Laboratory studies and field trials were carried out to investigate the effect of
addition of some organic residues to acid soils on soil pH, exchangeable and
soluble AI, nutrient status, microbiological and biochemical indices and maize
response.
The organic wastes used in the first laboratory study included plant materials
(maize. sorghum, kikuyu grass, soybean, red clover residues and acacia
prunings), animal manures (kraal, pasture-fed and feedlot cattle manure, layer
and broiler poultry manure and pig manure), household compost, sewage sludge,
and filter cake. The poultry manure, pig manure and leguminous plant residues
had the highest content of basic cations while sewage sludge had the highest N
content. Poultry manure had very high values for proton consumption capacity,
CaC03 content and ash alkalinity. Proton consumption capacity, ash alkalinity,
total basic cation content and CaC03 content were closely correlated with one·
another. Soil pH was increased and exchangeable AI and total (AIT) and
monomeric (AIMono) AI in solution were decreased by addition of all the organic
wastes: the effect was greater at the higher rate of application. Strong
correlations were recorded between the rise in soil pH and proton consumption
capacity, ash alkalinity, CaC03content and basic cation content of the residues.
The major mechanisms responsible for the elevations in pH were suggested to
be the substantial CaC03content of poultry and pig manures, and filter cake, the
proton consumption capacity of humic material present in household compost
and manures and decarboxylation of organic acid anions during the
decomposition of plant residues and manures. It was proposed that ash alkalinity
is a suitable laboratory test for predicting the potential Iiming effect of organic
residues since it is strongly correlated with the rise in pH that occurs, it is
relatively simple to measure and the values reflect the initial content of organic
acid anions, humic materials and CaC03in the residues. A preliminary field experiment was set up to investigate the effectiveness of kraal
manure as a Iiming material in an acid soil (pHwater =4.1) at a site close to a Zulu
village. The experiment consisted of two rates of lime (L1 = 2.5 and L2 = 5.0 t ha1)
and two rates of kraal manure (K1 = 10 and K2 = 20 t ha-1
) which were
banded and incorporated in a 30 cm wide strip down the plant rows. Treatments
were arranged in a randomized block design with three replicates. A commercial
maize cultivar PAN 6710 and a traditional variety EMBO, used by the farmers in
the locality, were grown. Soils in the plant row were sampled at tasselling and at
harvest. The addition of kraal manure significantly raised soil pH and reduced
concentrations of exchangeable AI and those of both total and monomeric AI in
soil solution. Lime raised pH and the pH continued to increase between tasselling
and harvest. Maize yields for control, kraal manure (K1 and K2) and lime (L1 and
L2) for PAN 6710 were 2.5, 3.7, 5.1, 5.3 and 6.3 t ha-1
; respectively and for
EMBO they were 3.0, 5.4, 5.8, 5.9and 8.2 t ha-1
, respectively. These results
demonstrate the high yield potential of the traditional maize variety under small
scale farming conditions, and show that large yield increases can be obtained by
applying kraal manure.
The long-term effects (24 weeks) of incubation of organic wastes (soybean
residues, poultry, pig and kraal manures and sewage sludge) with an acid soil
were investigated in a laboratory study. After incubation for six weeks incubation,
soil pH was raised and exchangeable AI and Air and AIMono in soil solution were
decreased . by addition of the wastes. Soil pH generally declined and
exchangeable and soluble AI increased over the remainder of the incubation
period. The decline in pH was attributed mainly to nitrification of NH4+ originating
from mineralization of wastes-derived organic N. Addition of organic materials
generally resulted in a decrease in the proportion of solution Air present as
AIMono. That is, the effects of addition of organic materials was two-fold; an
increase in pH in the short term and complexation of AI by organic matter. Since
these effects occur simultaneously, it would be desirable to separate them. For this reason, short-term equilibration experiments (3 days) were conducted to
study the solubility of AI in aqueous solution or in an Oxisol when in equilibrium
,
with 3 manures (kraal, pig and poultry) at pH values of 4.0, 4.5, 5.0, 5.5, 6.0 and
6.5. Addition of manures tended to reduce the concentrations of total AI in
solution (AIT) in the lower pH range (Le. pH 4.0 and 4.5) but increased AIT
concentrations compared to the control, at higher pH values (Le. at pH 5.5 and
above). This was explained in terms of the complexing ability of both the solid
and solution phases. At lower pH, where AI is highly soluble, complexation by
added solid phase manure-organic matter results in a reduction of AI solubility.
However, at high pH, where AI solubility is limited, the most important
mechanism is complexation of AI by soluble organic matter and this increased AI
solubility. Additions of manure reduced the proportion of Air present in
monomeric form (AIMono). This effect was more pronounced in aqueous solution
but was also clearly evident above pH 5.0 in the Oxisol. This reflects the fact that
a large concentration of soluble C in solution can maintain relatively high
concentrations of complexed AI in solution but at the same time maintain low
concentrations of AIMono. It was concluded that formation of AI-organic matter
complexes caused by additions of organic manures can alter the solubility of AI
and reduce the amount of phytotoxic AIMono present in soil solution.
A second field trial was conducted to compare the effects of additions of kraal
manure, grass residues, lime and fertilizer (N-P-K) under field conditions, on soil
pH, AI solubility and maize response and, at the same time follow concomitant
changes in the size and activity of the soil microbial biomass and enzyme
activity. The greatest effects of kraal manure in increasing soil pH and
decreasing AI toxicity were recorded six weeks after planting whereas those of
lime and grass residues were recorded at harvest. Kraal manure and fertilizer
increased significantly AMBIC extractable P and exchangeable K and Zn. In addition, Kraal manure, and to a lesser extent lime significantly increased
exchangeable Ca and Mg.. Soils in the plant row in the grass residue treatments
had the highest microbial biomass C and microbial quotient,followed by kraal
manure, lime and controls. Basal respiration rates and arginine ammonification,
protease, aryl sulphatase, and acid phosphatase activity rates were significantly
increased by addition of all treatments and these increases tended to be
accentuated by fertilizer. Low values for metabolic quotient in the grass residue
treatments were associated with high values for microbial biomass C in these
treatments. The addition of all treatments tended to increase maize yields and, in
general, these yields were greater for the high rate of application of each
amendment. Yields for unfertilized kraal manure were markedly greater than
those for the unfertilized grass residue and lime treatments. This was attributed
to the ability of kraal manure to both increase pH and add nutrients to the soil. / Thesis (Ph.D.)-University of KwaZulu-Natal, Pietermaritzburg, 2004.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/3591 |
| Date | January 2004 |
| Creators | Naramabuye, Fancois-Xavier. |
| Contributors | Haynes, Richard J., Modi, Albert Thembinkosi. |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
| Type | Thesis |
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