USDA-ARS

Idaho is the third largest milk producing state in the U.S., housing approximately 650,000 milk cows and an equal number of young stock, with the majority of these cows located in southern Idaho’s Snake River Valley region. The manure generated from dairy production in the region is used as a nutrient source in cropping systems. Due to the high transport cost of manure, land near the dairies tends to receive higher rates of manure which can lead to nutrient imbalances, particularly phosphorus.

Manure treatment technologies, such as anaerobic digestion, flocculated solids, solid-liquid separation and advanced treatment systems, can all help produce nutrient-rich manure-based fertilizers that are more stable and less expensive to transport than fresh manure. These products could enable producers to expand the land on which manure nutrients are applied and improve the sustainability of the dairy industry in the region. To effectively utilize these manure byproducts, information related to nutrient content and availability as well as potential environmental risks needs to be assessed.

The Northwest Irrigation and Soils Research Laboratory is investigating the effects of two manure-based fertilizer products on nutrient cycling in soils and plants, crop yield, forage quality and greenhouse gas (GHG) emissions in semi-arid forage systems. The two products evaluated are solids from a flocculated solids treatment system and solids from an evaporation system. The goal is to provide producers with information and guidelines for use of these products in regional cropping systems.

The study consists of six treatments including one rate of each of the manure solids applied to soils that have either never had manure applied or have had a one-time heavy application of solid manure prior to application of the byproducts and control treatments (with and without solid manure application) that receive no nutrient inputs. The soils are Portneuf silt loams, which are the most common soil type in the dairy producing region. These soils are calcareous with a pH near 8.0. This is a semi-arid region with approximately 9 inches of rain each year, with the majority occurring in the winter, therefore irrigation is needed for crop production. The crop rotation consists of silage corn followed by a winter crop of triticale for four years followed by a year of alfalfa.

Figure 1: Randomized block design schematic

Data collected includes:

• Soil samples in the spring prior to planting to assess the fertility status of the soil.
• Soil cores (3’) which will be collected during select years to evaluate carbon and nutrients within the soil profile.
• Annual soil sampling to determine soil health status and changes over time in the top 12”.
• Intact soil cores (6”) and soil slakes will be collected in alternating years to evaluate changes in soil structure and aggregate stability.
• Measurements of soil hydraulic conductivity.
• Crop yield and plant samples are collected to determine nutrient content and quality of forages.
• GHG emissions measurements are made throughout the year (2x a week in the growing season and 1x during the non-growing season).

All soil and plant samples are archived at the research station.