Call number: LD2668 .T4 1985 M62 / Master of Science

Differences in cropping practices, including tillage, inputs and crop rotations are the driving factors affecting weed dynamics (weed abundance, composition and crop-weed competition), which can ultimately affect crop yields. Several experiments were carried out to assess the impact of long-term organic and conventional cropping systems on weed abundance, weed community composition, crop yield and yield loss using a long-term (18 year) alternative cropping systems study (ACS) at Scott, Saskatchewan, Canada. The ACS study consisted of three input systems, namely high (conventional tillage), reduced (no-till conventional) and organic input systems and three crop rotation diversities (low diversity, diversified annual grains and diversified annual-perennials). A statistical analysis of the 18-year rotation revealed that the organic rotations have four and seven times higher weed density and 32% and 35% lower crop yields than the reduced and the high input systems respectively. Weed community composition was consistently different in organic rotations compared to the two conventional rotations throughout the years, but year to year random variations were more profound. All cropping systems showed an increase in weed density, weed biomass and crop yields over time, probably due to an increase in rainfall over time. Increasing the crop rotation diversity with annual and perennial crops did not reduce weeds, but decreased crop yields in all systems. A two-year micro-plot experiment with four additional weed competition treatments on the ACS study revealed that the wheat yields were lower in the organic rotations even in the absence of weeds, implying that lower crop yields were due to soil fertility related factors. A greenhouse pot experiment from soils obtained from both organic and reduced rotations revealed that wheat yields were still lower in organic compared to the reduced input systems, even after excess mineral N and P were added. Furthermore, no differences in crop yield loss due to weed competition among cropping systems were identified. Overall, this study revealed that eliminating tillage and reducing inputs are possible without long-term changes in weed abundance, weed community composition or affecting crop yields. However, eliminating synthetic inputs as was done in the form of organic crop rotations resulted in increased weed abundance, changed community composition and decreased crop yields.

Call number: LD2668 .T4 1986 S64 / Master of Science / Animal Sciences and Industry

Call number: LD2668 .T4 1986 S726 / Master of Science / Agronomy

Call number: LD2668 .T4 1986 F73 / Master of Science / Agronomy

Thesis (M.Sc. (Crop Science)) --University of Limpopo, 2012 / Organic tomatoes are increasingly popular with larger market acceptance since organic farming uses limited or no artificial chemicals. Application of organic fertilisers such as cattle manure has potential to boost organic tomato productivity particularly under low input farming systems. However, information is required on the optimum level of manure application on different tomato cultivars to help emerging tomato farmers in South Africa. The objective of this study was to determine the relative response of yield and yield components among selected determinate and indeterminate tomato cultivars using different levels of cattle manure. Two separate field experiments were conducted at the University of Limpopo during 2007 and 2008 using a split plot design with three replications. Two sets of tomato cultivars were included in which one set consisted indeterminate types (Money Maker, Ox Heart and Sweetie) and the other determinates (Roma and Floradade). Cultivars were assigned as the main plot treatments with six rates of manure (0, 10, 20, 30, 40 and 50 in gram per plant) applied as the subplot treatments to each set. Results indicated significant interactions (P ≤ 0.01) between indeterminate tomato cultivars and levels of manure applied for fruit yield and fruit size in both experiments. Plant height showed variation from 78 to168 cm in Experiment I and 87 to 176 cm in Experiment II. During Experiment I fruit number varied from 23 to 91 per plant and 23 to 97 in Experiment II. Significant differences were detected among determinate cultivars on fruit yield varying from 7928 to 3 4705 kg per hectare during Experiment I and 3 169 to 2 9840 kg per hectare during Experiment II. Overall, the best level of manure for maximum fruit yield and greater fruit size was achieved at 40 g per plant in the indeterminate cultivar Sweetie. Conversely, the best level of manure for maximum fruit yield was achieved at 30 g per plant in determinate cultivar Roma. Thus, to achieve maximum yield, tomato growers could apply 600 and 800 kg per hectare manure on the determinate and indeterminate tomato cultivars, respectively. / the National Research Foundation (NRF)

In the arid west large areas of soil contain soluble salts in sufficient concentrations to inhabit crop growth. Of the 1,416,957 acres of soil surveyed in Utah from 1899 to 1920, reported that 43.58 per cent contained 0.2 per cent or more of salts. The management and reclamation of these soils present serious problems. The difficulties are futher accentuated by the fact that many streams used for irrigation contain appreciable quantities of salt. Generally under these conditions removal of the salt from the soil becomes impracticable, and the problem is one of elarning how to get along in spite of the salt. An early study by Lipman and gericke and some preliminary tests at the Utah Agricultural Experiment Station have indicated that crops growing on salty soils may be benefited by applications of copper salts. Because of the economic importance of any procedure for increasing crop production on salty soils, additional studies were proposed to further investigate the problems involved. The research on this problem was planned to investigated the value of copper sulfate in increasing crop yields on salty soils and to study ways in which coppyer might benefit plants under these conditions. Further studies were planned to determine whether an antagonism can be produced in saline soils between sodium cholride and copper sulfate and to determine whether this antagonism is specific for copper or whether it might alos be produced by other ions.

