Phytosociological survey of weeds in rice crops under drip irrigation with dairy effluent

The search for more sustainable systems of rice cultivation, especially in relation to water use, has included theevaluation of more-efficient irrigation systems in addition to alternative water sources. The aim of this study was to conducta phytosociological survey of weeds in rice crops irrigated by subsurface drip with different concentrations of treated dairyeffluent, maintaining the soil moisture at saturation or field capacity. A pilot scale experiment was carried out in a protectedenvironment using a randomised block design in a 5 x 2 factorial scheme, with four replications. The IAC 301 cultivar (Arborio rice)was chosen. The phytosociological surveys were carried out on four different dates, and considered the composition as wellas the distribution of plant species in each of the applied treatments, using the importance value index (IVI) to evaluate theinfluence of each treatment. The results showed that cultivating irrigated rice, giving priority to water management, alteredthe ecology of invasive plants. Fourteen weed species were identified, distributed over 10 families. The effluent dose didnot alter the incidence of invasive plants, and only at the final evaluation was there a reduction in the IVI value at effluentconcentrations of 50% and 75%. For soil moisture, the highest IVI values occurred on the first two days of the survey undersaturated conditions; this result was reversed closer to plant maturity, when the IVI values were higher at field capacity.