Ph.D. - Agronomy and Soil Science

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Effects of Calcium Silicate on Yield and Nutrient Uptake and Mechanism of Silicon Transport in Plants
(University of Hawaii at Manoa, 1971) Thiagalingam, Kandiah
The effect of calcium silicate on yield and nutrient uptake by plants and the mechanism of Si uptake were studied in a series of three experiments. First, response to Si was measured on 22 plant species grown on two soils with four levels of calcium silicate in a greenhouse; second, corn was grown in the field to determine the magnitude of response to residual Si with variable P and pH levels; and third, five plant species were grown in culture solutions at varying transpiration rates to study the mechanism of Si uptake. Response to calcium silicate differed with species and the same species grown on different soils had variable amounts of Si and P depending on the Si contents of the soils. In general the 2.2 T Si/ha application produced maximum yields in both soils and in some species it produced yields comparable to those with 8.8 T Si/ha at lower cost. Silicon concentrations in different plant groups were in the following order: grains > grasses > vegetables and fruits > legumes except for those of the two Desmodiums in which concentrations were similar to those of grasses. Plant Ca concentrations generally increased whereas Mg, Mn, A1 and Fe concentrations generally decreased when calcium silicate was applied. Silicon concentration was greatest in papaya and pineapple leaves and in sugarcane sheaths and was lowest in stems. Hawaiian Cement Corporation (HCC) and Tennessee Valley Authority (TVA) calcium silicates generally produced higher yields than Technical grade (TG) calcium silicate, especially at low rates and in the third and fourth harvests. Plant Si concentrations in both HCC and TG calcium silicate were generally higher than in the TVA material indicating greater Si availability in these two materials. Ear corn yields in the field were significantly increased by P applications but were not significantly affected by residual Si or pH. Highest stover yields were obtained at pH 5.5 suggesting increased Si solubility at this pH may have increased stover yields by increasing mechanical strength and P availability. The application of 280 kg P/ha with Si produced yields nearly equal (98%) to those of 1120 kg P/ha without Si suggesting that comparable yields at lower cost may be obtained with the combination of high Si and low P, than with high P alone. Corn leaf Si values of 0.5 to 0.6% at silking appeared adequate for corn growth. Silicon taken up by the plant is more closely related to soil Si extracted with water than with sulphuric acid. Multiple regression analysis with yield and leaf nutrients indicated that Si, P and Fe are especially important for stover production while P, Ca, K, A1 and Fe are important for ear production. A statistically significant increase in the amount of water transpired per gram of dry weight with decreasing relative humidity was found in all species except D. intortum in solution cultures, but no significant increase in Si transport was obtained with increasing transpiration in any species. This suggests that transport of Si in plants is not related to transpiration. In continuous dark, plants accumulated Si in the roots and only sugarcane translocated large amounts of Si to the tops suggesting that metabolic energy is required for Si transport. Additional evidence of active Si transport was provided by the transpiration stream concentration factor (TSCF) values which were above or below one. Silicon concentrations in xylem exudates of D. Intortum, corn and sugarcane were greater than those of external solutions suggesting Si movement by active transport rather than by mass flow. In tomato and alfalfa Si concentrations were lower in exudates than in external solutions suggesting a selectivity mechanism in the root. These experiments demonstrated that both Si and P transport require metabolic energy.
Evaluation of Phosphorus Fertilizer Materials on Two Benchmark Soils of the Tropics
(University of Hawaii at Manoa, 1983) Harris, David J.