Partial rootzone drying (PRD) is an irrigation management technique designed to reduce water use in grapevines without a decline in yield, thereby increasing water–use efficiency (measured as t/ML) (WUE). The principle of PRD is to keep part of the root system at a constant drying rate to produce soil-derived signals to above–ground plant organs to induce a physiological response. Major PRD effects include a reduced canopy size and greatly increased WUE with possible improvements in fruit quality. Although we have a good understanding of the hormonal physiology of PRD, little is known on the effect of PRD on partitioning of C, N and inorganic ions such as K. This thesis broadens our knowledge on the effects of PRD on grapevine field performance, growth and dry matter accumulation as well as its effects on physiology and biochemistry. In field experiments over 3 seasons, PRD reduced water use in grapevines without a significant decline in yield. PRD effects included reduced shoot growth and greatly increased WUE. Field–grown Cabernet Sauvignon, where the PRD grapevines were irrigated at half the control rate, and Shiraz where the PRD grapevines were irrigated at same rate as controls, confirmed that PRD is not simply an irrigation strategy that applies less water, rather it alters the way in which the plant responds to its environment, e.g. PRD alters the sensitivity of the stomatal response to atmospheric conditions and significantly influence enzymes that regulate nutrient accumulation and partitioning. PRD did not change the total amount of carbon and nitrogen on a whole plant basis. However, it caused a significant partitioning of carbon and nitrogen towards trunk, roots and fruit at the expense of shoot growth. This change in partitioning occurred as a result of altered activity of the enzymes controlling the assimilation of carbon and nitrogen. PRD significantly reduced nitrate reductase (NR) activity in grapevine leaves, which catalyses the first step in the assimilation of nitrate irrespective of the amount of water applied. The reduction in NR activity is correlated with the development of the PRD cycle and the associated reduction in stomatal conductance. PRD also significantly altered grapevine sucrolytic enzyme activity that regulate source:sink relationships. PRD showed transient increases in leaf sucrose phosphate synthase (SPS) activity (formation of sucrose) compared to control, but significantly reduced leaf neutral invertase (sucrose cleavage) and leaf starch content in both field and potted experiments. This may indicate an increased photosynthetic capacity and a reduction in its sink strength for sucrose in favor of organs such as fruit and roots. This hypothesis was reinforced by the fact that berries showed significantly higher levels in glucose and fructose early in the season. Berry sugar content and Brix at harvest however was unaffected. Although PRD had no significant effect on berry characteristics at harvest such as Brix and pH, it occasionally reduced per berry K+ content and increased total amino acid concentration that may lead to positive outcomes for wine quality. PRD–treated grapevine roots on the 'wet'– and 'drying'–sides differed greatly in enzyme activity and osmolality. PRD significantly increased osmolality in both wet and drying roots by increasing total osmolyte concentration that may facilitate the movement of water from wet to dry roots. The increases in osmolality were also associated with increased free polyamine production (spermidine and spermine) in PRD roots that may be related to increased root growth and density. / Thesis (Ph.D.)--School of Agriculture and Wine, 2005.

Detecting stress in plants resulting from different stressors including nitrogen deficiency, salinity, moisture, contamination and diseases, is crucial in crop production. In the Nile Valley, crop production is hindered perhaps more fundamentally by issues of water supply and salinity. Predicting stress in crops by conventional methods is tedious, laborious and costly and is perhaps unreliable in providing a spatial context of stress patterns. Accurate and quick monitoring techniques for crop status to detect stress in crops at early growth stages are needed to maximize crop productivity. In this context, remotely sensed data may provide a useful tool in precision farming. This research aims to evaluate the role of in situ hyperspectral and high spatial resolution satellite remote sensing data to detect stress in wheat and maize crops and assess whether moisture induced stress can be distinguished from salinity induced stress spectrally. A series of five greenhouse based experiments on wheat and maize were undertaken subjecting both crops to a range of salinity and moisture stress levels. Spectroradiometry measurements were collected at different growth stages of each crop to assess the relationship between crop biophysical and biochemical properties and reflectance measurements from plant canopies. Additionally, high spatial resolution satellite images including two QuickBird, one ASTER and two SPOT HRV were acquired in south-west Alexandria, Egypt to assess the potential of high spectral and spatial resolution satellite imagery to detect stress in wheat and maize at local and regional scales. Two field work visits were conducted in Egypt to collect ground reference data and coupled with Hyperion imagery acquisition, during winter and summer seasons of 2007 in March (8-30: wheat) and July (12-17: maize). Despite efforts, Hyperion imagery was not acquired due to factors out with the control of this research. Strong significant correlations between crop properties and different vegetation indices derived from both ground based and satellite platforms were observed. RDVI showed a sensitive index to different wheat properties (r > 0.90 with different biophysical properties). In maize, GNDVIbr and Cgreen had strong significant correlations with maize biophysical properties (r > 0.80). PCA showed the possibility to distinguish between moisture and salinity induced stress at the grain filling stages. The results further showed that a combined approach of high (2-5 m) and moderate (15-20) spatial resolution satellite imagery can provide a better mechanistic interpretation of the distribution and sources of stress, despite the typical small size of fields (20-50 m scale). QuickBird imagery successfully detects stress within field and local scales, whereas SPOT HRV imagery is useful in detecting stress at a regional scale, and therefore, can be a robust tool in identifying issues of crop management at a regional scale. Due to the limited spectral capabilities of high spatial resolution images, distinguishing different sources of stress is not directly possible, and therefore, hyperspectral satellite imagery (e.g. Hyperion or HyspIRI) is required to distinguish between moisture and salinity induced stress. It is evident from the results that remotely sensed data acquired by both in situ hyperspectral and high spatial resolution satellite remote sensing can be used as a useful tool in precision farming in the Nile Valley, Egypt. A combined approach of using reliable high spatial and spectral satellite remote sensing data could provide better insight about stress at local and regional scales. Using this technique as a precision farming and management tool will lead to improved crop productivity by limiting stress and consequently provide a valuable tool in combating issues of food supply at a time of rapid population growth.

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