In a study to investigate the fate of the applied P in soils, a red-sandy clayey soil (Ferric Luvisols) from Rustenburg (high P fixing) and a red-sandy loam soil (Ferric Acrisols) from Loskop (low P fixing) were used. Sequential P fractionations were used to determine the content of the different P pools to show which pool the applied P was transformed to. The soils treatments consisted of different Prates (0, 25, 50, 100, 150, and 200 mg kg-1), and incubation periods (1, 60, 120, 180, and 240 days) under a laboratory conditions. The sequential P fractionation procedure consisted of extraction with hydrous ferric oxide in a dialysis membrane tube (DMT-HFO), 0.5M NaHC03, O.1M NaOH-P, 1.0M HCI, concentrated HCI, and concentrated H2S04 + H2O2. Approximately 30 to 60 % of the added P were transformed into less labile P pools within one day and 80-90 % after 60 days. This transformation was faster in the Rustenburg than in the Loskop soil showing a higher P fixation capacity. A major part of the P transformation was to the -OH-P1 pool with a recovery of about 30%. In the second experiment an attempt was made to determine P desorption rates by successive DMT-HFO extractions (1, 7, 14, 28, and 56 days) after the transformations of the applied P. This was followed by the sequential extractions to determine the changes and distribution of the added P into different P pools as well as which pools the P was des orbed from. The Rustenburg and Loskop soils were treated to different Prates (0, 25, 50, 100, and 200 mg P kg-1) and incubation periods (1, 120, and 240 days). The cumulative DMT -HFO extraction curves for 56 days showed that desorption could continue for a much longer period. This property is important in the economical management of fertilizer applications rates. Results showed the transformations and distribution of the applied P during incubation periods and proved that all the stable soil P pools contributed to the labile P pool by different proportions after prolonged successive DMT-HFO extractions. Although Rustenburg soil is considered a high P fixing soil, the P release rates under laboratory conditions were high enough to meet the requirements of cotton and tobacco crops. Root systems of these crops do not exploit 100 % soil volume as this laboratory method, which could explain why these crops experience P deficiencies. It is envisage that by using this method the P releasing properties of a soil could be used to develop a P desorption model to determine how much extractable P, with a specific extractant, in a particular soil, should be available at the beginning of a growing season to sustain a high enough P releasing rate to meet the requirements of a certain crop up to the end of the growing season. To do this, a model to describe root development that represents the percentage of the soil exploited P desorption rates that simulate P uptake by plant roots will be necessary. / Thesis (DPhil (Plant Production: Horticulture))--University of Pretoria, 2006. / Plant Production and Soil Science / unrestricted

Recent investigations have shown that application of appropriate concentrations of naphthenate induces greater growth and yield of several crop plants. However, reports are lacking on the effect of naphthenate on plants grown under various temperature and light conditions and also on physiological and biochemical changes induced in bush bean (Phaseolus vulgaris L.Var. Top Crop) plants following naphthenate treatment. In the course of the present work the following aspects were investigated: 1) juvenile growth, as measured by fresh and dry weight of roots, stem and leaves, number and area of leaflets and plant height; 2) reproductive growth, as measured by flower number, number and fresh weight of pods, and number and weight of dry seeds; 3) chemical composition, such as moisture content of roots, stem, leaves, and pods, chlorophyll and carotenoid content of leaves, ascorbic acid content of green pods and loss of ascorbic acid by pods during storage for five days, and 4) such physiological and metabolic changes as rates of apparent photosynthesis and dark respiration, activities of the enzymes nitrate reductase, glutamic-pyruvic transaminase, phosphorylase and phosphoglyceryl kinase. Subsequent to KNap treatment, plants in some experiments were grown in growth rooms provided with 26°/26°, 26°/21° and 15°/15°C, day/night temperature. At 26°/26° and 15°/15° plants were grown under three different light intensities, 1500, 1000 and 500 ft-c. The results revealed that: (1) treatment with KNap resulted in increases in plant height, number and area of leaflets, fresh and dry weight of roots, stem and leaves, and total chlorophyll content in leaves; (2) measurements made with intact plants using an infrared CO₂ analyzer revealed increases in rates of apparent photosynthesis and dark respiration in treated plants; (3) the activity of the four enzymes mentioned was stimulated in plants treated with KNap; (4) increases in number and fresh weight of green pods, number and weight of seed were observed in treated plants; (5) treatment resulted in higher ascorbic acid content in green pods at harvest and the treatment had a protective action on ascorbic acid loss during storage. Different plant organs were found to respond differently to treatment depending on temperature and light intensity in which the plants were grown. The maximum relative stimulatory effect of KNap treatment was found mostly at 26°/21° and it was followed by 26°/26° and 15°/15°, in plants grown under a light intensity of 1500 ft-c. Plants grown at 26°/26° showed maximum relative stimulation in most instances in high light. The maximum relative stimulation for plants grown at 15°/15° was in medium light generally speaking. In proposing a physiological and biochemical basis for the stimulation of growth and yield following KNap treatment, the following points may be emphasized: (a) the stimulated rate of photosynthesis produced a larger amount of photosynthate which could be utilized in the biosynthesis of all cell constituents and serve as substrate for respiration and other chemical processes; (b) the stimulated rate of respiration and activity of phosphoglyceryl kinase resulted in an increased supply of available energy, as ATP and reduced nucleotides, for biosynthesis; (c) the augmented supply of amino acids resulting from the greater activity of nitrate reductase and transaminase would be favorable for enhanced synthesis of protein, evident in stimulated growth. / Science, Faculty of / Botany, Department of / Graduate

