The efficiency of dry matter production by plants can be defined as the ratio of energy output to energy input. Energy input depends on the spectral quality of solar radiation that is intercepted by plant tissue, which depends on leaf area and orientation as well as canopy architecture. Energy output depends on the efficiency with which intercepted radiant energy is used in photosynthesis, which is influenced by temperature, water availability, pest pressure, nutrient supply, and canopy density. The amount and quality of light that intercepts a canopy differs according to seasonal and daily cycles. The tilt of the Earth’s axis causes seasonal changes in the absorption of solar radiation. On a typical summer day in the northern hemisphere, the earth rotates in such a way that the sun appears to move across our sky from the northeast to the northwest. Although the movement we see is caused primarily by the earth’s rotation, row crops can be positioned to take advantage of this sun/earth interaction. Because solar radiation is an abundant and free production input, manipulating potato row orientation for improved light capture and plant growth is a promising strategy for improving crop productivity.
Yield increases within the northern hemisphere from rows oriented along a north-south axis compared to an east-west orientation have been reported in oats, wheat and barley in Illinois; soybeans in South Carolina; bush beans in Kentucky; corn in India, Pakistan Nebraska, and Illinois. However, higher yields in east-west-oriented rows have also been reported for a summer crop of corn in Henan, China. Row orientation had no consistent effect on yields of corn in South Carolina; sunflowers in Minnesota; sorghum in Texas; or cotton in Mississippi.
Precise calculation of the amount of light absorbed by a canopy is complex. However, useful approximations can be arrived at with conceptual models if the assumptions of such models are realistic. When modeling light absorption by row crops, it is convenient to represent a canopy as a hedge separated by paths between the rows. If the amount of radiation absorbed by the canopy of a homogeneous hedge, and the radiation absorbed by the soil in the intervening paths are estimated, these values can be used to create models of radiation intercepted by a row crop. This approach is an oversimplification, however, because real canopies, even those of broad-leaved herbaceous crops such as potatoes–in which in-row canopy cover viewed from above during peak foliar growth can be close to 100 percent– are not homogeneous. Therefore, it may be necessary to incorporate a correction factor to the model results.
In addition, the type of light that intercepts vegetation should be considered. Solar radiation is a combination of direct radiation from the sun and diffuse (scattered) radiation. Furthermore, light that goes through a canopy has two components: unfiltered radiation that has passed through canopy gaps, and filtered radiation, which has been absorbed, reflected, or scattered by foliage.
The main objective of the study reported here was to evaluate potato row orientation, north-south, northwest-souteast, northeast-southwest, and east-west for best production and economic return; alternately, to determine if one or more directions should be avoided when growing potatoes in the northern hemisphere. Row orientation and direction of planting will be used synonymously throughout the remainder of this report.
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