Thesis (M.S.)--Ohio State University. / Includes bibliographical references (leaves 57-59). Available online via OhioLINK's ETD Center

Thesis (Ph. D. - Economics)--University of Arizona. / Includes bibliographical references.

Thesis (M.Com. (Economics))-University of Pretoria, 2005. / Abstract in English. Includes bibliographical references. Available on the Internet via the World Wide Web.

No description available.

Thesis (M. Eng. (Water Resources Engineering)) -- University of Pretoria, 2008. / Includes bibliographical references (leaves 70-75)

No description available.

Spatial variation of in situ available water content was studied along with related parameters over three 16-ha irrigated fields. The fields, two near Marana (Pima County, Arizona) and one near Casa Grande (Pillai County), range in texture from very fine loam to loamy sand. All soil series present are mapped as Entisols or Aridisols. A 50-m grid provided 56 sampling sites in each field. Each site was sampled at 30, 60, 90, 120 and 150 cm. Samples were collected from each field following a heavy irrigation in March 1977. Bulk samples were collected two days and four weeks after the application of approximately 300 mm of water, to determine in situ water content at field capacity and moisture redistribution with time. Related parameters such as particle size distribution and soil water characteristics were also studied. Bulk density and saturated hydraulic conductivity were determined from undisturbed, core samples. The measured parameters showed different patterns of variation within the same field as well as from one field to the other. Spatial variability of saturated hydraulic conductivity was the highest for which coefficient of variability (CV) ranged upward to 108%. Bulk density, on the other hand, showed the lowest coefficient of variability, as low as 5%. The in situ available water content (AWC), estimated by subtracting moisture content at 15 bars from the corresponding in situ FC values, showed a general tendency to increase with depth corresponding to the increase in percent silt plus sand with depth in all three fields. The coefficient of correlation between the two parameters was high (up to 0.70). The mean values of AWC as estimated using 0.1 bar values for field capacity in the laboratory were consistently higher than the in situ values. The values were within 25 - 35% of each other in Fields 1 and 2, while in the sandier soil of Field 3, the AWC was overestimated by an average of 74% in the laboratory. The CV showed an irregular tendency to increase with depth, but was consistently high in the 150 cm layer in all three fields. Values estimated in the laboratory showed lower CV and higher correlations with soil separates than in situ AWC in all three fields. These two observations can be attributed to the elimination of in situ factors such as texture stratification, compaction, and/or amount of water applied. Agricultural soil formed on water transported material at 0.1 bar were highly correlated with sand (r = -0.8) and the 15 bar values were better correlated with clay (r = 0.5). Also, the coefficient of variability increased consistently with decreases in moisture content. The analysis of variance showed the three fields to be heterogeneous. The variation for within and between the 5 depth groups was significant. A two-way interaction between depths and subareas within each field accounted for 44, 45 and 38% of the total variability in Fields 1, 2, and 3 respectively. Cumulative frequency distribution plots, full normal plots, Kolmogorov-Smirnov tests of goodness-of-fit, tests of skewness and tests of kurtosis were conducted to test the null hypothesis of normal distribution for each parameter. The full normal plots, being sensitive to deviations from normality, rejected the null hypothesis in all cases with few exceptions. They showed the data tends to be skewed to the right and/or kurtic. The alternative frequency distribution of the parameters indicated the data to be asymmetric, short tailed with the exception of percent sand which was symmetric, short tailed for all three fields. A power transformation is suggested as a possibility for transforming the data to get near normal distribution.