In 1987, a research project, conducted in the interior of British Columbia, was undertaken in order to obtain preliminary fertilization response data for three interior species. In 1988, as part of this contract, 12 screening trials were established in young interior spruce stands in the north-central interior of B. C. using factorial combinations of nitrogen and "complete" mix fertilizer. Initial assessment of the unfertilized foliage obtained from the 12 installations indicated that all stands exibited low nitrogen and potentially low sulphur levels. After fertilization, the effects of the treatments were measured by needle weight response, nutrient concentration, and subsequent nutrient content response. In all 12 installations the largest needle weight response occured when the nitrogen and the "complete" mix fertilizers were combined.. In the treatments where nitrogen was applied alone, no significant change in needle size was recorded. Nutritionally, nitrogen fertilization resulted in large increases in nitrogen concentration, indicating this element was limiting. As well, nitrogen fertilization also produced large decreases in K, S, and S04-S concentrations. Nitrogen-only fertilization also caused large elevations in the N/S ratios to occur. This elevation in N/S ratios and the subsequent decreases in S and S04-S concentrations seem to indicate that nitrogen-only fertilization has a negative impact on the sulphur nutrition of interior spruce. The addition of the "complete" mix fertilizer was, in most cases, successful in returning the decreased nutrient concentration levels of K, S, and S04 and the elevated N/S ratios back to their original unfertilized status. From these results it appears that nitrogen fertilization of interior spruce should only be considered if it is accompanied by a mixture of other nutrients; the most important component being sulphur. / Forestry, Faculty of / Graduate

A two year field study located in Delta Municipality, British Columbia, was conducted to investigate the possible improvement of nitrogen (N) fertilizer recommendations for arable crops in the Lower Fraser Valley (LFV). After reviewing current N fertilizer recommendation systems in other humid regions, the approach taken in the study was to determine the applicability of a spring soil test and/or a N Index system for the LFV region. The project, which used sweet corn (Zea Mays saccharata) as the trial crop, consisted of two interconnected parts: 1) A 'Replicated Fertilizer Response Trial' which aimed to; a) Monitor soil N0₃-N and NH₄-N during spring to a depth of 80cm, using intervals of 0-20, 20-50, and 50-80cm. b) Investigate yield response and N uptake efficiency at four different rates of sidedress applied urea, 0, 50, 100 and 200 kg ha⁻¹ N. c) Compare the effectiveness of urea applied broadcast preplant, and applied by sidedressing, when the crop was approximately 30cm tall. 2) A 'Multifarm Survey' at 28 locations, comparing plots sidedressed with 135 kg ha⁻¹ N, to control plots containing only starter N. The aim of this survey vas to establish the range of N supplying capacities in some LFV soils and relate these capacities to other soil properties and site history. Monitoring mineral N in the soil demonstrated that soil N0₃-N increased during the spring, reaching a peak 5-6 weeks after planting. Maximum N0₃-N levels in the 0-80cm profile were 90 and 135 kg ha⁻¹ in 1984 and 1985 respectively. NH₄-N levels tended to be low compared to NO₃-N. As a proportion of total mineral N, NH₄-N decreased from approximately 25% at the beginning of May, to between 10 and 15% by mid June. Large amounts of spatial and temporal variability in both N0₃-N and NH₄-N were observed on the two sites studied. The difference in magnitude of mineral N between the years was due to a large number of site and weather factors which could not be separated. No significant differences in corn yield or crop N content were found between any of the four fertilizer treatments in the Replicated Response Trial. Similarly, no significant differences were found in the comparison of urea N applied by broadcasting before planting and urea N applied by sidedressing. Two reasons for this lack of response were suggested, one, that the soil plus starter N provided sufficient N for the crop's needs, and two, that the fertilizing techniques were inefficient considering the soil and weather conditions. The Multifarm Survey provided the greatest amount of information relevant to the project's objectives. It showed that the range of soil types and cropping regimes on corn fields in Delta Municipality was too narrow to have a direct influence on N supplied by the soil. Soil N supplying capacity was shown to be weakly related to organic matter, the study results suggested that a knowledge of site history was necessary before this relationship could be assumed to be positive. Such findings favoured the implementation of a spring soil test rather than a N Index system. Various approaches to estimating N fertilizer requirements using a spring soil sample were examined. In conclusion, the project showed that substantial amounts of N vere made available by the soil and that these should be taken into consideration when fertilizer recommendations are made. The study suggested that in a small agricultural region such as Delta Municipality, spring soil N0₃-N appeared to be sufficiently well correlated with total soil plus crop nitrogen to warrant the further investigation of a soil test for N. This test, for corn, should be as close as possible to sidedress time and the ideal sampling depth would be to 80cm. Anomalous sites with adverse soil conditions, such as poor drainage, marine influences, low pH or compaction should not be included in the test. / Land and Food Systems, Faculty of / Graduate

Nitrogen fertilizers are extensively used to enhance the growth of biomass crops. This study was conducted to determine the effect of N rates on the biomass yield and quality, and N uptake of several crops. The experiment was conducted at Fargo and Prosper, ND, in 2010 and 2011. The crops studied were forage sweet sorghum [Sorghum bicolor L. Moench], sorghum x sudangrass [Sorghum bicolor var. sudanense (Piper) Stapf.], kenaf [Hibiscus cannabinus L.], and reed canarygrass [Phalaris arundinacea L.]. The different crops constituted the main plots and the nitrogen rates were regarded as subplots. The five N rates were 0, 75, 100, 150, and 200 kg N ha-1. Forage sweet sorghum and sorghum x sudangrass had the greatest dry matter biomass yield. Nitrogen fertilization increased biomass yield for each of the crops. The results indicate that forage sorghum and sorghum x sudangrass have the greatest potential as a feedstock.

No description available.

No description available.

No description available.

No description available.

No description available.