Risk Assessment of Non-Uniformity in Irrigation and Fertilization for a Furrow Set Under Climate Uncertainties in the Sofia Field

Water distribution could be quite non-uniform along the furrow length under surface irrigation. This “down field” disuniformity is usually combined with “inter-row” nonuniformity of irrigation water and nitrogen fertilizer distribution. Spatial variation of application depth and nitrogen (N) fertilization rate in the furrow plot produces yield, drainage and nitrogen losses. In addition to that, due to year-to-year variability of climate, regional irrigation depths range significantly (from 0 to 360 mm/season in the studied field). The objective of this paper is to study the impact of global nonuniformity of irrigation water and N fertilizer distribution within a furrow plot on yield, water and nitrogen losses when climate variability is taken into account. Six maize vegetation seasons with contrastive probability of exceedence of irrigation depth PI are considered. Irrigation water is distributed according to six scenarios for “downfield” and “inter-row” non-uniformity by using the validated FURMOD model (Popova, 1990; 1992; Popova and Kuncheva, 1996). Nitrogen fertilization broadcast corresponds to two scenarios of lateral non-uniformity. The validated CERES-maize model (Jones and Kiniry, 1986;Gabrielle et al, 1995; Popova et al.1999; 2001- b; Popova and Kercheva, 2005) is applied with the different “climate-irrigation nonuniformity-fertilization nonuniformity” scenarios to simulate water&nitrogen cycle and crop growth on a daily basis in 30 representative points along “median”, “high intake” and ”low intake” furrows of the set. It is established that yield, water and nitrogen losses vary over uniformity scenarios and studied 30-year period. Combination of non-uniform irrigation/N-fertilization with the high irrigation demand seasons (having probability of exceedance PI<11%) causes losses of yield by 2 to 14.5 % of potential maize productivity, irrigation water (up to 40-45% of applied depth) and nitrogen (up to 10-12% of N-rate). Model runs show that poor distribution uniformity of irrigation water and N fertilizer should be maintained especially in the case of high irrigation requirements. Different strategies aiming at reduction of heterogeneity sources of “inter-row” and “down-field” uniformity of water distribution and fertilizer broadcast are recommended.