One possible strategy for improving the economic attractiveness of P fertilization on acid P-deficient soils in the tropics was investigated agronomically in two field experiments on sites of the Benchmark Soils Project in the Philippines and Indonesia. The specific strategy is the use of phosphate rock for direct application or partially acidulated or thermally altered phosphate rock in place of acidulated phosphates, e.g., superphosphate. The experiments were conducted on Hydric Dystr'andept soil on a site near Naga City, Camarines Sur, Philippines and on a Typic Paleudult on a site located near Kotabumi, Lampung on the island of Sumatra, Indonesia. The experiments compared crop response (primarily maize) to one highly reactive phosphate rock (North Carolina, NC) and one moderately reactive phosphate rock (Central Florida, CF), which were used because they are well characterized with respect Co reactivity. These two P-sources were used in finely-ground form and also each was used in a different minimally altered form. For the North Carolina rock, a minigranular form was used form, Co determine if the minigranulation process can be used Co overcome the handling and transportation problems of the dusty, finely-ground form without reducing agronomic effectiveness. For the Central Florida rock a minigranular form which was 20% partially acidulated with phosphoric acid was used as the minimally altered form to determine if partial acidualcion of moderately reactive phosphate rocks could adequately improve agronomic effectiveness on acid soils. Comparing the results for the two soils sites in the first crop, a large difference between sources is seem on the Hydric Dystrandept, while no significant differences are seen between sources on the Typic Paleudult. In the second crop, fresh applications of superphosphate were made on former control plots on both sites and the other treatments were left as residuals. On the Hydric Dystrandept significant differences between sources are seen in the residual effects. On the Typic Paleudult, soybeans were planted, and no significant differences are seen between residual effects of the sources. The higher P requirement evidenced by the Hydric Dystrandept as compared to the Typic Paleudult, made reapplication necessary at all rates for the third crop on the Hydric Dystrandept, whereas for the Typic Paleudult, reapplication of all sources was made only on the LO kg/ha plots, on which 70 kg P/ha were applied to permit comparison with the residual 80 kg P/ha treatments. The third season yield results again show no significant differences between sources on the Typic Paleudult, even for the reapplications of 70 kg P/ha, whereas some significant differences are seem for the reapplication on the Hydric Dystrandept. With respect to rock modifications on the Hydric Dystrandept, where differences between sources are detected, minigranulation of the NC rock did not reduce its effectivesness, thus confirming the agronomic viability of the process. Also on the Hydric Dystrandept, partial acidulation did improve the performance of the OF rock, but not sufficiently to make it equal Co superphosphate or the NC forms. In summary, these results indicate that the Typic Paleudult is well suited for direct application of phosphate rocks of moderate and possibly lower reactivity, whereas the Hydric Dystrandept requires phosphate rocks of high reactivity to obtain yields comparable to those of superphosphate. This difference in performance of phoshpate rock between the two soils can be related to the slightly lower pH of the Typic Paleudult and also, its lower P-sorption capacity, in comparison to the Hydric Dystrandept. The results from the post-harvest P soil test analyses indicate that neither the modified Truog nor the Bray P I procedure can be satisfactorily used to predict residual P in the Hydric Dystrandept when P-sources varying in solubility are used. In the Typic Paleudult there is some indication that the Bray I procedure underestimates residual P from the CF sources; however, it appears that minor modification of the procedure by increasing the solution to soil ratio could overcome this problem. This is considered to be a worthwhile area for research since direct application of phosphate rock over the complete range of solubility appears to be an agronomically advisable practice for the Typic Paleudult and similar soils.
Soil Water Hysteresis in the Inter-Aggregate Voids of Two Hawaiian Oxisols
(University of Hawaii at Manoa, 1974) Santo, Lance T.
Soil Nitrogen Mineralization as Affected By Drying, Liming and Sewage Sludge Addition
(University of Hawaii at Manoa, 1980) Ahmad, Nazir
This investigation was undertaken to determine the effect of drying and liming on soil nitrogen mineralization, to measure in N-supplying power of soils and to assess the effect of soil type on mineralization of nitrogen from sewage sludge. Laboratory, greenhouse and field experiments were conducted on a number of soils from the Hawaiian Islands. Air and oven-drying for 12 weeks increased the amount of mineral-N in five soils studied. Oven-drying released about 10-40 times more N than air-drying. Most of the mineral-N was released as NH^-N. Cultivation of undisturbed soil in the field resulted in more N being mineralized than from soil which was left undisturbed. Dry matter yield of corn was also affected when grown on air and oven-dried soils. Air-drying was more beneficial to corn yield in the Kaiwiki (Typic Hydrandepts). However, oven-drying had harmful effects on the growth of corn in this soil. Air-drying had little effect on the growth of corn in the Maile 7 (Hydric Dystrendept) soil. But in the oven-dried soil plants were much more healthy and more dry matter yield of corn was produced, compared to the control. The effect of lime application on N mineralization was studied on the Paaloa (Humoxic Tropohumult) and