Agricultural Order 4.0
Ag Order 4.0 requirements apply to owners and operators of irrigated land used for commercial crop production on the Central Coast
About the Ag Order 4.0
The Central Coast Regional Water Quality Control Board (CCRWQCB) recently approved the new Ag Order 4.0 that will affect several different aspects of agricultural production including protecting riparian and wetland habitat, discharge of pesticides to surface waters, sediment discharges to surface waters, and most importantly minimizing nitrate discharges to groundwater and nutrient discharges to surface water. This article focuses on the impacts of Ag Order 4.0 on the use of nitrogen (N) fertilizers.
Why is this Important?
The Ag Order 4.0 sets limits on how much nitrogen is being discharged using the formula A-R, where ‘A’ is the amount of nitrogen that is applied and ‘R’ is the amount of nitrogen removed in pounds per acre per year.
The applied nitrogen ‘A’ could come from different sources - N applied in fertilizer (A-fertilizer), N applied in irrigation water (A-irrigation), N applied in compost (A-compost) and N mineralized from organic fertilizer (A-organic fertilizer).
The removed nitrogen ‘R’ from an acre of land could happen due to different reasons - N removed from the field by the crop (R-harvest), scavenged during the winter fallow by cover crops or immobilized by high-carbon compost (R-scavenge), N removed by denitrification bioreactors (R-treated), N sequestered in woody plant biomass (R-sequestered), or other unspecified forms of N removed from fields (R-other).
A-R Limit/Target = N applied to the field (A) - N removed from the field (R)
A = A-fertilizer+ A-organic fertilizer+ A-irrigation+ A-compost
R = R-harvest + R-scavenge + R-sequestered + R-treated + R-other
Ag Order 4.0 sets deadlines by which growers would have to comply with the A-R limit requirements for the next 30 years (Table1). These compliance dates can be used as a countdown to when growers would need to improve their N use efficiency practices. In order to meet the A-R limit requirements, three nutrient management practices that growers can follow to improve N use efficiency are: 1) Account for residual soil nitrate levels before developing a crop nitrogen management plan, 2) Account for nitrate levels in your irrigation water in your crop nitrogen management plan, 3) Adopt efficient irrigation management practices and minimize or limit loss of nitrogen past the crop root zone.
Table 1: A-R Regulatory Schedule
Regulatory Status
(Target/Limit)
A-R Limit
(Lb of N/ac/year)
Compliance Date
(By Dec 31)
Target
Target
Limit
Limit
Limit
Limit
Limit
500
400
300
200
150
100
50
2023
2025
2027
2031
2036
2041
2051
