CTAHR Ph.D Dissertations
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ItemRelease of non-exchangeable potassium in Hawaiian sugar cane soil(University of Hawaii, Honolulu, 1949-06)
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ItemDesorption of adsorbed ametryn and diuron from soils and soil components in relation to rates, mechanisms, and energy of adsorption reactions( 1976)This study was designed to examine in detail the causes of hysteresis (irreversibility) in the adsorption-desorption process' for two herbicides and its impact under field conditions. An effort was made to relate rate, mechanism and energy of adsorption to this phenomenon. Adsorbents employed in this study were four soils which differed greatly in mineralogy and organic matter content, and two clay minerals, montmorillonite and kaolinite. Adsorption was measured by the batch (slurry) method, supplemented by a flow technique when necessary. Adsorption and desorption equilibrium times for each adsorbate and adsorbent combination were determined and the rate of adsorption was related to hysteresis. Desorption was generally slower than adsorption and both took comparatively longer times in the case of Kaipoioi soil (high in organic matter). Both adsorption and desorption proceeded rapidly during the first few hours and slowed down as the equilibrium time was approached. The faster adsorption equilibrium of ametryn was achieved, the larger was the hysteresis. This kind of relationship was absent in the case of diuron. The magnitude of hysteresis increased with the magnitude of adsorption (as expressed by the Freundlich adsorption constant, Kf) for the various systems. The Freundlich constant, l/n, did not exhibit any correlation with hysteresis. It was, however, observed that the constant increased with temperature and its values were relatively higher in the case of montmorillonite clay and Panoche soil (for which montmorillonite is the dominant clay mineral and organic matter is very low). Adsorption mechanisms appeared" to be related to hysteresis. The hysteresis was larger where ionic attraction was the adsorption mechanism (when ametryn is protonated at low pH) than where mainly physical forces were operative. Diuron exhibited more hysteresis with hydrophobic adsorption (on soils with high organic matter) than with the "water bridge" mechanism (on clay minerals and soils with very low organic matter content). Regardless of adsorption mechanisms, some of the adsorbate molecules were held strongly by the adsorbents, giving rise to hysteresis. Thermodynamic parameters were calculated from equilibrium adsorption measurements and were related to the observed hysteresis. In general, the higher the hysteresis, the larger was, the absolute value of the standard free energy change. The absolute values of standard enthalpy and entropy had a tendency to increase with an increase in magnitude of hysteresis. It can be deduced that the more negative the values of standard free energy change, the greater is the bonding strength, and thus the standard free energy change is related to adsorption mechanism. In the field-watershed portion of this study, the largest diuron concentrations in runoff water were found during the initial storms following herbicide application. After about one year the level of the chemical dropped to a few parts per billion and was almost constant thereafter. The bulk of pesticide was carried by runoff water rather than by suspended soil. The concentration of diuron in runoff was dependent on the concentration of the chemical in the soil. Laboratory adsorption-desorption measurements showed hysteresis in the adsorption-desorption process, which probably attenuated downward movement of the herbicide and contributed to its long persistence in the soil. Recently adsorbed diuron was released to a greater extent than residual diuron. Laboratory measurements assisted in predicting pesticide behavior in the field.
