D. S. Janik, Oahu County Water Quality Extension Agent, Hawaii Cooperative Extension Service, College of Tropical Agriculture and Human Resources (USDA Cooperating), University of Hawaii at Manoa, Hawaii.
The Kaiaka-Waialua Bay News is the official newsletter of the USDA Kaiaka-Waialua By Hydrologic Unit Area Project. The purpose of the Kaiaka-Waialua Bay News is to provide you with updates on projects, upcoming events, and research information. The Kaiaka-Waialua Bay News will also provide soil and water conservation ideas and measures, educational resources, and strategies for resource management and protection.
Kaiaka-Waialua Bay News is published quarterly by Hawaii Cooperative Extension Service with participation from USDA Soil Conservation Service, USDA Agricultural Stabilization and Conservation Service, and the West Oahu Soil and Water Conservation District. Distributed in cooperation with the U. S. Department of Agriculture in furtherance of the Acts of Congress of May 8 and June 30, 1914. Cooperative Extension Work in Agriculture and Home Economics, Noel P. Kefford, Director and Dean, Hawaii cooperative Extension Service, College of Tropical Agriculture, University of Hawaii at Manoa, Honolulu, HI 96822 USA. To cite this article use: Janik DS. Soil and Water Quality. Kaiaka-Waialua Bay News 94 Jun (3) 2: 1, 3]
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New and prospective laws and regulations directly affecting agricultural land owners/users are increasing. Most address environmental and/or ecological impacts of agricultural practices on water quality. In 1989, Congress tasked the National Research Council (NRC) of the National Academy of Science to reassess the science, technical tools and policies needed by farmers to successfully address anticipated impacts, regulations and laws. In this and the next issue of Kaiaka-Waialua Bay News we report their findings and what they mean to farmers, land users and owners.
NRC identified 4 key actions necessary to improve water quality: 1) improving soil quality; 2) increasing nutrient, pesticide and irrigation use-efficiencies; 3) increasing resistance to erosion and runoff; and 4) greater use of buffer zones.
Improving Soil Quality
Most agricultural efforts focus on improving soil productivity. But soil productivity is not the same as soil quality. NRC defines soil quality as the optimum capacity to promote plant growth, regulate the physical effects of heat, wind and rain, and attenuate the physical/chemical effects of pollutants. In the past, soil productivity was often maintained at the expense of other factors. Because of this, productivity is not necessarily a good indicator of soil quality (e.g. increasing amounts of nutrients, pesticides and water are sometimes used to maintain productivity in spite of declining soil quality). According to NRC, erosion, salinization, compaction, acidification and/or loss of biological activity are the principal indicators of declining soil quality. Dr. Samir El-Swaify of the University of Hawaii at Manoa (UHM) College of Tropical Agriculture and Human Resources (CTAHR) notes that Hawaiian watershed studies, including pineapple and sugarcane lands within the Kaiaka-Waialua Hydrologic Unit Area (KW HUA) Project, are in agreement. "Significant percentages of [KW HUA] land are estimated as having erosion rates greater than the maximum accepted tolerance level," said Dr. El-Swaify. "Only a few storm events are responsible for the majority of soil losses. Plantation (and especially pineapple) roads were especially important contributors."
According to NRC, erosion, salinization, compaction, acidification and loss of biological activity are equally important. Their combined effect is profoundly greater than the sum of their individual effects. Soil and water quality assessments need to become part of routine soil testing and reporting.
Nutrient, pesticide, salt and trace element use efficiencies are determined by total amounts applied, crop response, soil residuals after harvest, soil quality and movement. Increasing use efficiency generally involves reducing the total amounts of applied chemicals. However, residuals can be decreased by enhancing soil quality, timing applications to actual crop needs and growing of multiple crops with
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different residual uptakes. Movement is related to irrigation water volume, method and management. As irrigation water is used by crops and evaporates from fields, residual chemicals concentrate and buildup. "Advising farmers and the public on safe and efficient use of agricultural chemicals has been a major focus of CTAHR," says Dr. Carl Evensen, Assistant Extension Specialist in Environmental Quality. "Our newest emphasis is on low input/sustainable agriculture" including low/transitional/no pesticide and "organic" methods.
Erosion and Runoff Resistance
A time lag exists between field erosion and stream sediment deposition. Sediment deposits therefore reflect past rather than current erosion. Resistance is related to total volume and energy of field runoff, soil quality, effects of storm events and the presence or absence of field buffer zones. Natural or undisturbed ecosystems resist erosion primarily through biological control. In Hawaii, important changes occur in crop soil biota in response to erosion according to Dr. Russell Yost, UHM CTAHR. These changes can result in a further decrease in resistance, and further accelerate erosion.
Buffer (often called "riparian") zones are strips of managed grasses, riparian ("natural") or wetland plants. Buffer zones redirect runoff during storm events, and intercept or immobilize sediment and pollutants before they reach receiving waters. Buffer zones are especially important to Hawaii and KW HUA because [as mentioned earlier,] "a few storm events are responsible for the majority of soil losses," says Dr. El-Swaify. Buffer zones establish areas of soil capture and recharge. Buffer zones include inter-row, topsoil/subsoil, inter-crop, inter-field, field perimeter, and soil to water interfaces. Buffering ability is determined by soil quality, biological diversity and microbial metabolic diversity.
Improving soil quality, use efficiency, resistance to erosion/runoff, and use of buffer zones are the keys to soil and water quality management
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