Dryland maize and irrigated maize/oats rotation

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GENERAL INTRODUCTION

Beneficial use of sewage sludge on agricultural lands is a very well known practice around the world. The benefits include; a source of essential crop nutrients (Muse et al., 1991), improvements in soil structure (Ojeda et al., 2007), and minimisation of soil erosion and runoff (Muse et al., 1991; Ojeda et al., 2003). Nutrients applied above a crop’s nutrient requirement, however, can be detrimental to plant growth (Brady, 1974) and will ultimately pollute water bodies (Neal et al., 2002). In addition, waste products from cities and industrial areas contain pathogens, toxic elements and organic contaminants which can pose a serious health hazard. Therefore, many countries have developed sewage sludge guidelines to optimize agricultural benefits without compromising sustainability.

Dryland pasture (Weeping lovegrass)

1. Sludge application above the 8 Mg ha-1 yr-1 limit will increase weeping lovegrass hay yield, crude protein content, and water use efficiency. 2. The ideal sludge application rate to satisfy weeping lovegrass N demand is dynamic and could exceed the 8 Mg ha-1yr-1 sludge limit. 3. Under high hay yield productin conditions, N supply from double the norm can fully be utilized and such systems are not prone to excessive nitrate leaching. 4. Sludge application according to crop N demand results in the accumulation of total and plant available P in the soil profile.

Turfgrass

1. High sludge surface loading rates well above recommendations based on crop removal
a. Are possible without reducing turf growth and quality.
b. Do not cause an accumulation of N and P below the active root zone.
c. Can minimize soil loss through sod harvesting, and
d. Do not cause unacceptably high nitrate and salt leaching.

Background information

Population growth in cities and the expansion of industries is resulting in a rapid increase in the volume of waste products that need to be either beneficially used or disposed of in some way. Similar to other countries, South African wastewater treatment plants are under enormous pressure to dispose of or utilize their sludges and effluents in environmentally sustainable ways. The daily total wastewater flow emanating from South African wastewater treatment plants was estimated at 5400 Ml d-1(Marx et al., 2004). Considering the potential benefits of using sludge on agricultural lands, South Africa, like all other countries, have developed sewage sludge guidelines for beneficial agricultural use (WATER RESEARCH COMMISSION, 1997; Snyman and Herselman, 2006). Despite this, only 28% of the total South African sludge is used for beneficial agricultural purposes.

ACKNOWLEDGEMENTS
ABSTRACT
CHAPTER 1 GENERAL INTRODUCTION
CHAPTER 2 LITERATURE REVIEW
2.1 Background information
2.2Sewage sludge types, characteristics, and agricultural use
2.2.1 Sewage sludge types
2.2.2 Nitrogen and sewage sludge
2.2.3 Phosphorus and sewage sludge
2.2.4 Utilising sewage sludge on agricultural lands
2.2.5 Sludge application rates on agricultural lands
2.2.6 Classification of sludge for use on agricultural lands
2.2.7 Experiences with sewage sludge on cropping systems
2.3 Nitrogen modelling
2.3.1 Mineralization
2.3.2 Immobilization
2.3.3 Nitrification
2.3.4 Denitrification
2.3.5 Ammonia volatilization
2.3.6 Crop nitrogen uptake
2.4 Motivation for this study
REFERENCES
CHAPTER 3 MATERIALS AND METHODS
3.1 Field site description
3.2 Sludge characteristics
3.3 Field trial and treatments
3.3.1 Dryland maize and irrigated maize/oats rotation
3.3.2 Weeping lovegrass (Eragrostis curvula)
3.3.3 Turfgrass (Kikuyu, Pennisetum clandestinum Hochstex Chiov.)
3.4 Rainfall and irrigation
3.4.1 Rainfall
3.4.2 Irrigation
3.5 Soil solution sampling and analyses
3.6 Plant sampling
3.6.1 Dryland and irrigated maize
3.6.2 Irrigated oats
3.6.3 Weeping lovegrass
3.6.4 Turfgrass
3.7 Soil sampling
3.7.1 Dryland maize and irrigated maize/oats rotation
3.7.2 Dryland pasture
3.7.3 Turfgrass
3.8 Plant and soil chemical analyses
3.9 Additional methods involved in turfgrass trial
3.9.1 Mowing and sod harvest
3.9.2 Soil loss through sod lifting
3.9.3 Turfgrass establishment rate
3.10 Model parameter description
3.10.1 Crop growth model
3.10.2 Nitrogen model
3.11 Statistical analyses
REFERENCES
CHAPTER 4 AGRONOMIC CROPS
4.1 Grain and forage yield
4.1.1 Grain yield
4.1.2 Forage yield
4.2 Crop N uptake
4.2.1 Grain N uptake
4.2.2 Forage N uptake
4.3 Soil profile total N mass balance, residual nitrate and ammonium, and nitrate leaching
4.3.1 Total N mass balance
4.3.2Residual nitrate
4.3.3 Residual ammonium
4.3.4 Nitrate leaching
4.4 Total P mass balance and residual Bray-1P
4.4.1 Total P mass balance
4.4.2 Soil profile residual Bray-1 extractable P
4.5 Conclusions
REFERENCES
CHAPTER 5 PERENNIAL DRYLAND PASTURE – WEEPING LOVEGRASS (Eragrostis curvula L.)
5.1 Hay yield, crude protein content, and water use efficiency
5.1.1 Hay yield
5.1.2 Crude protein content
5.1.3 Effect of sludge application rate on rainfall use efficiency
5.2 Hay N uptake
5.3 Soil profile total N mass balance, nitrate leaching, residual nitrate and ammonium
5.3.1 Total N mass balance
5.3.2 Residual nitrate and nitrate leaching
5.3.3 Residual ammonium
5.4 Total P mass balance and residual Bray-1P
5.4.1 Total P mass balance
5.4.2 Soil profile residual Bray-1 extractable P
5.5 Conclusions
REFERENCES
CHAPTER 6 TURFGRASS
6.1 Turfgrass growth and quality
6.1.1 Establishment rate
6.1.2 Turfgrass colour
6.1.3 Sod integrity
6.2 Accumulation of N and P in soil below active root zone
6.2.1 Nitrogen
6.2.2 Phosphorus
6.3 Soil loss through sod harvesting
6.4 Nitrate and salt leaching
6.4.1 Nitrate leaching
6.4.2Salt leaching
6.5 Conclusions
REFERENCES
CHAPTER 7 NITROGEN MODELLING
7.1 Model calibration
7.2 Model corroboration
7.2.1 Agronomic crops
7.2.2 Weeping lovegrass
7.3 Conclusions
CHAPTER 8 CONCLUSIONS