Wahiawa (Typic Eutrustox) soils in the field. The Paaloa soil had never previously been cultivated or limed. The Wahiawa soil had been limed twice before. Liming at 2 and 4 tons/ ha resulted in greater N mineralization than the control in the Paaloa soil. However, liming from a pH of 4.7 to 7.1 had little effect on the amount of N mineralized in the Wahiawa soil. An evaluation of the N supplying power of seven soils was made. Two chemical extraction methods as well as aerobic incubation procedures at 25°C and 35°C were used to obtain an index of N availability. Nitrogen mineralized was correlated with N-uptake by corn in the greenhouse. Aerobic incubation at 25°C was significantly correlated (r=0.96) with the N-uptake by corn. Incubation at 35°C was also highly correlated (r=0.92). The chemical methods employed were, by comparison, unsuitable in evaluating the N status of these soils. The amount of N mineralized from anaerobically-dried sewage sludge when mixed with two soils was very small, and depended on the soil type and the sludge rate. In the Waimea soil (Typic Eutrandept), 3-4% more N was mineralized than in the Wahiawa soil (Humoxic Tropohumult) when the sludge was applied at 22.4 and 44.8 tons/ha rates. N minrealization potential (Nq ) did not adequately predict the actual N mineralized from the soil: sludge mixtures. A two-function equation with two values of N q may be necessary to adequately describe N mineralization in sludge amended soil, because of two different N mineralization rates. One function describes the release of N from a readily-mineralizeable fraction in early incubation (0-4 weeks), while the other function describes the later r e lease of N from the more stable fraction in sewage sludge.
Calibration and Validation of the IBSNAT/CERES Rice Model
(University of Hawaii at Manoa, 1987) Jang, Li-Ling Lin
Two rice varieties were subjected to two nitrogen rates and three temperature regimes in the greenhouse and growth chambers to study the effects of temperature, variety and N fertilization on N uptake, development and growth of rice. Nitrogen fertilization had a significant effect on grain and straw yields for both varieties. High nitrogen application resulted in high grain yield and N stress reduced biomass production but had no effect on the timing of phonological events of variety Starbonnet, but delayed panicle initiation in variety K-C-A. Temperature affected grain yield and nitrogen uptake during the grain filling stage. High day and night temperature hastened maturation and resulted in lower filled grain percentage, lower 1,000-grain weight and lower overall grain yield. Nitrogen concentration and N uptake were higher in the higher temperature. However, the persistence of green color and a low ratio of grain N to straw N indicate that nitrogen translocation from straw to grain was diminished by the high temperature. The IBSNAT/CERES Rice Model was calibrated and validated with data collected from field experiments under a wide range of agroenvironments. The model was able to adequately predict phenological development for a wide range of agroenvironments. Model prediction of final biomass was also acceptable. The model is sensitive to seasonal variation and altitudinal difference and is able to mimic the high sensitivity of rice to temperature and solar radiation.
Evaluating and Mapping the Fertility of Soils of the Island Of Maui
(University of Hawaii at Manoa, 1983) Duque, Alvaro Jose Parra
Geostatistical approach to the mapping of acid sulfate soils
(University of Hawaii at Manoa, 1985) Ahmad, Faridah Hj
Acid sulfate soils are common along the west coast of West Malaysia. These soils occur in small isolated areas and are difficult to locate. One approach is by analyses of spatial dependence of some soil properties typical of acid sulfate soils determined on samples in those areas. Geostatistics permits analysis of spatial dependence and interpolation of soil properties at unsampled locations. These methods were used to analyze soil properties in the Kuala Selangor area/ West Malaysia which are usually characteristic of acid sulfate soils. Spatial dependence was observed in soil pH/ extractable Al/ soluble SO4 and electrical conductivity. The surface 0-15 cm of oxidized soil/ had approximately equal ranges of spatial dependence of soil pH/ extractable aluminum/ soluble SO^ and electrical conductivity. At the 15-30 cm depth/ extractable Al had a greater range of spatial dependence than did soil pH. Extractable Al is an important characteristic of acid sulfate soils especially when considering soil acidity and liming. Range of spatial dependence of extractable Al is useful in determining the sampling distance. These data suggest that there should be no more than 4 km between samples and preferably much less. The map of individual soil properties was useful in indicating location and extent of acid sulfate areas. The coincidence of isarithms of soil pH/ extractable aluminum/ soluble SO4 and electrical conductivity at 0-15 cm and 15-30 cm depths indicates acid sulfate areas. Sampling frequency was probably inadequate to reveal spatial dependence in nutrient concentrations of oil palm in the Kuala Selangor area. Detrimental effects of acid sulfate soils were evident in lower P concentrations in oil palm fronds. In the wetland rice area/ pH of dry soil was used as an indication of possible acid sulfate soils. Using this criterion/ areas of potential acid sulfate soils were greater than those indicated by the soil survey map although there were large estimation variances. Low density sampling in some areas may account for some of the reasons. Thus spatial dependence analyses by the geostatistical approach is useful in providing base information for the soil survey and also in mapping specific soil constraints. Locations and extent of soil constraints were napped with a known precision.
