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Impact of Variable Rate Fertilization on Ground Water Contamination in Wild Blueberry Cropping System

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2011 Louisville, Kentucky, August 7-10, 2011  1110631.(doi:10.13031/2013.37256)
Authors:   Shoaib Rashid Saleem, Qamar Uz Zaman, Arnold W Schumann, Ali Madani, David C Percival, Aitazaz A Farooque, Fahad S Khan, Scott Read
Keywords:   Precision agriculture, management zones, prescription map, nutrients leaching, leaf nutrients, lysimeter

Wild blueberry fields have gentle to severe topography with high proportion of bare spots, and weed patches. A wild blueberry field has been selected for variable rate (VR) fertilization based on variation in topographic features to improve farm profitability and fertilizer use efficiency, and reduce ground water contamination. Management zones (zone 1 through 3) were delineated and GPS-guided prescription map was generated in Arc GIS 9.3 based on variations in slope and bare spots in the field. Three fertilization rates (200, 150, and 100 kg ha-1) were applied with a VR fertilizer spreader according to the prescription map. Zero rates were allocated to the bare spots in prescription map. For comparison, half of the field received the growers uniform fertilizer rate of 200 kg ha-1. Soil leachate samples were collected after every heavy rainfall from suction lysimeters installed at 40cm depth below soil surface from 36 points in each 18 paired plots. The leachate samples collected were analyzed for nitrate nitrogen (NO3--N), and ammonium nitrogen (NH4+-N) concentrations, and leaf samples were analyzed for leaf nutrient concentrations under VR and uniform fertilization. The VR treatment significantly (p=0.05) decreased NO3--N and NH4+-N loading from leachates leaving the root zone in moderate and low lying areas when compared to the uniform treatment. Mean leachate NO3--N concentrations for all VR treatments ranged from 2.71 to 3.84 mg L-1, while those under uniformly fertilized in moderate slope and low lying areas were 7.72 and 8.52 mg L-1 respectively. Although, phosphorus, nitrogen and potassium in leaf nutrients were more than recommended ranges in zone-2 and zone-3 of uniformly fertilized section but most of other nutrients were within the optimal ranges. VR treatment used 42% less fertilizer than standard uniform fertilization and could protect environment.

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