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Understanding the changes in early growth efficiency (GE, growth/leaf area) may improve forest production through the selection of appropriate genotypes at early stages. We investigated different early growth responses of genotypes of Eucalyptus globulus (7), E. nitens (3), and E. nitens × E globulus (E. gloni) (7) in south-central Chile. To evaluate seasonal growth, plants of each genotype were established in a completely randomized block design in coarse sandy soil (i.e., low water holding capacity), with spring and summer irrigation. The current monthly increment (CMI) in wood volume (cm3 tree−1 month−1), and leaf area index (LAI, m2 m−2) were used to calculate GE at 4.1, 7.5, 10.4, 13.4, and 15.4 months of age, corresponding to five growing seasons (first summer, fall, winter, spring, and second summer). The interaction between genotype and season had a significant effect (p

Calibration of sap flux density equations for Eucalytus is required when using sapflow thermal dissipation probes to avoid large underestimations of transpiration and water use. Eucalyptus plantations are expanding in response to global wood demand but are raising concerns about their impacts on water supplies. Sustainable plantation management in areas with water conflicts will require accurate assessments of tree and stand water use. Thermal dissipation probes have been used to estimate tree water use, but recent work suggests that species-specific calibrations may be required to obtain accurate results. In this study, we quantified sap flux density (SFD) in 2-year-old Eucalyptus globulus Labill (Eg) and E. nitens × globulus (Eng) species using the thermal dissipation method developed by Granier. For each species we compared the original Granier equation with species-specific calibrations using whole tree potometers over a 36-h period. Our results showed that on average, Granier’s original equation significantly underestimated SFD in both species, and when scaled to the stand level, tree transpiration (Ec) was significantly lower compared to onsite calibrations. The Granier method also underestimated nocturnal transpiration for both genotypes. Measured calibration coefficients were similar and not statistically different between Eg and Eng. These results highlight the importance of species-specific calibrations using thermal dissipation probes for Eucalyptus species to improve stand water use estimates and inferences about ecological impacts.

The impact of potential future climate change scenarios on the irrigation water requirements (IRRs) of two major agricultural crops (coffee and seed corn) in Hawai'i was studied using the Irrigation Management System (IManSys) model. In addition to IRRs calculations, IManSys calculates runoff, deep percolation, canopy interception, and effective rainfall based on plant growth parameters, site specific soil hydrological properties, irrigation system efficiency, and long-term daily weather data. Irrigation water requirements of two crops were simulated using historical climate data and different levels of atmospheric CO2 (330, 550, 710 and 970 ppm), temperature (+1.1 and +6.4 °C) and precipitation (±5, ±10 and ±20%) chosen based on the Intergovernmental Panel on Climate Change (IPCC) AR4 projections under reference, B1, A1B1 and A1F1 emission scenarios. IRRs decreased as CO2 emission increased. The average percentage decrease in IRRs for seed corn is higher than that of coffee. However, runoff, rain canopy interception, and deep percolation below the root zone increased as precipitation increased. Canopy interception and drainage increased with increased CO2 emission. Evapotranspiration responded positively to air temperature rise, and as a result, IRRs increased as well. Further studies using crop models will predict crop yield responses to these different irrigation scenarios.

Soil moisture and organic matter level affects soil respiration and microbial activities, which in turn impact greenhouse gas (GHG) emissions. This study was conducted to evaluate the effect of irrigation levels (75% [deficit], 100% [full], and 125% [excess] of reference crop evapotranspiration requirements), and organic amendments (OA) type (chicken manure [CM] and bone meal [BM]) and OA application rates (0,168, 336 and 672 kg total N ha−1) on (i) soil physical properties (bulk density, organic matter content and soil moisture content) and (ii) soil carbon dioxide (CO2) emissions from a highly weathered tropical Hawai'ian soil. Carbon dioxide readings were consistently taken once or twice a week for the duration of the cropping season. A drip irrigation system was used to apply the appropriate amount of irrigation water to the treatment plots. Treatments were randomly selected and corresponding organic amendments were manually incorporated into the soil. Plots were cultivated with sweet corn (Ze...

This study determined carbon dioxide (CO2) emissions from a tropical soil amended with organic compost (CP), chicken manure (CM), and untreated controls during three growing seasons of sweet corn (Zea mays L.). The organic amendments resulted in significantly greater CO2 emissions compared with control treatments. The time duration after organic amendment applications significantly affected CO2 emissions, especially during the warmer growing seasons. The cumulative soil CO2 emissions increased in the order of control < CP < CM probably due to a greater microbial activity and to the greater above and below ground biomass production from N fertilization of organic amendments.

