Nutrient Management Workbook

Guide to Completing the Workbook - Sections A to S

This workbook is organized in sections, from A to S, with each line of the Worksheet corresponding to the detailed descriptions found here help you develop the required information.

Section O - Nitrogen Index

The Nitrogen Index is a tool for limiting nitrate nitrogen movement below the root zone in agricultural fields. It assesses the vulnerability of nutrient management practices with respect to the movement of nitrates in groundwater and is based on nutrient management practices and characteristics of the soil.

The Nitrogen Index must be completed when there is nitrogen remaining over the winter season:
1) When the Agronomic Balance exceeds 17 kg/ha (15 lbs/ac) or
2) When Section N has been completed.

To calculate "Value A₁" (nitrate remaining after harvest) take "Previous Crop" (from Section A) and go through steps J through M (or use Crop Removal Balance - Line M - from previous year's nutrient management plan).

Add the values from each section to get the total N-Index

	Value A2 _________ (Line M from Current,Crop - to use in next year's plan	Value A1 or A2 cannot exceed the Maximum N-Index Value from Table 14 for the Hydrologic Soil Group
		A high Value A2 could be limiting to next year's fall manure application rate.

For all crops, use Table 13 below to calculate the Nitrogen Index (N-Index). Because the N-Index is targeting nitrogen leaching during the winter following crop harvest, the Value A₁ or A₂ refers to the crop removal balance calculated for the crop just harvested, while Value B refers to the N available for loss from manure applied after crop harvest.

Determine the Hydrologic Soil Group Category for the field from the soil types (soil series names) present in the field. Hydrologic soil groups corresponding to the various soil series names found in Ontario are listed in Table 17, or in the Drainage Guide for Ontario (OMAF Publication 29).

Where a field has more than one soil series, pick the soil in the hydrologic group that is most vulnerable to leaching (i.e. soil group A) or the dominant soil series if it represents more than two thirds of the field).

Determine the Maximum N-Index Value for the Critical Hydrologic Soil Group for the field from Table 14, below:

Example:

Section N: Since the application rate exceeds 5000 gal/ac, (from Table 11) Section N must be completed.
41 lbs/1000gal total N divided by 1000 (to give lb/gal) x 5500 gal/ac x 0 .4 (from Table 12) = 90 lbs/ac potential N loss

Nitrogen index : The maximum allowable N-Index is 4 for a Guelph Loam (hydrologic soil group B from Table 14). In this example the N-Index is: (Value A ) 0 + (Value B) 6 = 6

Therefore other management options must be considered. Alternative options include a cover crop, adjusting the application rate or timing of the fall applied manure.

If a red clover cover crop were planted or manure application was delayed to late fall, then the N available for loss would change from 90 to 45 lbs/ac and the Value B would be 3.

(41 lbs/1000gal total N divided by 1000 (to give lb/gal) x 5500 gal/ac x 0 .2 (from Table 12) = 45 lbs/ac potential N loss)

Nitrogen Index : The maximum allowable N-Index is 4 for a Guelph Loam (hydrologic soil group B from Table 14 ). After management changes in the example the N-Index is: (Value A₁) 0 + (Value B) 3 = 3 The planned application of manure with a fall cover crop of red clover meets the Nitrogen Index requirements.

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