Predicting change in residual extractable P for site specific management in paddy soils of Indonesia
(University of Hawaii at Manoa, 1996) Pandutama, Martinus H.
Paddy-soils in Java, Indonesia, have been intensively fertilized with nitrogen (N), phosphate (P), and potassium (K) for at least three decades through centralized government subsidy programs, such as BIMAS, INMAS, INSUS, and SUPRAINSUS. One side effect of these programs has been an accumulation of soil phosphorus (P) to excessive levels. The N, P, and K nutrients were added to all fields in rice production without modification for soil P status or for soil properties. The goals of this study were to: 1. ensure sustainable rice production; 2. improve nutrient efficiency; and 3. improve phosphate management in paddy soils to reduce both fertilization cost and environmental hazards. The objective of this study was to develop a mathematical model to predict how long P fertilization could be suspended and how to tailor P fertilization to soil criteria. A mathematical model was developed to predict extractable P as a function of frequently measured soil properties, namely initial extractable P, pH, clay content, organic carbon content, and clay physical activity. The model for HCl-extractable P status in paddy rice soil was: EP, = {0.67 EPi - 11.63} + (22.26 OC) + (0.006 CLAY P) + (59.13 OC EXP(-(-0.14 + 0.32 CAT) Time)} The resulting model was combined with a geographical information system (GIS) software, ARC/INFO, to map P status and to predict the change in extractable P of paddy soils of Java with successive cropping. The model was also used to estimate site specific P recommendations which then mapped and analyzed by GIS. Two scenarios of the P fertilization strategies were considered: 1. A) Fifty kg TSP ha"' would be applied to soils with medium and high extractable P, applied in every 4 crops; B) Fifty kg TSP ha"' for soils low in extractable P, applied in every crop. And, 2. A) Fifty kg TSP ha’^ would be applied to soils high in extractable P, applied once every 8 crops; B) Fifty kg TSP ha'' for soils medium in extractable P, applied once every 4 crops; and C) Fifty kg TSP ha"' for soils low in extractable P, applied to each crop. Approximately 85 000 to 94 000 tonnes of TSP fertilizer per crop would be saved compared to the Centre for Soil and Agroclimate Research (CSAR)/ government recommendations if the first and second scenarios were followed, respectively. The CSAR/government recommendations are: 1. Fifty kg TSP ha-1 applied to soils high in extractable P, once every four crops; 2. Seventy-five kg TSP ha-1 applied to soils medium in extractable P, two times every four crops; and 3. One hundred twenty-five kg TSP ha-1 applied to soils low in extractable P, every crop.
A geographical analysis of change in a Hawaiian sugarcane plantation
(University of Hawaii at Manoa, 1996) Kilham, Phoebe
Efficient use of irrigation water when water supplies are limited is crucial to sugarcane production. This project examines technological change in relation to water management at Hawaiian Commercial and Sugar Company (HC&S) of Puunene, Maui in the context of spatial information management. These include the change from furrow irrigation to drip irrigation, the discontinuation of the evaporation pan network, and managing with a computer water balance model. A field history database of sugarcane harvests at HC&S provided data for a comparison of furrow irrigation and drip irrigation. A combination of statistical and mapping tools were used to evaluate soil, climate, and management variables over space and time for the entire plantation. The topic of greatest concern to HC&S management is "Where to put water when water is short". An objective of this study was to use a simple geographical information system (GIS) system to spatially organize soil and weather data needed for water allocation decisions. SCS Soil Survey 7.5 minute quadrangles Wailuku, Maalaea, Paia, Puu o Kali, and Haiku were combined to form a continuous soil map for HC&S plantation. HC&S field boundaries were overlaid with the soil map and a database of soil types by field was created. Forty-five years of harvest information including yield, irrigation, and climate variables for almost 3,000 harvests were analyzed spatially using maps and over time using both maps and graphs. Multivariate analysis techniques were used to analyze relationships between variables with different spatial groups. Sugarcane yields increased after the plantation converted to drip irrigation. The spatial pattern of yields also changed. With furrow irrigation the highest yields were in the Keahua division which had silty clay loam soils. With drip irrigation, coarser soils in the Maalaea division became the highest yielding. With the discontinuation of the network of evaporation pans in the late 1980s the scale of information collected on water demand was reduced. Water management by computer depends on representative data. Improved weather data will help direct where irrigation water is most needed.
