On Dec. 13, 2011, the USDA announced revisions to the national conservation practice standard on nutrient management, code 590. See revisions.
The goals of the revisions are to better assist producers in managing and applying nutrients. The expected outcomes are improved returns on nutrient investments and protection and/or improvement of water, air, soil and overall agricultural sustainability. The revisions are seen as an endorsement of the 4R Nutrient Stewardship concept which takes into account social, economic and environmental factors in the context of determining the right source, rate, time and place for a nutrient addition. The 4R concept was developed through a partnership of the International Plant Nutrition Institute, The Fertilizer Institute, and the Canadian Fertilizer Institute (www.ipni.net).
Breaking down the 4R’s
The right source means identifying the best fertility source or combination of sources (commercial fertilizer, manure, etc) that meet the crop needs and are appropriate for the specific location. Factors to consider when determining the right source include:
- Soil conditions and properties
- Fertilizer delivery and application issues
- Environmental Risks
- Economic constraints e.g. price and application costs
The right rate is determining your nutrient requirements to achieve your production goals. Present crop, crop history, soil test, and in-season nutrient testing all provide information that should be utilized in determining fertility requirements. Additional factors to consider in determining the right rate are:
- All 17 essential nutrients must be present
- A deficiency in one nutrient cannot be overcome by applying an excess of another nutrient. A crops yield is determined by the most limiting nutrient (Liebig’s law of the Minimum)
- Match nutrient supply with plant requirements
The right time means ensuring that the nutrients are available to meet the crop demand. Strategies to ensure nutrients are available when plant nutrient demands are high include strategies such as split nutrient applications over the growing season, and use of controlled release fertilizers. Additional factors to consider in determining the right time are:
- The availability characteristics of the nutrient source
- Sight specific conditions such as soil characteristics
- Weather and other environmental conditions
The right place means ensuring that nutrients are located and retained where they are accessible to the plant. Nutrient placement decisions such as injecting, banding or incorporation need to take into account the crop, soil properties and cropping system and must be balanced with soil erosion goals. Additional factors to consider in determining the right place are:
- The fertilized soil volume (concentration)
- Relation to the plant root system.
- P and K move to plant roots primarily by diffusion
- Plant nutrient demands are greatest during rapid vegetative growth