The research project critically reviews available literature on nutrient integration between organic amendments and other sources of readily available nutrients. Previous research on nutrient integration has focused solely on compost and inorganic fertiliser as such there is little or no information available about the proposed nutrient integration of compost and STSE. This research aims at filling existing knowledge gaps about compost and sewage effluent integration as a source of plant nutrients and water thereby offering a solution to problems of soil fertility decline and water recycling.
1.2.1 Research aim
The aim of this research is to contribute knowledge towards evaluating optimisation of nutrients in compost and sewage effluent amended soils to meet nutritional requirements of crops for sustainable crop production and environmental protection.
1.2.2 Objectives
To achieve the overall aim of the research project, the following objectives were developed:
i. To determine the mechanism of interaction of nutrient dynamics associated with irrigation of STSE and compost on soils.
ii. To evaluate the effects of final sewage effluent irrigation on soils amended with compost on ryegrass production and leaching of nutrients.
iii. To assess the fate of nutrients and heavy metals in the soil as a result of STSE irrigation on compost amended soils.
iv. To identify the ideal approach to optimising nutrient potential from compost through irrigation with STSE.
The following hypotheses were tested in this research study;
Hypothesis 1
Crop production (dry matter) will be influenced by a unit increase (25%) in the contribution of STSE in integrated compost and STSE nutrient application.
Hypothesis 2
The proportion of STSE in combined application of compost and STSE will be the major determining factor for leaching of nitrate and phosphorous. The readily available nitrate and phosphorous from STSE will be susceptible to leaching.
Hypothesis 3
Accumulation of plant nutrients and heavy metals in the soil profile will be affected by the quantity of STSE in integrated compost and STSE nutrient application.
Hypothesis 4
The optimum compost and STSE nutrient integration will be combinations with less compost (25%) as compared to the contribution of STSE (75%).
1.3 Outline methodology
In order to comprehensively meet the aim and objectives of the research project, the research methodology was sub-divided into 3 categories; (i) incubation experiments (ii) pot (glasshouse) experiment (iii) lysimeter experiment. Each of the experimental units was designed to contribute to the overall aim and objectives of the research. The experiments were designed to be in synergy with each other. Information, knowledge and lessons learnt from one experiment were used in the subsequent experiment.
Incubation study: The incubation study focused on understanding N dynamics, potential N mineralisation and microbial biomass N and C as influenced by the combinations of compost and STSE. This study was conducted under laboratory conditions in an incubator at Cranfield University (Soil Laboratory). This allowed for variables such
temperature and soil moisture to be controlled. Soils were sampled once every 30 days over a period of 120 days and analysed for microbial biomass and soil process rates (N mineralisation).
Glasshouse study: The glasshouse pot experiment was set up in a semi-controlled environment at Cranfield University (Glasshouse facility) to establish the long term role in terms of nutrient provision and the impact on soil chemical properties as a result of STSE irrigation on soils amended with compost. Pots were sown with perennial ryegrass (Lolium perenne) and soils used in the pot experiment were the same soils as used in the incubation experiment. In the first year, soils were sampled after each and every ryegrass cut and at the start and end of the second year. Plant and soil samples were analysed for N and chemical and physical soil properties respectively. This study was also designed to complement the results from the lysimeter study.
Lysimeter study: The lysimeter experiment was set up at Silsoe farm (Cranfield University) to determine the impact of compost and STSE nutrient integration on nutrient accumulation, leaching and N uptake. Leachate was collected periodically and analysed for N and P. Soils were analysed for P and N at the start and end of the experiment. This study augmented the results obtained from the pot (glasshouse) study but focussed on potential impact to the environment through potential leaching (if any).
Figure 1-1 summarises the methodological approach that was followed in the course of
the research. It also shows the linkages between the individual experimental studies and the objectives of the research project.
Figure 1-1 Methodological framework summarising the research approach and the linkage between experiments and objectives.
In the experiments, the main factors under consideration were the combinations of compost and STSE, soil type and N application rates. In all the experiments, two soil types were considered due to their distinct nature; clay loam and sandy loam. Table 1-1 summarise the variables that were tested under each experiment and the underlying experimental factors.
Objective 1
Nutrient dynamics & microbial build up
Objective 4 & 1
Ideal approach & nutrient interaction Objective 3 Nutrient fate and transport Objective 2 Crop production & nutrient leaching Aim
Evaluating nutrient maximisation from compost and sewage effluent amended soils
Incubation I
(N dynamics)
Pot study
Nutrient & irrigation requirement based Lysimeter study Incubation II (Microbial biomass) Research design Information supply
Table 1-1 Summary of the variables tested and the experimental factors under consideration.
Experimental unit Variables tested Experimental factors
Incubation I N mineralisation Soil type
N dynamics N application rates
N kinetics Compost-STSE N combinations
Incubation II Microbial biomass C Soil type Microbial biomass N N application rates Compost-STSE N combinations
Pot study Dry matter (DM)
production
Soil type
N uptake N application rates
N plant Compost-STSE N combinations
Heavy metals - soil
Soil properties
Lysimeter study N & P leaching Compost-STSE N combinations
Soil properties Soil type Dry matter
production TNplant& Nuptake Pplant& Puptake Heavy metals
Repeated ANOVA (General Linear Models) in Statistica 9.0 was conducted on the data to determine significant difference of means. Significantly different levels of treatments were identified using least significant differences at probability of 0.05 (Fishers LSD).
1.4 Thesis structure
Following the introduction presented in this chapter (Chapter 1), Chapter 2 reviews the available information in the literature about composting, its usage in agriculture and wastewater recycling for crop production. It discusses the shortfalls and the knowledge gaps associated with application of either compost amendments or STSE alone in agriculture and the need for nutrient integration. Chapter 3, 4 and 5 details the incubation, pot (glasshouse) and lysimeter experiments respectively.
In each chapter, the associated methodology and major findings are presented respectively. Chapter 6 integrates the findings of Chapters 3, 4 and 5 and discusses practical implications of combining compost and sewage effluent. Chapter 7 reports the overall conclusions of the research and provides ideas for future research.
2 LITERATURE REVIEW
2.1 Introduction
This chapter reviews existing available knowledge on compost recycling to agricultural land, utilisation of recycled water (STSE) and integrated nutrient application in agriculture. This literature review gives a detailed summary of current knowledge regarding the application of STSE and compost to agricultural soil while focusing on benefits and shortfalls of these nutrient sources. A review of knowledge on efforts to improve on the shortfalls of organic amendments has also been outlined with emphasis on integrated organic and inorganic fertiliser nutrient supply.