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ItemStudies on the biology of sourgrass (Trichachne insularis (L.) Nees) and of its competition with buffelgrass (Cenchrus ciliaris L.) and guineagrass (Panicum maximum Jacq.)( 1975)Sourgrass (Trichachne insularis (L.) Nees) is one of the most serious pasture weeds in Hawaii. It has ruined many good dryland pastures on Maui, Molokai, and Oahu. Studies were conducted on its distribution, seed germination, seedling emergence and growth and development under natural and controlled conditions and on its competition with the improved pasture species, buffelgrass (Cenchrus ciliaris L.) and guineagrass (Panicum maximum Jacq.). Field surveys showed that sourgrass was most abundant below 540 meters elevation, in dry zones of 120 to 760 mm of annual rainfall. Sourgrass occurred on hillsides or on gentle basal slopes where Prosopis pallida (Humb. and Bonpl. ex Willd) HBK. or Leucaena latisiliqua (L.) Gillis and Stearn grew. Distribution of sourgrass corresponded to shade conditions. The soils of infested areas were commonly silt clay to silt clay loam with shallow soil profiles. Low rainfall, high temperatures, and shade were the more important factors in the distribution of sourgrass. Optimum germination of sourgrass seed was obtained under light with alternating temperatures of 20-30 C or 25-35 C or with constant 30 C. Germination in complete darkness was very poor at most temperatures. Germination of sourgrass seed was best under 8 or 12 hour photoperiod but was reduced under 16 and 24 hour photoperiods. Gibberellic acid, kinetin, and thiourea were effective in enhancing germination at 22 C in the dark. Germination percentages of sourgrass, buffelgrass, and guineagrass decreased as moisture stress simulated with mannitol was increased. Guineagrass and buffelgrass were more affected by moisture tension than was sourgrass. The capacity of sourgrass to germinate rapidly under low soil moisture could give it a competitive advantage over buffelgrass and guineagrass under semi-arid to arid conditions. Sourgrass seedling emergence was greatest from seeds planted near the surface and decreased as the depth of planting increased. Sourgrass was capable of emerging from a maximum depth of 5 cm in the clay loam used in this study. Plant height, dry weight, tillers per plant, and seed yield per plant were greatly decreased as the plant density was increased from 5 plants to 160 plants per pot. Intraspecific competition was probably a major factor affecting seedling development and survival of sourgrass. Sourgrass flowering was found to be day-neutral in response to photoperiod. The plants under longer photoperiods flowered earlier than those grown under shorter photoperiods probably because floral development was slow in response to insufficient light energy under shorter photoperiods. Plant height and dry matter production of shoots of sourgrass, buffelgrass, and guineagrass increased but dry weight of roots and tillers per plant decreased with increasing shade. In addition, flowering was delayed as shade increased. Nitrogen fertilization increased plant height, dry weights of shoots and roots, and tillers per plant for all species. A pot study was conducted to evaluate the competitive ability of sourgrass, buffelgrass, and guineagrass under different levels of shade and nitrogen fertilization. The growth of sourgrass was severely suppressed when grown with buffelgrass, guineagrass or both. Highly significant reductions in height, dry weight, and tillers per plant of sourgrass resulted from competition with associated grass species. Sourgrass was thus less competitive than buffe1grass and guineagrass. It is evident from these results that sourgrass in pastures can be controlled through competition from buffelgrass and guineagrass under proper management of grazing and fertilization. Practices which would enhance the competitive advantage of buffe1grass and guineagrass over sourgrass would include the following: (1) ensuring adequate moisture for germination, (2) fertilization, and (3) prevention of over-grazing.
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ItemWeed ecology and economic importance of Emilia javanica (Burm.) Rob. and E. sonchifolia (L.) DC( 1975)The Emilia species and types in Hawaii were studied with respect to their taxonomy and life history, importance as disease reservoirs for the tomato spotted wilt virus, and as a weed competitor with crop plants like lettuce (Lactuca sativa L.), mustard cabbage (Brassica juncea Czern. & Coss.), sweet corn (Zea mays L.) and transplanted tomato (Lycopersicon escu1entum L.). Of the four Emilia species reported in Hawaii, only E. javanica (Burm.) Rob. and E. sonchifolia (L.) DC were found on the islands of Oahu and Kauai, while on Lanai only the Red and Orange types of E. javanica were observed. The E. javanica type Purple was found only in limited areas on Oahu and Kauai. The E. javanica types, particularly the Red type, which were referred to as E. sonchifo1ia or E. sagittata (Vahl) DC by other workers, are the most predominant types on Oahu, Kauai and Lanai. The similarities in vegetative and floral morphology of the different color types of E. javanica, in addition to their ability to interbreed indicate that they belong to the same species. Plant