The Properties and Genesis of Soils Derived from Pahala Ash in Kau District, Hawaii
(University of Hawaii at Manoa, 1969) Hassan, Tjetje S.
Evaluation of Soil P and K Extractants for Soils and Crops of Hawaii
(University of Hawaii at Manoa, 1994) Cai, Tingting
Four greenhouse pot experiments were conducted to evaluate the performance of P and K extractants on two Hawaiian soils in terms of their correlations with the performance of two crops that are grown in Hawaii. The extractants assessed were Modified Truog, Mehlich3, Olsen, and Resin for P and NH4OAC, Mehlich3, and Resin for K. The Modified Truog, Olsen, and NH4OAC extractants are commonly used in Hawaii. The Mehlich3 and Resin extractants have not been well tested here yet, but their capacity to extract both P and K simultaneously is a potential advantage over the other methods. The soils were an Ultisol and an Andisol, both of which were amended to establish a wide range of soil P and K concentrations. For both soils, Mehlich3 P and Resin P were as well related with plant response parameters (dry matter yield and P uptake) as were Modified Truog P and Olsen P. Test values from all four methods were very well correlated with one another, with Resin P being slightly less well correlated than other three. In term of the accuracy of diagnoses, the sensitivity of P test values to change of soil P levels, and C.V. for sampling, Mehlich3 usually ranked between Olsen and Modified Troug extraction methods while Resin P performed worst overall. Mehlich3 K performed as well as NH4OAC K in both soils for crop tested in terms of the coefficients of determination for regressions of K uptake and K applied with K extracted, and in terms of the sensitivity of K test values to the change of soil K levels and the C.V. for sampling. In both soils, however, Resin K was as well correlated with NH4OAC K as was Mehlich3 K. However, in terms of the sensitivity of K test values and the C.V. for sampling, Resin K usually did not perform as well as the other methods. These results suggest that it would be practical to switch from the conventional procedures, with separate extractions for P and K, to a simultaneous P and K extraction with Mehlich3 for these soil-crop combinations. Use of a simple linear regression model would allow conversion between results obtained from a Mehlich3 P and K extraction and those obtained from Modified Truog P, Olsen P, and NH4OAC K extractions.
Management-Oriented Modeling: Optimizing Nitrogen Management using Computerized Artificial Intelligence
(University of Hawaii at Manoa, 1997) Li, Mengbo
Increasing nitrate levels in groundwater have caused growing public health concern in recent years. This has prompted research on precision nitrogen management to understand and control nitrogen impact on the environment. Many nitrogen (N) models have been developed to describe the N status and behavior in soil-plant systems, but they are uniformly weak in finding optimal management strategies. To model nitrogen management, Management-Oriented Modeling (MOM), a dynamic simulation model using artificial intelligence (AI) optimization techniques, was developed in this study. MOM was designed as a tool to find optimal solutions for N management to minimize nitrate leaching and maximize production and profits. MOM consists of a generator, a simulator, and an evaluator. In searching for optimal management strategies, the generator produces a group of nodes (management choices). The evaluator uses the built-in knowledge and communication with users to analyze the outputs of the simulator and to guide the generator’s work. A mixed search method that combines hill-climbing method for a global, strategic search with best-first method for a local, tactical search was developed to find the shortest path from start nodes to goals. In this manner, MOM searches for user-weighted goals by simulating the N cycle and management effects on the fate of N in a soil-plant system. In addition to general simulation and evaluation of N fertilization, MOM provides real time decision-aid for within-season management. MOM-guided within-season management uses weather forecasting to estimate rainfall in the near future and simulates the consequences in soil-plant systems. It gives users daily “snapshots” of the N status in soil-plant systems without within-season sampling and testing. Scenarios show that MOM can provide precision nitrogen management that maximizes profits and yields while minimizing nitrate leaching by updating management of irrigation and fertilization within-season. MOM-guided within-season management is a precision tool with high efficiency, low cost and “transparency” for nitrogen management. MOM simulator was evaluated with 11 datasets from Hawaii and Brazil. Calibration and validation results suggest that the model prediction accuracy was acceptable for the field N management.
