This thesis aims to determine how different organic amendments impact soil aggregate stability and wheat production. Specifically, it seeks to 1) characterize local organic matter sources based on their humic and non-humic substance contents and conversion rates, 2) develop relationships between organic sources and stable aggregate size, and 3) examine differences in water flow, organic carbon content, and wheat yield due to equivalent levels of organic amendments. The results showed that poultry litter had higher levels of active carbon pools while municipal solid waste compost had the highest content of passive humic acid. A field experiment found that municipal solid waste compost most effectively stabilized soil aggregates and improved water flow and wheat yields, due to its high humic acid content.

1. 1
Thesis Title: Enhancing soil aggregate stability and wheat production
through different organic amendments
ABSTRACT
Addition of organic materials for aggregate formation improves the different carbon
pools in soil system. The carbonaceous compounds act as binding agents but they differ in
their impact on stability of aggregates. The aggregate stability varies with the composition
of organic manures and their transformations during decomposition into different carbon
forms. It is hypothesized that an equivalent dose of organic manures will enhance aggregate
stability differently considering that organic sources vary in the contents of humic and non-
humic substances. This study was aimed to (i) determine humic and non-humic substances
content and conversion rate in the local organic matter sources (ii) develop relation between
the organic source and stable aggregate size, and (iii) water flow, organic carbon content
and wheat yield differences due to organic amendments applied on equivalent basis. The
characterization of local organic matter sources (Farmyard manure, Muncipal solid waste
compost and Poultry litter) on the basis of humic and non-humic substances was carried out
by incubating the manures at 30 ± 5 ˚C, and sampling at 30 days interval for six months
duration. The manure samples were analyzed for total organic carbon, microbial biomass
carbon, total polysaccharides, humic acid and fulvic acid contents. The results showed that
organic sources significantly differed in the contents of humic and non-humic substances
and their inter conversion rates. Poultry litter had higher concentrations of microbial

2. 2
biomass carbon and polysaccharide contents (active carbon pools), MSW compost had
highest content of humic acid content (passive carbon). After characterization the effect of
equivalent levels of the organic manures i.e. control, 0.25 %, 0.5 % and 1 % soil organic
carbon on soil physical properties and wheat yield was studied by executing a field
experiment conducted at two different sites viz., Experimental Farm at AAUR and Koont
Research Farm for two years (2012 and 2013), using wheat (CV. Chakwal 50) as a test
crop. Total organic carbon, saturated hydraulic conductivity, dry aggregate size
distribution, wet aggregate stability of soil, grain yield and total biomass yield of wheat
crop were recorded. The aggregate formation and stability of various aggregate size
fractions improved with different sources of carbon. Soil structural stability is dependent on
the composition of organic sources particularly humic acid content. MSW compost
stabilized the soil aggregates significantly due to its highest humic acid content, which
resulted into increased water flow in the soil and improved wheat yield.