Project at a Glance

Title: Atmospheric deposition to agricultural soil

Principal Investigator / Author(s): Mutters, Randal

Contractor: Statewide Air Pollution Research Center, UC Riverside

Contract Number: 93-334

Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Acid Deposition, Agriculture


Atmospheric deposition of acidic air pollutants is widely recognized as an important environmental process. Most available data indicate that current levels of acidic deposition in California are below the levels required to adversely effect the yield of agricultural crops. However, excessive deposition of nutrient ions to soil may predispose plants to injury from other abiotic and biotic stresses. It was unknown whether current levels of acidic deposition exceed the growth requirements for any essential plant nutrients. Therefore, the objective of the study was to equate annual fluxes of dry and wet deposition to the nutritional requirements of major crops.

Aerometric data from a previously completed Air Resources Board (ARB) project (No. A 132- I 49) was used to calculate atmospheric inputs and estimate regional-scale deposition flux across selected agricultural production areas in the State. Mean annual depositions of wet and dry acidic compounds from all monitoring stations were included in the data. Average fertilizer application rates were determined for 16 selected crops by agricultural region based on information from the University of California, Cooperative Extension Service. Typical amounts of nutrients taken up in the aboveground biomass on a seasonal basis were determined from published experimental results. Deposition fluxes were determined by using published specie- specific deposition velocities for dry compounds and using precipitation data for wet compounds For those agricultural counties where monitoring stations were present, acidic deposition data were used to calculate: (1) Total Annual Deposition (TAD) of nitrogen (N), sulfur (S) and calcium (Ca); (2) TAD as a percentage of the fertilizer applied and (3) TAD as a percentage of nutrients taken up during the growing season. Dry deposition data were available from only two stations near agricultural areas, Sacramento and Bakersfield. In those counties dry deposition was included in the seasonal totals.

The TAD of N ranged < 1 to 14.4 kg ha-1 on a county basis Statewide. The highest deposition occurred in Kern County and the lowest in the coastal counties of Monterey and Sail Luis Obispo. Atmospheric deposition of N as a percentage of the fertilizer applied by growers ranged from 0.2% to 28% for lemon in San Luis Obispo County and for grape in Kern County, respectively. In contrast, TAD represented only 0.2% to 16% of seasonal N uptake by crops. Where dry deposition data were available, it represented approximately 8% to 15% of the TAD. The TAD of S ranged from 0.4 kg ha-1 in Contra Costa County to a high of 2.4 kg ha-1 in Kern County. This represented as much as 18% of the seasonal nutrient uptake of S by lettuce in Kern County. Sulfur is not routinely added as a fertilizer by California growers. Therefore, TAD as a percentage of applied fertilizer was not calculated. Similarly, California soil generally do not require amendment with Ca. The TAD of Ca represented < 2% of the seasonal nutrient uptake of the selected crops in all counties. Of those species typically measured in dry and wet deposition, only N at a few locations may represent a potential contributor to excessive nutrient loading to soil in California.

For questions regarding this research project, including available data and progress status, contact: Research Division staff at (916) 445-0753

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