Genesis of A Climosequence of Soils in The Kohala Region
(University of Hawaii at Manoa, 1967) Gardiner, Harold C.
Evaluating mycorrhizal inoculum levels in soil and quantifying their contribution to the phosphorus nutrition of cowpea
(University of Hawaii at Manoa, 1980) Dowdle, Stephen F.
Influence of vesicular-arbuscular mycorrhiza on Leucaena leucocephala growth, water relations and nutrient acquisition
(University of Hawaii at Manoa, 1987) Ruey-Shyang, Huang
Knowledge of the dynamics of VA mycorrhizal plant systems is fundamental to the understanding of the relationships between VA mycorrhiza, plants and soil. Pot experiments were conducted to: 1) determine early physiological responses to VA mycorrhizal inoculation, 2) measure the acquisition and utilization of water and nutrients, dry matter production and assimilate partitioning in mycorrhizal and non-mycorrhizal plants, and 3) develop a model of VA mycorrhizal influence and its consequences to the physiology and ecology of VA mycorrhizal plants. Leucaena leucocephala seedlings, with and without the VA mycorrhizal fungus (Glomus aggregatum), were grown in a Wahiawa soil (Tropeptic Eutrustox) with soil P levels ranging from 0.005 to 0.429 mg L-1 of P in 0.01 M CaCl2 extract. Without mycorrhizal infection, leucaena plant growth was stunted under low soil P conditions. Even with high P fertilization, the growth of non-mycorrhizal plants was less than the growth of mycorrhizal plants. Daily pinnule sampling, pot weighing methods and multiple 5-day-interval harvests revealed a series of changes in nutrient uptake, dry matter production and water transpiration between mycorrhizal and non-mycorrhizal plants. The series of changes was as follows: 1) Five days after inoculation, plant roots had about 7% mycorrhizal infection. 2) At 10 days, root P concentrations were higher in mycorrhizal plants than in non-mycorrhizal plants. By 15 days after inoculation, increases in shoot P, K and S concentrations were observed in mycorrhizal plants. Shoot Mg and Ca concentrations in mycorrhizal plants were greater than in non-mycorrhizal plants at 20 and 25 days after inoculation, respectively. From 10 to 15 days after inoculation, the flux of P into mycorrhizal roots was greater than that into non-mycorrhizal roots. 3) Elevated nutrient contents in shoots of mycorrhizal plants was followed by superior growth rates. Mycorrhizal plants also allocated more assimilate to leaf growth than did non-mycorrhizal plants. Increased leaf growth was followed by increased transpiration. 4) Leaf area expansion rates and net assimilation rates were greater for mycorrhizal plants than for non-mycorrhizal plants. Greater dry weight was observed in mycorrhizal plants, supporting further growth of the mycorrhizal roots (positive feedback), and 5) Greatest soil volume was explored by the mycorrhizal roots. A scheme to explain these changes is pressed and used to describe processes involved in the soil-mycorrhiza-plant system. In contrast, the flux of P into non-mycorrhizal roots decreased during the period 10 to 15 days after transplanting. The resulting low P content in non-mycorrhizal plants further reduced relative leaf expansion rates, net assimilation rates and later reduced relative root expansion rates (negative feedback). Nevertheless, when non-mycorrhizal plants were subsequently inoculated they eventually attained a similar size and weight as mycorrhizal plants. The stunting of non-mycorrhizal plants thus appears to be reversible and probably is part of a survival strategy which reduces energy use while retaining the potential for mycorrhizal infection.