Efficient water resource management is one of the most important policy issues facing agriculture in Hawaii in the years ahead. Soil water sensors, multisensor capacitance probes (MCP), have been successfully used for different water management projects. These MCPs monitor water content at multiple depths and at various locations in real-time. The objectives of this study were to determine the effect of water content on field soil bulk density of Wahiawa silty clay tropical soil; measure field saturated hydraulic conductivity of this tropical soil; calibrate MCP system for this soil; and monitor and evaluate real-time soil water content variations under a tomato crop using the calibrated MCP system. Sensor calibration was conducted under laboratory conditions. Soil bulk density at different water contents and saturated hydraulic conductivity were measured on the field. Bulk density increased with increasing water content; there was a 30 percent bulk density increase as a result of 0.25 cm 3 cm -3 water content variation. Compared with the manufacturer's calibration, site specific laboratory calibration of MCP gave a more accurate determination of soil water. Field determined saturated hydraulic conductivity was higher than laboratory determined values reported in the literature for the same soil type. Real-time soil water content monitoring within the root zone showed substantial variations due to water input (irrigation and rainfall) and water output (evapotranspiration and deep percolations). However, water content variations were much further reduced in the soil layer below the root zone.

Regulatory agencies are concerned about the high levels of P fertilizers used in some agricultural areas because of potential runoff to aquatic habitats. Farmers in Hawaii traditionally make blanket P applications even in soils high in P. Many farmers, especially those growing leafy crops, claim to observe responses to P, especially during the cooler winter months. A series of 15 field experiments were conducted over a 2-year period to evaluate the response of three mustard cabbage varieties to five P fertilizer rates across three locations in the state, and across several planting seasons. All experiments were conducted in soils with P levels that the University of Hawaii determined to be high in P. The experimental design for each experiment consisted of three commercial mustard cabbage varieties, and five P application rates (from 0 to 400 kg·ha-1 of TSP). Each plot consisted of a 3-m double-row, with plants spaced 15 cm within the row, and 30 cm between rows, with four replications per treatment. Each experiment thus consisted of 60 plots (three varietie × five P rate × four replications). After the initial P applications were made on each site, three consecutive crops were planted on the same site without making any additional P applications. Data collected included soil fertility prior to initiation and after experiment completion, tissue nutrient levels, plant height during crop establishment, and individual head weight of 20 plants per treatment. Our data show that even in soils with initial high levels of P, mustard cabbage responded to P applications, especially at high elevations and during the cooler months of the year. From this data we recommend that the University recalibrate its P fertilizer recommendations for leafy vegetable production in Hawaii.

As many farmers transition toward organic farming, research-based information is required to determine the appropriate rates and timing for the application of available organic fertilizers. Four experiments were conducted over a 3-year period in Oahu, Hawaii, to evaluate the effect of five different organic amendments on the growth and yield of edible ginger. Fertilizer amendments, applied at a rate of 30–60 t·ha-1, included bone meal, a locally available commercial chicken manure-based compost, a commercial Bokashi compost, aged chicken manure, synthetic fertilizer (farmer's practice at 300 kg·ha-1 N), and a control. Each treatment plot consisted of a 10-m row with 15 plants per plot, and five replications per treatment. Ginger was planted in April of every year, and harvested from February to March of the following year. Data collected included soil fertility before initiation and after experiment completion, tissue nutrient levels, plant stands, plant height, and stem number, individual tops and root weight of 5–10 plants per treatment, as well as nematode counts before and after experiment completion. The data showed that similar or greater root weight yields and quality were obtained with the use of organic amendments compared to the use of synthetic fertilizer. Increased yields were obtained when organic amendment and fertilizer applications were split over the growing season. Data will be presented with regard to initial plant stands, tissue levels, and yield trends in response to the several amendments used in these experiments, and management considerations for farmers will be discussed.

