Note: This is part of a Research Update series that highlights projects funded by the California Department of Food and Agriculture (CDFA) Fertilizer Research and Education Program (FREP) annual Grant Program.
Project Title: Enhancing Nitrogen and Water Use Efficiency in California Carrot Production Through Management Tools and Practices
Project Leader: Ali Montazar, Irrigation and Water Management Advisor, University of California Agriculture and Natural Resources (UCANR)
Project location: Imperial and Kern Counties
Project Status: Complete
Overview
The purpose of this project was to understand the viability and applicability of current nitrogen and irrigation management practices in California carrot production. The project aimed to develop knowledge and information on improving and promoting adoption of management practices that optimize nitrogen and irrigation water use efficiency in addition to developing new information on nitrogen (N) uptake curves, net N removal, and crop water use. Data from the project was also used to add carrots to CropManage, a web-based tool for water and N management.
Highlights
- Carrots are typically over-irrigated during plant establishment.
- N uptake curve was developed for desert carrot; 50% of N uptake occurs between 80-130 days after seeding.
- N application rates greater than 145 pounds per acre do not have a significant impact on carrot root yield in a well-managed irrigated field.
- CropManage carrot module was developed and evaluated for carrot fields in the low desert region.
- An average N removal of 3.0 pounds per ton of fresh carrot root was determined for desert carrots.
Background
California fresh market and processing carrots comprise an area of 60,300 acres with a total value of nearly $685 million per year. Currently, lack of sufficient information on efficient water and N management practices is one of the largest uncertainties faced by carrot growers, hindering efficient resource-use and possibly compromising the economic sustainability of production in the face of increasingly limited and costly water and fertilizer supplies. The industry is being held responsible for determining what the most efficient nitrogen fertilization rate is, and there is high value in maintaining regulatory compliance. Therefore, information on irrigation and N uptake specific to California conditions are urgently needed.
Approach
Researchers conducted three-year field experiments at the UC Desert Research and Extension Center and 20 commercial fields in Imperial and Kern counties to examine different N and irrigation application strategies. Extensive field measurements included soil nitrate content, total N content in carrot tops and roots, actual consumptive water use, and canopy coverage. In addition, determinations of fresh and dry weights of roots and foliage were made on a monthly basis throughout the season.
Image 2 and 3: A multi-depth soil moisture sensor monitoring station equipped with Tule sensor in commercial sites (left) and fully automated evapotranspiration (ET) tower (right).
Project findings: Irrigation Management
Carrots are typically irrigated every other day for two weeks after seeding in the desert to keep the beds moist and prevent crusting. A comparison between the averages of applied water and actual consumptive water use for a 30-day period after seeding suggested that carrots are over-irrigated during plant establishment. An average of 3.8-in was measured as actual consumptive water use for this period across the experimental sites (Fig. 1), while the applied water varied from two to three times this amount.
Sites had variable actual consumptive water uses depending upon early/late planting, irrigation practice, length of crop season, soil type, and weather conditions. The seasonal crop water use of fresh market carrots is nearly 16.0-in for a typical crop season of 160-day with planting in October. In the desert region, approximately 50% of crop water needs occurred during the first 100 days after seeding and the other 50% during the last 60 days before harvest for a typical 160-day crop season (Figure 1 and Table 1).
The critical period for irrigation is between fruit set and harvest during which the water stress should be avoided. In addition, sprinkler irrigation may be considered as a more effective irrigation tool when compared with furrow irrigation due to more frequent and light irrigation events made possible by sprinkler irrigation. Sprinklers also reduce salinity issues, which is important since carrots are very sensitive to salt accumulation.
Fig. 1. Cumulative actual crop water consumption (actual ET) at each of the experimental sites in the desert region.
| 21-22 season | 22-23 season | |
| N application (lb. N/ acre) | N1=140 | N1=145 |
| N2=185 | N2=180 | |
| N3=235 | N3=217 | |
| Water application (in) | I1=24.5 | I1=23.6 |
| I2=30.8 | I2=29.7 |
Project Findings: Nitrogen Management
Small gradual increases in N contents of roots were observed until about 65 days after seeding (DAS). This suggested that N begins to accumulate at a rapid rate between 65 and 80 DAS; however, the period of rapid increase could vary depending on early (September) or late (November) plantings. The N uptake curves suggested that nearly 50% of the total N was taken up between 80-130 DAS (Fig. 2). This 50-day period appears to be the most critical period for N uptake, particularly in the storage roots. Thus, proper N fertility in the effective crop root zone is essential during this period.
Fig. 2. Nitrogen accumulation trends in storage roots, tops, and total (plants) over the growing season at the experimental sites.
Within the range of N application rates examined there was no significant effect of N rate on total N uptake and the N accumulated in roots. The results suggested a positive effect of N application on carrot yield; the N application rate had a clear and significant effect on increasing aboveground foliage (tops), which could be a reason for greater nitrogen uptake at the higher rate of N applied (Fig. 3).
Fig. 3. Mean fresh carrot root yields as affected by water regimes and nitrogen (N) application rates over the study seasons. The bars show standard error of root yield values. Different letters show significant difference (p < 0.05) by Tukey’s test. N1, N2, and N3 are applied N at 140, 185, and 235 pounds per acre, respectively; I1 and I2 are applied water at 24.5 and 30.8 inches, respectively.
Sufficient N availability in the crop root zone over the growing season and the lack of significant yield response to N application rates demonstrates that optimal N rates could likely be less than the applied amounts in most sites.
Conclusions
The study results clearly demonstrated that carrot fields had variable consumptive water use, depending on early/late planting, cultivars, irrigation practices, length of crop season, soil type, and weather conditions. Sufficient N availability in the crop root zone over the growing season and lack of a significant yield response to N application within the range of N application rates suggested that N optimal rates could be likely less than the applied amounts at most sites. Since residual soil N contribution can be considerable in carrots, a pre-plant soil nitrate-N assessment, down to a 60 cm depth, can be a tool that enables farmers to improve N management and maximize yield and quality while minimizing economic and environmental costs. Growers are encouraged to try using a reduced N rate (10-20% lower than their current practice) on a small field to evaluate how it fits their specific farming practices before they adopt it on a widespread basis. Utilizing the information developed by this study on crop N uptake, net removal rates, and crop water use may have a significant impact on water quality as well as soil water and N availability, potentially increasing the economic sustainability of carrot production in a region where irrigation water will become less available or more expensive.