The Effect of Phosphorus, Potassium and Calcium Fertilization on Peanut Yield, Quality and Nutrient Uptake
(University of Hawaii at Manoa, 1963) Eastman, Clyde
Alley Cropping and Green Manuring For Upland Crop Production in West Sumatra
(University of Hawaii at Manoa, 1989) Evensen, Carl Lovell Imaikalani
Green manuring and alley cropping were studied as means of improving crop production and reducing lime requirements in Sitiung, West Sumatra. Two experiments were conducted between 1985 and 1988 on acid, high aluminum soil (pH of 4.2 to 4.7 and Al+H saturation of 70 to 90 %). Low levels of external inputs were used in these experiments. In the alley cropping experiment, three tree species Paraserianthes falcataria. Calliandra calothvrsus, and Gliricidia sepium and a no tree control were compared as well as three lime rates of zero, 750 kg ha-1, and liming to 25% Al+H saturation. Paraserianthes and Calliandra both grew vigorously (producing about 3 T leaf ha-1 year-1) and showed no consistent response to lime, even at Al+H saturations of greater than 70%. Gliricidia grew poorly (producing about 0.5 T leaf ha-1 year-1) with growth especially limited at high soil Al+H saturation. Upland rice (Orvza satival and cowpea (Viona unquiculatal crops responded to both lime and green leaf manure (GLM) application. Paraserianthes GLM application doubled rice yields and quadrupled cowpea yields as compared to control plots. However, overall yields declined over the study period, possibly due to increasingly sporadic rainfall distribution. Also, Paraserianthes hedges began to die after four years while Calliandra hedges remained vigorous. Ongoing studies are needed to evaluate sustainability. Economic analyses procedures were developed for comparing alley cropping and liming practices. The Paraserianthes + Low lime rate treatment was shown to be most profitable. If lime is not available, alley cropping with Paraserianthes may be more profitable than farmer’s current practices. In the second experiment, Crotalaria usaramoensis. Calopogonium mucunoides and Centrosema pubescens were grown as green manure crops during two dry seasons and were applied to a rotation of upland rice or maize followed by peanuts. Upland rice did not respond to either liming or green manure application, probably because it is tolerant of high soil acidity. Subsequent maize (Zea mays) and peanut (Arachis hvpoqaea) growth increased with liming, but overall there was little yield increase due to green manure application and little or no increase with inorganic N application. Therefore, the value of herbaceous green manures is questionable in farming systems in Sitiung, while alley cropping may have potential for improving crop yields on limited resource farms.
Nutrient Cycling In Tropical Grasses Irrigated With Dairy Effluent in a Tropical Island Environment
(University of Hawaii at Manoa, 2007) Valencia-Gica, Rowena B.
In Hawaii and other island environments, dairy producers accumulate large quantities of effluent in lagoons. These lagoons can potentially overflow causing the nutrients and other contaminants to pollute the land and associated water bodies. Alternative uses of effluent are urgently needed for a sustainable and environment-friendly dairy production. This study assessed the effects of effluent irrigation on plant and soil (Cumulic Haplustoll) properties. Five tropical grasses—bana {Pennisetum purpureum S.), California (Brachiaria mutica S.), signal (Brachiaria decumbens S.), star (Cynodon nlemfuensis V.) , and suerte (Paspalum atratum S.)—received subsurface drip irrigation of dairy effluent at two rates based upon the potential evapotranspiration (ETp) at the site (Waianae, Hawaii)—2.0 ETp (7 to 44 mm d"‘) and 0.5 ETp (2 to 11 mm d"*). No excessive increases in extractable soil P (81 to 176 mg kg'') and soil solution total P (3 to 9 mg L'') was observed after two years of effluent irrigation. Soil pH and soil solution pH fluctuated over time due to the high soil buffering capacity. Salinity and sodicity were not observed in this effluent-irrigated soil. Soil electrical conductivity (ECspc) declined from 18.0 dS m'' in July 2003 to 2.7 dS m * in Aug 2006—lower than the U.S. Salinity Laboratory’s critical level for classifying soils as saline (4.0 dS m''). Soil exchangeable sodium percentage (6.4 to 10.2%) remained below 15%—critical value critical value for classifying soils as sodic. Brachiaria mutica and P. purpureum yielded the highest dry matter of 57 and 53 Mg ha'' y ', respectively. Average nutrient removal of grasses was 30 to 187%, 13 to 86% and 2 to 14% of applied effluent N, P and K, respectively. Forage quality was within acceptable levels for feeding to dairy cattle. Modeling results showed that total applied phosphorus determines how many animals may be raised and how much area may be utilized to produce the forage. Results indicated that irrigating high yielding tropical grasses with effluent at 2.0 ETp was acceptable for recycling of nutrients from the effluent. Additional monitoring is needed to determine the longer-term impacts of effluent application on soil and plant properties.
