- Author: Richard Smith
Coping with Rising Fertilizer Prices
Richard Smith and Michael Cahn, UCCE Farm Advisors, Monterey County
Growers have been affected by a near doubling in fertilizer prices between the summer of 2020 and the end of 2021. The last time that fertilizer prices had a similar spike was in 2008 (Figure 1). In a recent article in Agricultural and Resource Economics published by the Giannini Foundation of Agricultural Economics at UC, Davis, Aaron Smith discussed details in global dynamics in production and demand of fertilizers that are affecting this surge in prices (https://s.giannini.ucop.edu/uploads/pub/2022/02/24/v25n3.pdf ). The forces that he described not only affect nitrogen but phosphorus and potassium fertilizer prices as well.
Figure 1. Trend of fertilizer prices over the past 30 years (DAP = diammonium phosphate)
The United States produces about 85% of the ammonia and 90% of the phosphate rock that it uses, both of which are mostly used to make fertilizers. However, we import 90% of the potash used. Domestic production of ammonia declined from 2000 to 2010 when natural gas prices were historically high. But after 2010, the use of hydraulic fracturing (fracking) increased the supply of natural gas and lowered the cost of production (but not necessarily the price of natural gas!). Aaron explained that supply side factors such as the price of natural gas, inclement weather events, COVID disruptions and shipping costs do not fully explain the sustained increase in fertilizer prices over the past 2 years. On the demand side corn, soybean and wheat prices increased 60% from the summer of 2020 through the end of 2021 which may have incentivized growers to apply more fertilizer which put pressure on fertilizer prices. These cost increases predate the Russian invasion of Ukraine, and at present, the war has not increased fertilizer prices further, but that situation could change.
Central Coast growers are facing increased fertilizer prices and are looking for ways to reduce the use of fertilizers. In high value horticultural crops, fertilizer costs typically represent a smaller portion of production costs than they do for agronomic crops. For instance, in the 2019 romaine hearts cost study conducted by Tourte et al, fertilizer costs represented 8.5% of total crop production costs. However, in light of current price spikes, fertilizer prices have become more significant.
Over the past 25 years we have been evaluating practices to improve the efficiency of applied nitrogen mostly with an eye to helping growers comply with water quality regulations. We have reported the results of our research at many meeting, articles and blog entries. However, we will revisit one study that we did in 2019 which illustrates the following concepts: 1) careful monitoring residual soil nitrates and accounting for them in making fertilizer application decisions, 2) careful irrigation water applications to reduce nitrate loss. These are the two key practices that can help growers efficiently manage nitrogen applications and minimize over application that is now so costly.
In 2019 we conducted a trial with a cooperating grower to evaluate water and nitrogen management of romaine lettuce. We split the field in half and on one side of the field irrigation and fertilizer decisions were guided using the CropManage decision support tool (cropmanage.ucanr.edu). The other half of the field was managed according to grower's standard practices.
Irrigation details: Romaine lettuce was germinated using subsurface drip buried at a 3 to 4-inch depth in the center of 40-inch wide beds. Flowmeters were installed to monitor irrigation on both the CropManage and grower standard treatments. Similar volumes of water were applied to in both treatments during germination/stand establishment: CropManage = 3.4 inches, grower standard = 3.7 (Fig. 2). After thinning, until harvest different amounts of water were applied to the two treatments. The ideal amount of water recommended by CropManage was 3.8 inches of water. CropManage bases the recommendation on reference evapotranspiration data (ET) from the nearest CIMIS weather station, a crop coefficient model based on canopy development, and considerations of the application uniformity of the irrigation system. In the grower standard practice 3.3 inches were applied and in the CropManage treatment 3.8 inches were applied.
Nitrogen fertilizer: Twenty gal/acre of 5-20-0 were applied to both management practices at planting as an anticrustant/starter fertilizer. Soil nitrate was monitored in the upper foot in both management zones at regular intervals during the season (Fig. 3). Soil nitrate levels were moderate at the thinning (< 15 ppm NO3-N) and fertilizer was added to both management systems. The big difference between nitrogen management between the CropManage and grower standard treatments was the mid-October fertilizer applications. In the CropManage treatment we made a more moderate application in early October because soil nitrate levels were still moderately high (18 ppm NO3-N). Later we applied a 4th application of nitrogen fertilizer through the drip system (39 lbs N/acre) to supply sufficient N to match crop uptake demand until harvest. In contrast, the grower standard practice applied 91 lbs N/acre through the drip system as a 3rd and final application in mid-October. Total N applied to the CropManage treatment was 129 lbs N/acre and to the grower standard treatment was 191 lbs N/acre (Table 1).
Harvest: Commercial yields evaluations were made in adjacent 12 bed-wide strips (by the length of the field). Carton yield (lbs/acre) was about 5% higher in the CropManage area (Table 1) although cartons per acre were 3% higher in the grower management zone due to a higher final plant population (Table 2). Disease pressure from INSV and Sclerotinia caused plant loss and affected the final plant populations in the management zones. Net carton weight of the grower standard area averaged 2.4 lbs per box less than the CropManage area and plant tissue had a lower water content than the CropManage treatment (Table 1). The higher plant weight and water content measured in the CropManage area (Table 2) may be due to the extra water (0.5 inches) applied to this treatment during the final few weeks of the crop. In contrast, the extra nitrogen (90 lbs/acre) applied to the grower management area did not increase plant weight and growth relative to the CropManage area.
Take Home Message: Over the years we have conducted many side-by-side evaluations comparing grower standard practices with improved efficiency practices guided by the CropManage decision support program. In this example, both management treatments applied close to the recommend amount of water to avoid leaching of nitrate during the production season. The soil nitrate evaluations indicated that only moderate amounts of N were needed at each fertigation; in addition, adding one extra fertigation event in the CropManage treatments improved the ability to precisely manage what the crop needed. The high final fertilizer application on the grower treatment did not improve yields and resulted in more residual nitrogen in the soil at the end of the season. The bottom line is that careful irrigation scheduling and monitoring of soil nitrate helped reduce nitrogen fertilizer applications in this study and safeguarded yields. If you need assistance in implementing better water and fertilizer nitrogen management practices on your farm, please give us a call. We are available to consult with you.
Table 1. Applied water and nitrogen fertilizer, and commercial yield from strip plots on November 6, 2019.
Table 2. Nitrogen content, untrimmed plant weight, dry matter content, and plant population from strip plots on November 5, 2019.
Figure 2. Applied water for CropManage and Grower Standard areas.
Figure 3. Applied fertilizer nitrogen and soil nitrate concentration in the 0 to 1-foot depth.