To help develop fertilizer recommendations for organic vegetable production in Hawaii, the effects of organic amendments on basil yield were studied in two experiments. The treatments were synthetic nitrogen applied at 100 kg·ha–1 per crop, organic amendments applied at a rate of 8–160 MT·ha–1, and an unammended control. Each treatment was replicated four times in a RCB design. In the first experiment, chicken manure was the organic amendment at 8 MT·ha–1 with a single basil variety grown. In the second experiment, conducted at the same location immediately following the first experiment, the organic amendment was locally produced compost (0.3% N) applied at 40 and 160 MT·ha–1 with three basil varieties grown. Data taken included soil fertility levels before and after experimental completion, marketable yields recorded weekly over 5–10 weeks, and tissue N and nitrate sap analysis measured at two to three different plant growth stages. In the first experiment, treatments receiving chicken manure or synthetic N showed similar yields (256–289 g/plant), which were significantly greater than the control (197 g/plant). Tissue N levels were greatest in the synthetic fertilizer treatment (4.9%) and lowest in the control (4.5%). In the second experiment, there was a differential response by varieties to treatments with respect to yields. Yields from the compost treatments (292–700 g/plant) were equal to or greater than those receiving synthetic fertilizer (320–651 g/plant) and were generally greater than the control (324–532 g/plant). Tissue N levels were greatest in plants receiving synthetic fertilizer (4.6% to 4.7%) and lowest in the control (4.3% to 4.4%). A positive correlation was found between lab tissue N levels and nitrate sap analysis determination.

In the tropics, weed control is a year-round concern. The use of cover crops in a conservation tillage system allows for the production of a crop biomass that can be killed and mowed, and later used as mulching material to help reduce weed growth. This study compared yields of three vegetable species grown in two conventional tillage systems, one weeded and one unweeded control, and in two no-tillage treatments using two different cover crop species, oats (Avena sativa L. `Cauyse') and rye grain (Secale cereale L.). The cover crops were seeded (112 kg/ha) in Spring 1998 in 4 × 23-m plots in a RCB design with six replications per treatment, and mowed down at the flowering stage before transplanting the seedlings. Data collection throughout the experimental period included quadrant weed counts, biomass levels, and crop marketable yields. Weed suppression was compared with the yields of the vegetable crops. The greatest vegetable yields were in the conventionally hand-weeded control and the worst in the un-weeded controls. Weed species composition varied depending on the cover crop species treatment. The rye better suppressed weed growth than the oats, with greater control of grass species. Rye, however, suppressed romaine and bell pepper yields more than the oat treatments. Similarly greater eggplant yields and more fruit per plant were found in the oat treatment than in the rye. Both cover crops suppressed weed growth for the first month; however, by the second month most plots had extensive weed growth. This study showed that at the given cover crop seeding rate, the mulch produced was not enough to reduce weed growth and provide acceptable yields of various vegetable crops.

Portable chlorophyll fluorometers have made it possible to evaluate the photosynthetic efficiency of photosystem 11 for vegetable crops under ambient conditions. A sampling protocol was first established to eliminate variability due to positioning of the fiber optics in relation to the leaf, leaf selection, and natural environmental variability. Fluorescence parameters of the quantum yield of noncyclic electron transport (DF/Fm') and electron transport rate (ETR) were taken from several economically important vegetables under ambient conditions between 11 and 14 h. The objective of the second part of the study was to conduct in situ chlorophyll fluorescence and biomass determinations as affected by salt stress and N deficiency. DF/Fm' and ETR were studied in rhizobium inoculated, noninoculated and inorganic N-fed soybean and differences in fluorescence were related to yield. The influence that salt stress, and several N rates have on fluorescence photochemical quenching (qP) and nonphotochemical quenching (qN), NPQ ([Fm-Fm']/Fm'), DF/Fm' and ETR for hydroponically grown lettuce will also be presented.

Methanol sprays reportedly increased yields of several crops in Arizona by 50 to 100 percent (Nonomura and Benson PNAS 89:9794(1992). Reports from other parts of the country have shown conflicting results with regards to the effect of methanol sprays on yields of horticultural crops. Several greenhouse and growth chamber (controlled temperature. day length, and photosynthetic photon flux) experiments were conducted to evaluate the effect of methanol sprays on the growth and productivity of several vegetable crops in Hawaii. Treatment spray solutions consisted of 20-25% methanol, 0.5% low biuret urea. 0.001% chelated iron, and 0.02% surfactant. Control sprays only contained urea, chelated iron, and surfactant. Each experiment consisted of at least 5 weekly methanol sprays. Flowering cabbage, Brassica campestris var. parachinensis, had greater biomass production when sprayed with methanol in the late summer months. Similar results were obtained with choi sum in a 2 by 2 factorial experiment with methanol and water stress treatments. However, choi sum did not respond to methanol treatments in follow-up greenhouse trials. perhaps attributable to the shorter and Overcast days experienced in the fall and winter. Okra, chili pepper, and eggplant showed no response to methanol sprays. Okra showed a trend toward increase yields in response to methanol sprays, but differences were not significant. Follow-up studies in the greenhouse and in the field, which include evaluation of photosynthetic efficiency through chlorophyll fluorescence determinations will be presented.