Toward Modeling Erosion on Unpaved Roads In Mountainous Northern Thailand
(University of Hawaii at Manoa, 2000) Ziegler, Alan D.
Contributions of road networks and unstable agricultural activities to downstream sedimentation, water shortages, and flooding in mainland SE Asia are not easily determined because scientific understanding of runoff and erosion processes operating on roads is limited. This dissertation work, conducted within the Pang Khum Experimental Watershed (PKEW) in northern Thailand, supports that owing to low saturated hydraulic conductivity (Ks < 1 6 mm h-1), Horton overland flow (HOF) generation occurs more frequently on unpaved PBCEW roads than on other watershed surfaces having higher infiltrability (e.g., mean Ks for agricultural surfaces ranges from 130 to 320 mm h-1)- Because of frequent HOF generation, the road system contributes to stream sedimentation throughout the rainy season. The highly compacted (bulk density = 1.45 Mg m-3) PKEW road surface typically underlies a layer of loose material of finite depth. Instantaneous sediment transport (St) on roads varies because the supply of easily transported surface sediment is constantly altered by overland flow events, traffic, road maintenance, and mass wasting events, both during and between storms. As surface material is removed during an overland flow event, normalized S( declines from an initial peak rate of ~ 3 g J-1 to a steady rate of =0.5 g J-1 The mechanical stress associated with vehicle passes during a storm increases the availability of loose material, producing 2-4 fold increases in St, and sediment concentration (Ct) values. Herein, rainfall simulation data, surveys of traffic phenomena, and soil property measurements were used to parameterize the physics-based KINER0S2 model for simulating road runoff and erosion. During model validation, instantaneous discharge was simulated well (root mean squared error (RMSE) = 14%). However, because KINEROS2 equations do not “describe” road erosion processes accurately, St was simulated poorly (RMSE = 51.6%). To improve modeling, a methodology recognizing the dynamic erodibility (DE) of a road surface was introduced. By explicitly simulating removal of a layer of loose material, the DE modeling technique improved prediction of St (RMSE decreased to 35.4 %). Finally, a systematic approach is presented to implement DE modeling on any road surface where baseline erodibility and sediment availability can be quantified.
Computer Simulation of Pineapple Growth, Development and Yield
(University of Hawaii at Manoa, 1992) Zhang, Jingbo
Fruit yield and harvest date of pineapple {Amnas comosus (L.) Merr.] are difficult to predict. Site-specific studies improve the predictability at one location but usually cannot be generalized to other environments. This study examined the effects of plant population density (PPD) and planting date (PD) on pineapple growth and fruiting and the data were used to develop a pineapple growth simulation model. ‘Smooth Cayenne’ pineapple was planted at Kunia, Hawaii; the crop was drip-irrigated. PPDs ranged from 2.61 to 12.81 plants m-2 and PDs were June and August 15, and October 18, 1989. Flower development was forced with ethylene on September 18, 1990. Leaf emergence rate was constant until 200 days after planting (DAP) and then decreased 0.9 leaves 1000-°C-day-1 with each increase in PPD of one plant m-2. Dry weight per plant decreased as PPD increased and as PD was delayed. Light interception reached 95% at a leaf area index of 4 to 5, which was attained at 350 DAP at 12.81 plants m-2 and later as PPD decreased. Dry matter partitioning (DMP) to leaves and stem during vegetative growth was not affected by PPD or PD. DMP to stem during fruiting decreased linearly and DMP to fruit increased curvilinearly as PPD increased and as PD was delayed. Fruit harvest date was delayed seven days for each PPD increase of 2.5 plants m-2 from 2.61 to 12.81 plants m-2. Fruit yield was asymptotically related to PPD; the economic yield-PPD relationship was parabolic. There was no effect of PD on rate of leaf emergence or fruit development. A pineapple simulation model (ALOHA-Pineapple) was developed using data from the experiment and the literature. ALOHA-Pineapple is process-oriented and incremented daily. It simulates the effects of PPD, PD, plant size at planting and forcing, and weather on crop growth and yield. When ALOHA-Pineapple was validated with data from eleven plantings in four locations in Hawaii, pineapple growth, fruit development and yield was simulated with reasonable accuracy although harvest date and yield were over- and under-predicted in some locations. ALOHA-Pineapple has potential to serve as a frame-work for pineapple research and as a decision aid for farmers.

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