DISTRIBUTION OF SOIL MOISTURE IN THE PROFILE OF TYPICAL CHERNOZEMS UNDER WIDE-SPACE IRRIGATION AND IMPACT ON THE YIELD OF MAIZE (Zea mays L.)

Irrigation in Bulgaria is a common agricultural practice for improving and stabilizing crop yields. Recently, the socioeconomic conditions and climate peculiarities set the pattern for practicing water saving irrigation technologies. Irrigation in ever-other-furrow on capillary soils is a way to save water amounts, to improve water use efficiency and to protect soil structure. The goal of the paper is to present the seasonal water depletion in soil profile of chernozems under maize at different intra-furrow spaces and different application depths. The relation of yield to soil moisture unevenness and water deficit is discussed. A two-year experiment in 2009 and 2010 was conducted in Central North Bulgaria, in the experimental field of Maize Research Institute Knezha. The following variants were tested: rainfed (RF) (control), full irrigation at a refill point (RP) 80% of field capacity (FC), 50% deficit irrigation (DI), and 67% DI. The water was distributed as follows: in every furrow (EF), in every-other furrow (EOF) and in ever-third furrow (ETF). Considering the rainfall totals, both years were medium wet, while considering air humidity they were very dry. The yields under rain-fed conditions were high -average 7.01 Mg/ha, while the yields under full irrigation comparatively low-9.39 Mg/ha. The additional yield under full irrigation in both years was 1.98 and 2.79 Mg/ha respectively, under 50% DI -8.54 and 8.75 Mg/ha, and under 67% DI-8.09 and 8.24 Mg/ha. Yield losses caused by DI relate nonlinearly to the application depth reduction. A 50% reduction of the application depth caused 5.8-6.8% yield losses in 2009 and 8.0-17.7% in 2010. A 67% reduction of the application depth caused 7.0-9.8% yield losses in 2009 and 17.3-18.1% in 2010. Greatest yield losses occurred at 67% DI in ETF, but the smallest ones -at 50% DI in EOF. EOF irrigation technology proved to be water-accumulating. The lower layers of chernozems tended to accumulate available water through all the vegetation season long in a continuous zone. Therefore the space between furrowsdidn't impact significantly the yield even under deficit irrigation.