Less than 2,000 acres of carrots are produced in Arizona (Figure 3-9-1). Seasonal nitrogen (N) accumulation by carrots is approximately 210 lbs N/acre, and amounts removed in the harvested roots is approximately 160 lbs N/acre (12, 13). Depending on residual soil nitrate, carrot yields are usually maximized at less than 250 lbs N/acre.

Pre-plant N applications should be based on a pre-plant nitrate-N test, and recommended rates will vary from 10-40 lbs/acre, depending on soil test levels and rates of monoammonium phosphate (MAP) applied as a pre-plant phosphorus (P) fertilizer (Section 2.1). The N can be applied with the pre-plant P fertilizer. Alternatively, early-season N might be applied through sprinklers if used for irrigation.

If carrots are furrow irrigated and most in-season N application is by side dress application, the N rate to be applied at side-dress should be based on a pre-side dress nitrate-N test. The required application rate depends on the difference between the minimum required threshold of 30 ppm and the measured soil test level. Approximately 4 lbs of N/acre need to be added to increase the soil test nitrate-N by 1 ppm. Fertigation in furrow water later in the season should only occur if soil nitrate-N levels fall below 20 ppm.

Most carrots in Arizona are currently produced under season-long sprinkler irrigation. These systems allow for a more frequent, lighter application of N that is more in line with anticipated crop N uptake. Seasonal N rates can be adjusted based on results of in-season soil nitrate-N tests. The guideline considers a soil nitrate-N test level of 20 ppm as the lower threshold below which N fertilizer application is required. N fertilizer needs to be applied at a rate of 4 lbs/acre to raise the soil nitrate-N level by 1 ppm. 

Based on recent studies in Central Arizona, carrots have not responded to P fertilizers when Olsen P soil tests are greater than 20 ppm (Table 3-9-1). Carrots are planted in late fall, and response to a starter P fertilizer can occur.

Carrot yield response to K fertilization has not been observed in Arizona. However, it is prudent to occasionally run AA soil tests to verify that K levels are greater than 150 ppm and conduct occasional tests of leaves to verify that K concentrations are above 2.5% (Section 4.3). 

As of the writing of these guidelines in 2024, a response to Zn fertilizer in carrots has not been observed as it has in other vegetables. Nevertheless, soil DTPA Zn levels and leaf tissue Zn concentration should be monitored if natural soil levels become depleted (Sections 2.5 and 4.3).