Water will become increasingly scarce in the 21st century. Agriculture dominates anthropogenic water use and accounts for about 70% of water withdrawals globally. Unique challenges face tropical small-plot agricultural water management that differs from region to region. This dissertation examines two challenges facing tropical small-plot agriculture. Chapter 2 uses an experimental trial in Western Tanzania to create a unique longitudinal dataset of crop water stress measured over the growing season. The trial tests the effect of seed variety and fertilizer treatment on crop water stress over the growing season and during dry spells. Results demonstrate that hybrid varieties yield significantly more than the locally adapted traditional variety because they are better able to access nutrients and have better stomatal regulation over dry spells. Chapters 3 and 4 shift the focus to India. Chapter 3 characterizes the inter-annual dynamics of anthropogenic water stress across the Central Indian Highlands (CIH), while Chapter 4 examines the hydrological impacts of increasing forest cover on regional water supply and its implications for sustainable irrigation as well as food production. Within Chapter 3, I use extensive data sourced from the Indian government to spatially characterize water demand over the past decade by spatially mapping multiple waves of the Minor Irrigation Scheme Census and Livestock Census collected at the household level, along with monthly power generation datasets. The patio-temporal water demand data is coupled with remotely sensed precipitation and evapotranspiration data to force a customized Sacramento Soil Moisture Accounting Model that computes water supply. Finally, I developed a Groundwater Supply Stress Index to account for the impact of irrigation groundwater withdrawals over the course of the year. Chapter 3 finds that 70% of CIH is water-stressed during some portion of the year and that irrigation makes up approximately 95% of anthropogenic water withdrawals. Chapter 4 extends the findings of chapter 3 in utilizing the infiltration-evapotranspiration trade-off hypothesis to understand the impact of converting croplands to forest on groundwater recharge within the CIH. In this Chapter, I collected and analyzed field data on field-saturated hydraulic conductivity to find that forested land has significantly higher infiltration rates than croplands. These finding are then included in a Spatial Processes in Hydrology model to simulate intra-annual hydrological dynamics of current forest cover versus a forest cover increased to 30% within the river basins of the CIH. Increased forest cover is one of India’s Nationally Determined Commitments at COP21 within the Mission to Green India with a stated aim of improving landscape hydrological functioning. I demonstrate that forest cover increase has the potential to increase groundwater recharge, which could be used to irrigate a second growing season and help offset the loss of cropland through conversion to forest. Collectively, these three chapters harness multiple sources of data and leverage a wide array of innovative methods at multiple scales to shed light on important water management issues faced by small-plot agriculture in the tropics and on opportunities for better agricultural water resource management across two continents.

Thesis (D.Phil(Environmental Economics))--University of Pretoria, 2008. / Includes bibliographical references (leaves 153-162).

