By design, SISC's initial suite of metrics addresses some of the most critical areas impacted by the production of fruits, vegetables and nuts.
The brief metric summaries, below, include both the rationale for inclusion and a technical overview. For detailed information, including technical material and supporting guidelines, please login at left to visit the "General Information" and Metrics" pages.
Applied Water Use Efficiency
Water is already in short supply in parts of the world and will become increasingly scarce as populations increase and climate change continues to alter weather patterns. In many places, water is also getting more expensive. Efficient irrigation is a critical component of sustainable crop production.
The Applied Water Use Efficiency metric measures the total amount of applied water used to produce the crop. Note: a second metric, in development but not yet finalized, is Simple Irrigation Efficiency, which measures the amount of water applied to the crop relative to the crop’s water need resulting from transpiration and soil evaporation (ETc).
Crop production requires a substantial amount of fuel and electricity to power farm machinery and irrigation. In addition, a sizeable amount of energy is required to produce fertilizers, particularly those containing nitrogen. Energy production is resource-intensive regardless of the production method. As energy costs rise, it will be critical to track agriculture's use of energy.
The Energy Use metric includes direct energy from fuel and electricity and indirect energy in the form of energy required to produce fertilizers (“embedded energy”). Because growers of multiple crops often do not know how much fuel and electricity was used any particular crop, we have developed a tool to help allocate data to a particular crop or management area. This may also be useful to growers of a single crop who would like to estimate energy use by field.
Nitrogen is a key nutrient for crop production. However, when transported off the farm, it poses an economic loss to the grower and can have detrimental impacts to surface and groundwater quality. Nitrogen lost to the atmosphere as nitrous oxide (N2O) is a potent greenhouse gas, with ~300 times the warming potential of carbon dioxide (CO2). Both nitrogen and phosphorus were chosen for the nutrient metrics as they are widely recognized as pollutants and are a higher priority for environmental improvement than potassium (see also: Phosphorus Use metric).
The Nitrogen Use metric aims to capture the most significant sources of nitrogen being added to the farm system. It includes nitrogen from synthetic and organic fertilizers, nitrates dissolved in irrigation water, and nitrogen fixed from the air by leguminous crops. By accounting for all of these significant sources of nitrogen, a grower should be able to increase the efficiency of nutrient use in crop production.
Phosphorus (P) is a key nutrient for crop production. However, when transported off the farm, it poses an economic loss to the grower and can negatively impact surface and groundwater quality. Both nitrogen and phosphorus were chosen for the nutrient metrics because they are widely recognized as pollutants and are a higher priority for environmental improvement than potassium (see also: Nitrogen Use metric).
The amount of phosphorus that plants can access in soil varies widely. Good stewardship includes taking advantage of existing soil P reserves before adding more P fertilizer.
The approach taken in the Phosphorus Use metric differs from that of the Nitrogen Use metric because the two elements behave differently in the environment. Nitrogen is much more mobile than phosphorus; in contrast, most forms of P are less soluble than nitrate and P has no significant gas phase.
The Phosphorus Use metric takes advantage of the fact that when labs return results of P tests to growers they also offer recommendations for how much P a grower should apply. These recommendations are based on several factors, but a major determinant is the amount of P already available in the soil. The metric, therefore, looks at how much P the grower has applied above that recommended value.
Soil Organic Matter
Soil Organic Matter (SOM) is the organic fraction of soil excluding non-decomposed plant and animal residues. SOM is usually measured by the amount of Total Organic Carbon (TOC) present in the soil. Increasing amounts of SOM, and hence organic carbon, provide significant agronomic and environ-mental benefits including improved nutrient delivery to plants, water retention, drainage, and resistance to disease and erosion. A soil’s ability to store SOM varies greatly depending on climate, soil texture and soil type. To normalize against this variability, SOM is compared with a site-specific estimate of the soil’s potential to hold SOM.
The Soil Organic Matter metric is the measured TOC of the soil divided by that soil’s potential to store organic carbon, as modeled using USDA’s Soil Management Assessment Framework (SMAF).
>> To learn about metrics in development, click here.
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