Land-forming for irrigation (LFI) on a lowland soil protects rice yields while improving irrigation distribution uniformity

During land leveling topsoil of relative higher elevation zones are removed (cut) and deposited in relative lower elevation zones (fill), this operation could have negative impacts on soil conservation and potentially can affect productivity. Although land leveling is an efficient way of increasing water use efficiency and irrigation uniformity, it can be rather expensive and, in some cases, a significant movement of earthwork may be required. Nowadays, with the technological advancement a new option is available called Landforming for irrigation (LFI). This alternative method potentially allows smaller soil movement and consequently smaller cutting depths while improving irrigation and drainage conditions without affecting productivity. The hypothesis of this study was that applying LFI can allow a more efficient irrigation than the commonly used procedure done by farmers (Control) without affecting productivity. For achieving this, a two-year 2018-2019 and 2019-2020 rice seasons comparison study was done in a semi-commercial field (12 ha) in Uruguay. This was the first time LFI was implemented in this country. For achieving the LFI alternative a soil movement of 104 m3 ha-1 was determined. The depth of cut was in average 0.03 meters, with a maximum cut of 0.16 meters. The total length and number of rice levees were reduced by 14% and 28%, respectively, compared to the adjacent Control field which was not graded. Irrigation water moved across the LFI field more quickly and uniformly as compared to the Control. For both years of the study, there were no differences (P>0.05) in field-average grain yields between the LFI and Control treatments even though yield increases and yield decreases were often associated with specific fill and cut zones, respectively. When data from both seasons are pooled together a significant relation was detected (% yield deviation = 0.81+140 * (cut depth (m)). Taken together, this work demonstrates that, by limiting the amount of soil moved as part of the land forming process, LFI can provide the level of rice productivity as traditional leveling practices common to South America while improving irrigation distribution uniformity, setting the stage for improved furrow irrigation of rotational crops such as soybean.