Organic Agriculture Effect On Water Use, Tile Flow, And Crop Yield

Long-term crop rotations in organic agricultural systems provide N additions through legumes and residual organic materials to improve soil properties. In addition, enhanced pest management and more efficient water use in the spring and fall may result from the plant biodiversity in organic rotations. The purpose of this study was to compare organic and conventional systems in terms of tile flow or water use, and to determine if corn (Zea mays L.) or soybean [Glycine max (L.) Merr.] yields differed between systems. The experimental plots were in central Iowa and consisted of three treatments: 2-yr conventional rotation (both crops each year in split plot), 4-yr organic rotation (all crops present each year), and organic grass-legume forage. In the fall of 2017, 2018, and 2019, organic forage used more water than the mean of the 4-yr organic rotation, which used more water than the 2-yr conventional rotation. The same trend was shown for the spring of 2017 and 2019. Conventional corn had higher yield than organic for 3 of 8 yr, with 5 yr not significant. Conventional soybean had higher yield than organic for 2 of 8 yr and lower for 1 yr, with 5 yr not significant. Grass weeds were inversely correlated with leaf area index of corn on 3 of 10 measurement dates and for soybean on 5 of 10 measurement dates, but broadleaf weeds only on one date for soybean. Organic agricultural systems had positive benefits for timing of water use in the spring or fall by forage, alfalfa (Medicago sativa L.), or oat (Avena sativa L.). Some years had comparable yields to conventional corn and soybean.