Thesis (MScAgric)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The application of water and nutrients via a drip irrigation system influences the water distribution in the soil, soil characteristics and root distribution beneath the dripper. To determine the water distribution pattern beneath a dripper in sandy soil, EnviroSCAN (Sentek) capacitance probes were installed directly below the dripper and at distances of 20, 40 and 60 cm from the dripper. The continuous monitoring of the soil water content (SWC) beneath the dripper provided a good indication of how the water applied through the dripper is distributed in the soil. In this study a semi-impermeable layer in the soil was detected through observing water accumulation patterns in the SWC. Water accumulated above the layer and SWC values increased to far above the upper level of easily available soil water (EAWupper),while the lower soil layers remained drier. The measurements also show that the horizontal water movement is restricted to 20 cm from the dripper. Specific parameters, such as the lower level of easily available soil water (EAWlower),can be used to determine optimal irrigation management. Together with the water distribution study, the root distribution beneath a dripper was also investigated. A high concentration of roots in the area beneath the dripper was found, which corresponds with the area wetted by irrigation. In another study, three irrigationlfertigation methods where investigated to ascertain the influence on soil characteristics and root distribution. These were: micro irrigation (MI) (micro-spinner irrigation with broadcast granular fertilization), conventional drip fertigation (CDF) (daily drip irrigation with daily or weekly fertigation with a unbalanced nutrient solution, containing macronutrients only) and daily drip fertigation (DDF) (daily fertigation of a balanced nutrient solution, containing macro- and micronutrients). The study was conducted in two locations, viz. in the Western Cape Province, on sandy soil, and in the Eastern Cape Province, on silt loam soil. Micro Irrigation: A wide and even root distribution in the entire wetted volume was found on the sandy and silt loam soil. On the sandy soil, the soil pH(KC1)directly beneath the spinner was significantly lower than the pH(KC1)at positions further away from the spinner. Conventional Drip Fertigation: Root studies on sandy soil indicate a poor root development beneath the dripper, with a high concentration of roots in the area between the drippers. The poor root development directly beneath the dipper may be due to oxygen deficiency and/or acidification beneath the dripper. The soil pH(KC1)values show a significant lower pH(KC1)value directly beneath the dripper than further away. In comparison to the sandy soil, the roots developed well beneath a dripper in a silt loam soil. It appears as if soil acidity and/or oxygen deficiency was not a problem on this soil type. The rest of the root system was also well developed. This may be due to this soil's higher water holding capacity which creates a bigger wetted zone. Daily Drip Fertigation: In the sandy soil it seems that the roots developed in a continuous column beneath the dripper line, with little root development further than 20 cm from the dripper line. Where over-irrigation occurred, it caused a poor root development directly beneath the dripper. The root density in this treatment was much higher than in the other two treatments. The use of a balanced nutrient solution and pulse irrigation may be reasons for the better root development. In a silt loam soil a very high concentration of roots was found beneath the dripper and the rest of the root system was also well developed. As with the CDF treatment, it appears as if oxygen deficiency was not a problem on this soil type. / AFRIKAANSE OPSOMMING: Die toediening van water en voedingstowwe deur 'n drip-besproeiings stelsel beïnvloed die waterverspreiding in die grond sowel as die grondeienskappe en wortelverspreiding onder die dripper. Die waterverspreiding onder 'n dripper in 'n sandgrond is bepaal deur EnviroSCAN kapasitansie meetpenne direk onder die dripper en 20, 40 en 60 cm van 'n dripper af te installeer. Die aaneenlopende monitering van die grondwaterinhoud het 'n goeie indikasie van waterverspreiding in die grond gegee. Die horisontale waterbeweging is grootliks beperk tot 'n 20 cm radius vanaf die dripper en die waterbeweging was hoofsaaklik in 'n vertikale rigting. Die teenwoordigheid van 'n semi-deurlaatbare grondlaag in die grondprofiel is opgemerk deur water-akkumulasie in die profiel waar te neem. Wortelverspreiding onder die dripper is ook ondersoek en 'n hoë konsentrasie wortels is in die benatte sone gevind. In 'n verdere studie is drie besproeiings/sproeibemestings behandelings gebruik om die invloed van besproeiing/sproeibemesting op grondeienskappe en wortelverspreiding te ondersoek. Die drie behandelings was: mikro-besproeiing (mikro-besproeiing met korrelbemesting), konvensionele-drip-sproeibemesting (daaglikse drip-besproeiing met daaglikse of weeklikse sproeibemesting van 'n ongebalanseerde, voedingsoplossing wat alleenlik uit makro-elemente bestaan) en daaglikse-drip-sproeibemesting (daaglikse drip-besproeiing met daaglikse sproeibemesting van 'n gebalanseerde voedingsoplossing wat mikro- en makro-elemente bevat). Die studie is in twee areas gedoen, een in die Wes-Kaap, op 'n sandgrond, en die ander in die Oos-Kaap, op 'n slik-leemgrond. Mikro-besproeiing: Die wortelverspreidings studies op die sand- en slik-leemgrond wys op 'n wye en eweredige wortelontwikkeling in die totale benatte volume. Op die sand grond is gevind dat die grond pR(KCl)direk onder die sproeiertjie betekenisvol laer was as die pR(KCl)waardes verder weg van die sproeiertjie. Konvensionele-drip-sproeibemesting: Die wortelverspreiding in die sandgrond wys op geringe wortelontwikkeling direk onder die dripper met die hoogste konsentrasie wortels tussen die drippers. Grondversuring en/of suurstoftekorte onder die dripper kan die oorsaak wees van die swak wortelontwikkeling direk onder die dripper. Die grond pR(KCl)direk onder die dripper was betekenisvol laer as die pR(KCl)verder weg van die dripper. In vergelyking met die sandgrond, het die wortels in die slik-leemgrond goed ontwikkelonder die dripper. Dit wil voorkom of versuring en suurstoftekorte onder die dripper nie 'n probleem was in die slik-leemgrond nie. Die res van die wortelstelsel was ook goed ontwikkel. Dit mag wees weens die grond se hoë waterhoudingsvermoë wat 'n groot benatte area tot gevolg het. Daaglikse-drip-sproeibemesting: In die sand grond wil dit voorkom asof die wortels in 'n aaneenlopende kolom onder die dripperlyn ontwikkel met weinig wortelontwikkeling verder as 20 cm van die dripperlyn. Waar oorbesproeiing 'n probleem was, was daar weinig wortelontwikkeling in 'n klein area direk onder die dripper. Die wortel-digtheid in die behandeling was baie hoër as in die ander behandelings. Die gebruik van 'n gebalanseerde voedingsoplossing en puls-besproeiing mag dalk redes wees vir die beter wortelontwikkeling. In die slik-leemgrond is 'n hoë konsentrasie wortels onder die dripper gevind en die res van die wortelstelsel was ook goed ontwikkel. Soos in die konvensionele-drip-sproeibemesting behandeling wil dit voorkom of suurstoftekort en versuring onder die dripper nie 'n probleem was in die grond nie.