GPS AND GIS BASED N-MAPPING OF AGRICULTURAL FIELDS’ SPATIAL VARIABILITY AS A TOOL FOR NON-POLLUTING FERTILIZATION BY DRIP IRRIGATION

Abstract

A study on nitrates’ spatial variability using GPS and GIS processing and mapping, and the effects of drip irrigation interval and applied nitrogen fertilizer, in the movement, concentration and depletion of total N, NO3-N and NH4-N in the soil and concretely in the active rhizosphere of maize cultivation showed serious infield variability in an experimental field at the Technological Educational Institute of Larissa, Thessaly Valley, Central Greece, in the farming period of the year 2001. Experimental variables were three irrigation frequencies and four nitrogen applications. For crop, corn was selected because it has high nitrogen requirement, which increases the potential for nitrate leaching. Three treatments (i.e. irrigation per 2, 5 and 9 days) were applied in a four replication, randomized complete block design with systematic plot arrangement. The randomization has been done with the method of statistical tables. The N source was an NPK fertilizer at the beginning of cultivation period (first dosage) at a rate of 89.6 kg N/ha (or 31.48% of the applied total nitrogen) as basic fertilization and urea (46% N) applied three times (second, third and fourth dosage) with a hydro-fertilization system (fertigation) in irrigation water, at a rate of 65 kg N/ha (or 22.84% of the applied total nitrogen) through the drip irrigation system at the root zone. Spatial evaluation, analysis and classification at field (treatments) level derived nitrogen management zones. Results showed that nitrogenous fertilizers and irrigation water require careful management in order to minimize the dangers of NO3-N leaching under the root zone in irrigated cultivations of maize. The present study correlates irrigation frequency and soil nitrogen depletion with nitrate concentration GIS maps showing nitrates’ spatial variability and also attempts to formulate a more precise and environmental friendly management scheme with variable rate technology farm machinery and precision agriculture.