Full Canopy Closure Research Articles

Comparison of growth and yield of kiwifruit on different vine support structures

Abstract Vine growth, pruning requirements, yield, and postharvest storage of kiwifruit (Actinidia deliciosa) grown on five different vine support structures were compared over 5 years from grafting. Support structures were winged T‐bars and pergolas (standard structures), Lincoln T‐bars, divided T‐bars, and A‐frames. Cumulative length of fruiting canes in the 3 years to full canopy closure was greatest for Lincoln T‐bars, A‐frames, and pergolas, and least for winged and divided T‐bars. The proportion of budbreak was higher on pergolas than on the three T‐bar systems and was least on A‐frames. Floral budbreak and flowers per floral shoot were also lower on A‐frames than on the other systems. Cumulative yields of export fruit were highest for pergolas and winged T‐bars, and lowest for A‐frames. Differences in postharvest storage were detected between fruit from different structures, but these differences were not consistent among years. The time required to prune each vine was least for pergolas and winged...

The structure of four home gardens in the Pet�n, Guatemala

Forest-covered home gardens around the tropical world vary in their structure, but serve to supply food and other products for direct family consumption or marketing. Little quantitative data exist defining home garden structure. Thus, this study was undertaken to examine the variation in home garden structures in response to market or household needs and the subsequent variation in light interception and productivity. Four home gardens were studied in the Department of the Peten, in northern Guatemala. Areal extent and height of canopies were mapped in transects through four gardens representing a range of site water regimes and market orientation. Light intensities incident on the ground were measured along each transect to assess light use. Results showed structural complexity, with full canopy closure in the one or more layers within the canopy for most gardens. The garden architectures made efficient use of light and space, with intersive management for food and fuel production. Farmers grew the crops for both cash and family subsistence. One home garden on a comparatively dry site with shallow soil seemed less structured, with only a single broken canopy layer, but with diverse species of plants. The results indicate that development of gardens in this area utilized existing trees, thinning them to leave the most useful, and inserting other desirable trees and shrubs in the understory and in open spaces. This strategy seemed to maximize light use, regardless of market orientation. This look at the structure and composition of four home gardens, in a forested area of current immigration, demonstrated (1) variety of organization and plant components, (2) different architecture for different soil/site conditions and market orientations, and (3) efficient use of available light through the arrangement of plants.

GAS EXCHANGE RATES BY A STAND OF SOYBEANS GROWN IN A TIGHTLY SEALED CHAMBER

Soybean plants [Glycine max (L.) Merr. cv. McCall] were grown from seed to harvest (90 days) in NASA's Biomass Production Chamber. The chamber provides approximately 20 m2 of growing area with an atmospheric volume of 113 m3. Photosynthesis and respiration rates of the stand were tracked by monitoring CO2 increase during the 12-h dark period and the subsequent drawdown to controlled set point (1000 ppm) when the lamps were turned on each day. Stand photosynthesis [under 875 μmol m-2 s-1 photosynthetic photon flux (PPF)] peaked at 35 μmol m-2 s-1 at 30 to 35 days after planting (DAP) and averaged 22 μmol m-2 s-1 throughout the life cycle. Dark period respiration peaked near 8 μmol m-2 s-1 at 30 to 35 DAP and averaged nearly 5 μmol m-2 s-1 throughout the life cycle. Prior to full canopy closure near 30 DAP, the light compensation point (LCP) for stand photosynthesis was lass than 100 μmol m-2 s-1 PPF; by 54 DAP the LCP had increasad to 175 μmol m-2 s-1. Stand transpiration rates peaked at 8.2 L m-2 day-1 at 40 to 45 DAP and averaged 4.3 L m-2 day-1 throughout growth.

Genotypic Variation in Carbon Isotope Discrimination and Transpiration Efficiency in Wheat. Leaf Gas Exchange and Whole Plant Studies

The relationship between carbon isotope discrimination, Δ, measured in plant dry matter and the ratio of intercellular to atmospheric partial pressures of CO2, pi/pa, in leaves was examined in two glasshouse experiments using 14 wheat genotypes selected on the basis of variation in Δ of dry matter. Genotypic variation in Δ was similar in both experiments, with an average range of 1.8 x 10-3. Variation in pi/pa was significant but the range in pi/pa was relatively small, averaging 0.075. In both experiments, Δ measured in dry matter and pi/pa measured in flag leaves were positively correlated. Variation among genotypes in pi/pa was attributed, approximately equally, to variation in leaf conductance and in photosynthetic capacity. The relationship between plant transpiration efficiency, W* (the amount of above-ground dry matter produced per unit water transpired) and � was also examined. There was a negative correlation between W * and Δ; under well watered conditions and under gradually increasing terminal water stress. The relationship between W* of stressed plants and Δ measured in well watered plants was also negative. These results indicate that genotypic variation in Δ measured in dry matter should provide a reasonable measure of genotypic variation in long-term mean leaf pi/pa in wheat. Further, selection for improved plant transpiration efficiency in wheat under both well watered and terminally water- stressed conditions should be possible based on Δ measured in well watered plants. The extent to which such selection will be effective in improving transpiration efficiency at the field canopy level may depend on the influence of boundary layer resistance on transpirationsal water loss. Under well watered conditions and at full canopy closure, the influence of boundary layer resistance on canopy water loss may be relatively large and stomatal control of water loss may be limited. Under water stress, stomatal control of canopy water loss will be greater.

Microprocessor-Based Data Acquisition and Control Software for Plant Growth Chambers (Spar System)

ABSTRACT COMPUTER software has been developed for a microprocessor-based data acquisition and control system to measure 64 transducers and to maintain closed loop environmental control for three sunlit Soil-Plant-Atmosphere Research (SPAR) units at Florence, SC. An assembly language program and a BASIC program were written to run concurrently by using a real-time inter-rupt. The assembly language program performs the data acquisition, real-time control, and time keeping. The BASIC program performs the dynamic signal condition-ing, the computation of control parameters, and the con-version and output of the acquired data in engineering units. Environmental control algorithms were im-plemented in software to control temperature, C02 con-centration, and relative humidity. The BASIC program utilizes the history of the absolute deviation from the control levels to compute the control parameters for the assembly language program to implement. The temperature control algorithm enabled control within 0.5 C for control temperatures ranging from 15 C to 35 C with ambient temperatures ranging from 4 C to 32 C. A proportional control algorithm written in BASIC enabled C02 control for three SPAR units within 10 mg/L under changing radiation load with full canopy closure using one infrared gas analyzer. A C02 control algorithm using light response curves is derived to pro-ject C02 uptake and absolute deviations from the control level to correct the coefficients of light response curves. Dynamic environmental control of the SPAR units, which involves process feedback influenced by random climatic variations, can be obtained using an inexpensive microprocessor-based system. This enables researchers to conduct precise experiments involving climatic variables to provide the necessary inputs for crop simula-tion modeling.