Ill. Admin. Code tit. 8, § 900.813 – Phosphorus Based Application

a) If the average Bray P1 or Mehlich test result for soil phosphorus calculated from samples obtained from the application field is 300 pounds or less of elemental phosphorus per acre, livestock waste may continue to be applied to that field in accordance with subsection (f) of Section 20 of the Livestock Management Facilities Act [510 ILCS 77/20(f)] and this Subpart. [510 ILCS 77/20(f)(3.6)]
b) If the average Bray P1 or Mehlich test result for soil phosphorus for an application field is greater than 300 pounds of elemental phosphorus per acre, the owner or operator shall apply livestock waste at a rate not to exceed the phosphorus maintenance fertilizer rate to the field pursuant to subsection (c) of this Section, until the average Bray P1 or Mehlich test for soil phosphorus indicates there is less than 300 pounds of elemental phosphorus per acre. [510 ILCS 77/20(f)(3.6)]
c) If a phosphorus application rate is required for a field, the plan shall be amended by the owner or operator for that field to determine the maximum livestock waste application rate. The amendment to the plan for that field shall contain the following:
1. 1) The phosphorus content of the livestock waste, expressed as P₂O₅, derived from MidWest Plan Service's MWPS-18, Livestock Waste Facilities Handbook (Table 2-1, 10-6, or 10-7), 35 Ill. Adm. Code 560 (Table 1 or Table 2), or the results of analysis performed on samples of waste;
2. 2) The targeted crop yield goal of each crop in the field, obtained pursuant to Section 900.807 of this Subpart;
3. 3) The phosphorus maintenance fertilizer amount, expressed as P₂O₅for the targeted crop yield goal of each planned crop, obtained from the Illinois Agronomy Handbook; and
4. 4) The maximum livestock waste application rate, calculated from the items in this subsection (c), for each planned crop.