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ARS Home » Research » Publications at this Location » Publication #89936
Title: HYDROLOGICAL COMPONENTS OF A YOUNG LOBLOLLY PINE PLANTATION ON A SAND SOIL WITH ESTIMATES OF WATER USE AND LOSS

Author
item STARK, DEBORAH
item DOUGHERTY, P - WESTVACO FOREST RESEARCH
item ZARNOCH, S - USDA FOREST SERVICE, SRS

Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: Loblolly pine is a major commercial tree species in the southeastern United States. Water stress is one of the factors that imposes limits to forest productivity. Irrigation and fertilization can rapidly increase canopy cover, basal area and other stand characteristics such as tree height. As the canopy develops, more rainfall is intercepted and limits the amount of water that gets through the canopy to the soil. The productivity of pine stands must then depend in part on the stand's ability to acclimate to changes in soil water availability, especially during the growing season. Understanding how rainfall interception and soil water are affected by fertilizing and irrigating a young pine stand and how the growth induced by these treatments affects water availability was the objective of the hydrological component of this study. We found that there were no significant differences in the amount of leaf area produced or the amount of stem basal area between the treatments that were fertilized and those that were irrigated and fertilized. There must have been enough soil water in the top 1-meter of soil where the majority of the roots were to meet treatment growth demands without irrigating. The most productive unirrigated (fertilized-only) treatment did not require more water for greater production than its irrigated counterpart. Excess water from irrigation was evaporated from leaf and stem surfaces, drained to depths below 1 meter in the soil, or was used for energy exchange to cool the plant.

Technical Abstract: Fertilizer and irrigation treatments were applied in a 7 to 10-year-old loblolly pine (P.taeda L.) plantation on a sandy soil near Laurinburg, North Carolina. Rainfall, throughfall, stemflow, and soil water content were measured throughout the study period. Monthly interception losses ranged from 4 to 15% of rainfall. Stemflow ranged from 0.2 to 6.5% of rainfall. Rainfall, leaf area index (LAI), basal area (BA) and the interactions of rainfall with LAI or BA influenced prediction models of throughfall, but not stemflow on a stand level. We found significant differences due to treatments effects in the soil water of the top 0.5- and 1-meter soil layers by the beginning of the second growing season and throughout the remainder of the study period. Average daily water use and loss from a 1-m soil layer reflected the low water-holding-capacity of the coarse sand. Infiltration rates were greatest during periods of moderate to heavy rainfall. Soil water in a 1-m layer was rapidly depleted to within 10% of available water during periods of little or no rainfall. Irrigation did not significantly effect productivity and created a greater potential for loss of water to drainage below 1 m. Based on Zahner's (1966) method of soil water depletion in a sandy soil under forest cover, total drainage to below 1 m was 55% of evapotranspiration in unirrigated plots and 150% of evapotranspiration in irrigated plots.