). The study was a factorial experimental laid out in randomized
complete block design for field and completely randomized design in the pot
experiment with three replications. Parameters measured were plant height, stover
weight, crop N uptake, root length and biomass, microbial biomass carbon and
nitrogen, ammonium and nitrate - nitrogen. The results revealed that soil compaction,
poultry manure amendments and their interactions significantly influenced (P < 0.05)
mineral N levels, N uptake and agronomic characteristics of maize. Mineral nitrogen
(NO3
--N and NH4
+
-N) generally increased from 21 to 42 days after amendment
(DAA) and declined at 63 DAA in both experiments. Levels of NO3
--N (7.10 – 61.90
mg N kg
-1
soil) were higher than that of NH4
+
-N (5.69 – 36.78 mg N kg
-1
soil)
suggesting more losses of N from the system since N stored in the form of NO3
-is
iii
subject to more leaching losses than NH4
+
. Soil compaction generally resulted in
decreased NO3
--N and NH4
+
-N levels, however, applications of poultry manure was
associated with a significant (P < 0.05) increase in mineral N levels in both
experiments. Generally, amendment and compaction interacted to significantly affect
NO3
-levels. The results obtained revealed that the main effect of soil compaction did
not influence soil microbial biomass. However, the interactive effect of bulk density
and amendment significantly (P < 0.05) influenced microbial biomass carbon and
nitrogen contents of the soil such that the highest microbial carbon was recorded under
4 t ha
-1
poultry manure in soil bulk density of 1.3 Mg m
-3
and the highest biomass N
recorded in soils of bulk density of 1.3 Mg m
-3
treated with 6 t ha
-1
poultry manure.
Application of 6 t ha
-1
poultry manure significantly (P < 0.05) increased N uptake and
grain yield of maize crop in both experiments. Maximum N uptake were observed
when poultry manure was applied at the rate of 6 t ha
-1
on soil of bulk density 1.3 Mg
m
-3
. The highest grain yields of 3004 kg ha
-1
and 2453 kg ha
-1
were respectively
obtained in field and pot experiments. Plant height, stover yields, root length and
biomass generally increased in amended plots over the control plots. However,
increasing bulk density beyond 1.5 Mg m
-3
significantly decreased these parameters.
Description
A thesis submitted to The Department of Crop and Soil Sciences, Faculty of
Agriculture, College of Agriculture and Natural Resources, Kwame Nkrumah
University of Science and Technology, Kumasi, Ghana, in partial fulfillment of
the requirements for the award of the Degree of Master of Philosophy in Soil Science, 2014