Nitrogen Availability from Potato-Processing Wastewater for Growing Corn

A line source sprinkler was used to irrigate corn (Zen ?nays L.) plots with potato (Soianum tuberosum L.)-processing wastewater in 1979, 1980, and 1981. Nitrogen applications ranged from about 4 to 600 kg/ha. Corn yields were measured for each row, the grain and stalks were analyzed for total N, and N uptake was calculated. The plots were split by years, one-third of the area was fertilized with wastewater 3 y, one-third 2 y, and one-third 1 y. This allowed evaluation of current and residual value of wastewater fertilisation. Corn responded well to wastewater fertilization, with N applications in the wastewater increasing corn yields with increasing increments of N up to about 200 to 250 kg/ha annually, and corn grain yields ranged up to about 12 Mg/ha. Yield comparisons were made with plots fertilized with ammonium nitrate fertilizer. We determined that potato-processing wastewater N was almost equal to ammonium nitrate N for growing corn. Wastewater applications that will apply approximately 200 to 250 kg Nibs annually should be optimum for growing corn on this soil. Wastewater N from potato processing has good residual and carry-over for 1 y but under conditions of this experiment did not carry over for more than 1 y. Whether the excess N was lost from denitrification or leaching was not determined. Additional Index Words: line source sprinkler, residual nitrogen, corn grain. Smith, J. H., and C. W. Hayden. 1984. Nitrogen availability from potato-processing wastewater for growing corn. J. Environ. Qual. 13: 151-156. Irrigating with food-processing wastewater for growing crops is an established practice used by a large segment of the food processing industry (2, 4, 5, 6, 7, 8, and 1 I). In many existing systems, emphasis has been placed on disposing of wastewater with maximum applications of both the wastewater and included plant nutrients. Large amounts of wastewater and nutrients from potato (Solanum tuberosum L.)-processing operations have been applied to land with up to 550 cm of water and 2550 kg N/ha in 1 y (10). These seemingly excessive applications have not always created groundwater pollution problems, but in some cases have promoted almost total denitrification because of the anaerobic conditions in the soil related to the high water applications and the high energy content of the organic constituents of the wastewater (9). Well-managed wastewater irrigation fields growing grass for hay or forage look good and yield well because of the heavy fertilization with wastewater nutrients. Consequently, there has been interest from farmers in obtaining wastewater for crop irrigation and fertilization in areas adjacent to fields already irrigated with wastewater. With this developing interest in utilizing wastewater for its nutrient value, a need was seen for evaluating potatoprocessing wastewater and determining its potential nutrient value for growing crops. ' Contribution from the USDA-ARS Snake River Conserv. Res. Center, Kimberly, ID 83341, in cooperation with the Idaho Potato Commission and the .1. R. Simplot Co. Food Div., Caldwell, ID. Received 29 Apr. 1983. 'Soil Scientist and Biological Technician (Soils), retired, respectively, The objectives of this research were to compare potato-processing wastewater and NH 4N0,-N sources for corn (tea mays L.) production and thereby evaluate the wastewater as a N source. MATERIALS AND METHODS A field plot area was selected where both potato-processing wastewater and irrigation water were available. The wastewater was pumped to the plot area through a pipeline from a potato-processing plant nearby. An area 30.5 m wide by 183 m long containing 40 rows of corn of Moulton fine sandy loam soil (mixed mesic Typic Haplaquoil) near Caldwell, Idaho was irrigated with wastewater using a line source sprinkler in the center of the plot running the length of the plot. Sprinkler nozzles were spaced at 6-m intervals. Sixty rain gauges were installed in three rows of 20 across the plot in alternate corn rows to measure wastewater applications and the water was sampled during each irrigation to determine the N and chemical oxygen demand (COD) contents of the wastewaters. The total N content of the wastewater averaged 76 mg/L with < 2 mg/L NO,-N. Nitrogen in the wastewater applied to the plots ranged from 4 to 600 kg/ha (Table 1). Wastewater was applied five times in 1979 during the growing season and twice each year before planting corn in 1980 and 1981. During the first year the entire plot area was irrigated with wastewater; in the second year 122 m of length was irrigated and the 61 m remaining was left without wastewater irrigation for residual fertilization evaluation; in the third year 61 m of the plot was irrigated with wastewater, 61 m was evaluated for residual following 2 y of wastewater irrigation, and 61 m was evaluated for residual fertility value following . I y of irrigation with wastewater. Each 61 m plot area was divided into three areas of 20 m each for sampling. These served as replications for statistical analyses. An adjoining set of plots with the same soil and cropping history, 10 by 23 m each, was fertilized with NI-14NO, to provide 100, 200, or 300 kg N/ha annually. Each plot was split to fertilize one-third of the area with one, one-third with two, and one-third with three annual applications of fertilizer during the experiment for residual N evaluation. These plots were arranged in a randomized block design replicated three times. All of the experimental area was irrigated in the furrows between rows with Boise River water to meet the water requirements of the corn crop and to remove the water variable imposed by the wastewater irrigation. In 1979 the wastewater was applied in the early spring before planting and during the growing season to apply the desired amount of N. The following 2 y one irrigation was applied in the fall following harvest and another in the spring before planting. The excess water applied by wastewater irrigation in the center of the plots caused some extra leaching. Previous research (10) showed that the organic constituents of wastewater were removed from the water almost quantitatively in 60 cm of soil and would not leach. Therefore, the relatively uniform irrigations with river water were considered to eliminate the water variable for this experiment. The plots were treated with Atrex and Dual postemergence at recommended rates for weed control. Corn was grown on the plot areas for 3 y, harvested at maturity, and yields of corn grain and stalks were determined separately. At harvest, three 3-m row sections were cut by hand from each of 40 rows for each wastewater irrigation treatment, weighed, the ears removed, bagged, and weighed. The stalks were run through a forage chopper and sampled for moisture and chemical analysis. The stalk samples and ears were dried in an oven at 60°C, the corn shelled, and both corn and stalks were ground and analyzed for total N by a Kjeldahl procedure (1). The cobs were discarded. The corn rows were numbered from 1 to 20, starting at the center of the plot and going to the outside row, which was number 20, on each side of the plot. Corn varieties grown on the plots and adjacent area were `Greenway 55' in 1979 and 'Pioneer 3901' in 1980 and 1981. Plot preparation, planting, cultivation, irrigation, and harvest after plot samples were removed were performed by the cooperator. 3. Environ. Qual., Vol. 13, no. 1, 1984 151 Table I-Wastewater and N applied to plot area through a line source sprinkler.