height, capitulum size, number of achenes (seeds) per capitulum, number of capitula per plant were influenced by fertilizer and shading •treatments. The E. javanica types were taller (50 to 62 cm) than E. sonchifolia (19 to 30 cm) at flowering. Fertilized Emilias under 55% shade were tallest while unfertilized plants under full sunlight were shortest. The total length of the capitulum of the E. javanica types ranged from 12.5 to 13 mm compared to E. sonchifolia with 10.5 to 11 rom. When fertilized with N-P-K and grown in full sun-light, the Orange, Red and Purple types of E. javanica had 70, 64 and 57 seeds per capitulum, respectively, while E. sonchifolia had 60. Among the Emilias, the E. javanica type Purple produced the greatest number of capitula per plant. The earliest to mature (seed to seed) was the Purple type of E. javanica (48 ± 2 days), followed by the Red (51 + 1 days), Orange (52 + 1 days), and E. sonchifolia (53 + 3 days) was the latest. Seed germination studies showed that seeds of E. javanica matured earlier than E. sonchifolia. However, viable seeds were formed in both species before the capitula were ready to dehisce. All Emilias examined produced both light and dark colored seeds. The seeds of the Emilia species and types required light for germination up to a period of 4 weeks after harvest. Germination and dormancy varied with seed color, species, and types. Newly harvested seeds of E. sonchifolia germinated better under a wider temperature regime (15 to 35 C) than the E. javanica types (25 to 35 C). Flowering response of the Emilia species and types were day neutral with respect to photoperiod. Observed differences in the time of flowering were due to differential rates of inflorescence development than to differential initiation of the floral primordium. Plants grew taller as the photoperiod was lengthened. Transmission studies by sap inoculation of the tomato spotted wilt virus (TSWV) showed that all the types of ~. javanica (Orange, Red and Purple) and ~. sonchifolia harbored and transmitted the TSWV to tomato 'Tropic' and lettuce 'Anuenue'. The two species of Emilia differed with respect to infection with TSWV. E. sonchifolia gave a lethal reaction while the E. javanica types tolerated infection of the virus. The TSWV from tomato and lettuce were re-transmitted back to the Emilias. Pure stands of E. javanica type Red grown at specific densities with lettuce 'Anuenue', mustard cabbage 'Waianae', sweet corn 'H-68', and transplanted tomato 'N-52' demonstrated that the effects of Emilia on crop growth and yield varied with crop species. For example, full season competition of Emilia at 11 weeds per crop plant decreased the dry weights of lettuce and mustard cabbage by 70 to 30%, respectively. Sweet corn fodder was not affected even with 150 weeds per crop plant, while transplanted tomato fruit yield was reduced 18% by 80 to 126 weeds per crop plant. Because non-limiting irrigation was supplied, differences in response to Emilia competition depended on the crop plant's ability to compete for light and nutrients.
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ItemInteractions between phosphate adsorption and cation adsorption by soils and implications for plant nutrition( 1974)Interactions between phosphate adsorption and cation adsorption were studied in four Hawaiian soils. These belonged to the following soil groups: Hydrandept, Gibbsihumox, Eutrustox and Haplustoll. Relevant ion adsorption mechanisms were investigated by electrochemical techniques and direct adsorption measurements by means of adsorption isotherms. Implications for the availability of P, Ca, Mg and K for plants were investigated in pot experiments. Interactions between phosphate adsorption and cation adsorption were important in highly weathered soils containing mainly variable charge clay minerals such as Fe and Al hydrous oxides. These soils could be characterized by their zero point of charge (ZPC). The ZPC will increase with increasing contents of oxidic colloids. Consequently the adsorption of anions, particularly phosphate, will increase. For the soils in this study ZPC and P adsorption decreased in the following order: Hydrandept > Gibbsihumox > Eutrustox > Haplustoll Calcium was adsorbed specifically by the hydrous oxides present in the highly weathered soils, especially the Hydrandept and Gibbsihumox. The ZPC value of oxidic soils therefore should be determined in CaCl2 solutions to prevent the interference from adsorbed Ca in soil samples. This interference did affect ZPC measurements with NaCl or Na2SO4 as supporting electrolytes since the non-specifically adsorbed Na ion does not compete with Ca adsorbed in the Stern layer. Consequently no ZPC was determined but an isoelectric point (IEP) which refers to the charge o at a distance of several A units away from the colloid surface. A similar problem applied to the extraction of exchangeable Ca by NH40Ac. Non-specifically adsorbed NH4+ ions did not compete effectively with specifically adsorbed Ca, causing incomplete Ca extraction from these soils. With decreasing ZPC values cation adsorption became relatively more important than anion adsorption. Consequently, adsorbed phosphate, which lowered the ZPC, was associated also with increased cation adsorption. The adsorption of 700 ppm