Abstract
The dairy industry in Idaho (ID) has expanded rapidly in the past 30 years. The expansion of the dairy industry has brought nutritious food and drinks across the U.S. and world and substantial agribusiness opportunities, especially in Southern ID. The dairy is, as of 2023, the largest industry regarding cash receipts in the ID agricultural economy. Development of the dairy sector has not only increased revenues for the direct participants in the dairy supply chain, but also aligned sectors such as production of feed crops, including alfalfa hay and corn silage. Despite these benefits, the dairy industry also produces substantial amounts of dairy manure, and management of dairy manure is a considerable cost for dairy producers. Manure contains large amounts of nutrients, but the local demand for crops may not be able to absorb all of the supply, especially in major dairy producing regions in Southern ID. In addition, the increase in population and associated increase in land conversion for housing and other commercial development in some regions of ID in recent decades has led to reductions in cropland areas for feed and other crops, which has provided fewer outlets for distributing manure-based nutrients. The associated potential decrease in nutrient demand from cropland can intensify the oversupply of nutrients in some regions. An oversupply of manure can cause nutrients to accumulate in the local environment, which can contaminate soil, water, and air greenhouse gases. While the nutrient oversupply can be detrimental to the local environment, the extent of the impact regarding the total quantity and distribution of manure-based nutrients remains unclear.
In this thesis, dairy manure nutrient supply-demand balances in ID were quantified for the observation period of 1990 – 2022. The first set of quantification analyses is done at the state, region, and county-levels to determine the regional distribution of dairy manure in the state. A second analysis, which focuses on the more localized distribution of dairy manure and cropland, relies on a unique dataset from the Idaho State Department of Agriculture that allows for determination of the locations, sizes, and dates of establishment of ID dairies. In this more spatially targeted analysis, supply-demand balances were estimated at the census tract level for three major dairy producing counties in Southcentral ID (Gooding, Jerome, and Twin Falls) for the period of 2007 to 2022.
The results from the quantification analysis show that the state-level supply-demand balance has increased rapidly for all analyzed nutrients over the course of 1990 to 2022. In addition, the increase in nutrient balance has mainly occurred in Southcentral and Southwest ID, where most of the dairy farms have been established over this observation period. The spatial analysis demonstrates that the most acute increase in the manure-based nutrient supply has concentrated near rivers, including the Snake River, to a relatively higher degree than other census tracts. As time has passed, the number of dairies, and associated manure-based nutrients, further away from the Snake River has also increased. This has led to a substantial accumulation of nutrients in some areas that had previously not had much manure present. In some census tracts, as of 2022, the amount of nutrient accumulation was estimated at 10 times larger than in 2007. However, years of substantial amount of nutrient accumulation, and corresponding reduction in pace of dairy industry expansion, has caused nutrient accumulation to increase at a decreasing rate in more recent periods. Due to the chemical characteristics of liquid and solid manure, there has been greater increases in supply and accumulation of Nitrogen than Phosphorus and Potassium. Composting decreases Nitrogen relative to Phosphorus and Potassium, and dairies and industry partners currently compost about half of the dairy manure in Southern ID.
The main result of this thesis is that the substantial expansion of the dairy industry has led to a large accumulation of dairy manure nutrients in Southern ID. Further development of manure-based fertilizer product industries, which can implement value-added processes that extract the water and concentrate nutrient solids from liquid and solid dairy manure, and, hence, reduce the transportation costs to ship the manure-based nutrients away from the dairies, can help reduce the nutrient oversupply in the future. Such development can also potentially facilitate shipment of manure-based fertilizer across the Western U.S., helping both dairies via a diversified revenue stream as well as specialized manure processing businesses to generate profits from related businesses. This can also help remediate environmental issues, including reducing contamination of soil, water, and air and release of greenhouse gases. Reducing the environmental impact of the dairy industry can both ensure that agricultural productivity is sustained and help ensure that the ID agricultural economy remains vibrant in the future.