Soil mineral nitrogen variations and nitrogen uptake of maize in an amended compacted soil

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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.
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