P by the Gibbsihumox lowered the ZPC of that soil from 4.10 to 3.85 and increased the cation adsorption by 1.35 me/100g soil at pH 5.5. This amounts to 0.6 me/mmol P adsorbed/ 100g soil. The increase in cation adsorption was more pronounced for specifically adsorbed divalent cations than for non-specifically adsorbed monovalent cations. Because of specific Ca adsorption, applications of NH 4 phosphates had greater effects on the adsorption of other cations (Na, K, NH4 , Mg, Ca) than had Ca phosphates. Hence if all P in these highly weathered soils was applied as Na(or NH4) phosphates, deficiencies of Mg, Ca and certain trace elements could be induced. In addition dispersion of inorganic and organic fractions occurred in the Gibbsihumox. Phosphate solubility in the oxidic soils depended mostly on salt concentration and cation valency. It was decreased by the accompanying cation according to a lyotropic series: K < Mg ≤Ca. This cation effect on P solubility decreased with increasing contents of layer silicate clay minerals and/or increasing base saturation of the soil. Consequently it was almost absent in the Haplustoll, which contains montmorillonite and kaolinite. The cation effect on P solubility has direct practical implications for oxidic soils because it affects P availability to plants at low P application rates, as was demonstrated by pot experiments with the Eutrustox. Increasing Ca concentrations were significantly related to lower P solubility and as a result lower P uptake and lower yields of Sudangrass. Consequently the Ca : P molar ratio in applied fertilizers has implications for P and also cation availability. It was demonstrated that by manipulating the Ca : P ratio one could increase nutrient (P, K and Mg) uptake and yields of Sudangrass and decrease the leaching losses of cations (Na, K, NH4 , Mg, Ca). As a result the efficiency of applied fertilizers can be improved considerably.
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ItemAdsorption, denitrification, and movement of applied ammonium and nitrate in Hawaiian soils( 1974)The factors influencing adsorption, denitrification. and movement of applied ammonium and nitrate in tropical Hawaiian soils were investigated. Suggestions are incorporated to maximize crop utilization of field-applied fertilizer nitrogen and to minimize loss of mineral nitrogen through leaching and denitrification. Some oxidic tropical soils, such as the Hydrandepts and Gibbsihumox, in Hawaii were found to adsorb nitrate significantly in pH ranges below 6. Non-specific anion adsorption is believed to be the major mechanism by which nitrate was adsorbed. The zero point of change (ZPC), which has a close relation with non-specific anion adsorption, is defined as the pH where the net sum of charges is zero. The high ZPC of the subsoil of the Hydrandepts was attributed to the extensive hydration of their iron and aluminum oxides. Hydrolysis and polymerization of the hydrated oxides were suggested as major mechanisms for the decrease of ZPC and pH on drying the Hydrandepts. Any change in the ZPC was shown to vary the nitrate adsorption. The significant decrease of nitrate adsorption due to dehydration of the Hydrandepts was explained by the change in the ZPC, pH, crystallinity, and surface area on drying. Since this dehydration process is irreversible, it was concluded that these soils should not be allowed to dry excessively by exposure to direct sun and wind so as to preserve their high exchange capacities, both for anions and cations. The surface of the Hydrandepts and Gibbsihumox became less positive or more negative on liming, and this was reflected in the (increased) ammonium and (decreased) nitrate adsorption by the limed soils. The finding that raising of soil pH beyond 5.5 with liming produced N03 repulsion in these soils should be taken into consideration in any liming program. Denitrification loss was found to be important only in soils with large amounts of water-soluble organic matter and nutrients. Available energy source appeared to play a dominant role in denitrification. N2 and N2O gases were the prime denitrification products in all the soils studied. Denitrification potential was very low in Oxisols with poor organic carbon (both water-soluble and total) content. In an infiltration study, it was found that the practically irreversible adsorption of ammonium was responsible for its retention in the Molokai soil. It was further shown that the higher the amount of water infiltrated, the deeper was the position of nitrate peak. An explanation is given on how to take advantage of the lag of nitrate peak with respect to the wetting front in the initially moist soil during transient water flow. For soils with the same initial moisture content, the depth of nitrate peak was in direct proportion to its wetting front. Thus by controlling the wetting front, one can control the depth of maximum solute concentration, irrespective of the rate of water application. In short, modified management practices based on the knowledge of nitrogen transformation and transport in soils as well as nitrogen uptake by crops will ensure efficient (nitrogen) fertilizer use in crop production with a minimum chance for the pollution of ground water by nitrate.
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