A two-year study was conducted in 2002-2003 (season one) and 2003- 2004 (season two) at a seepage irrigated vegetable farm in South Florida to investigate the effects of organic fertilizers on water movement in sandy soil. Season one results showed that for the same water table depth, soil moisture content in the compost field was higher than the noncompost field in the root zone (top 20 cm).
The increased soil moisture was attributed to the increased upflux due to increased capillary rise. Increased capillary rise was a result of increased organic matter content of the soil from compost application. After a rainfall event, soil moisture at 10 cm depth in the compost field responded rapidly, suggesting a higher extent of capillary fringe in the compost field compared to the noncompost field, which did not show the similar response. Another addition of compost further enhanced the soil moisture effect in season two.
Season two results showed a higher difference between compost and non-compost soil moisture from the previous season. Results from the study showed that the addition of compost can help in maintaining the same level of soil moisture with a lower water table compare to the noncompost field. A lower water table in the compost field can result in higher retention of rainfall in the soil compared to the noncompost field, which in turn can reduce runoff, deep percolation, and seepage losses and achieve water conservation.
Increased water retention is especially beneficial for areas with sandy soils. Agriculture practices on these soils require frequent irrigation inputs. Rapid water movement in recently fertilized sandy soils can potentially result in loss of nutrients through leaching. Eventually, leached nutrients reach shallow groundwater, from where it can laterally move to ditches and canals, adversely impacting the water quality of downstream water bodies. On the contrary, organic fertilizers improve rainfall retention in sandy soil and reduce irrigation input for vegetable production.