Changes in water retention properties due to the application of sugar foam in red soils

This work describes the influence of the application of sugar foam (an organic residue from sugar beet industry) on water retention properties, over an extended period of time (>25 years), in two red soils in the La Mancha region of Spain. The properties of gravimetric moisture at field capacity, gravimetric moisture in the permanent wilting point and available water retention capacity both in the original soil – without the addition of sugar foam – and in the soil affected by the addition of sugar foam are compared. For this purpose, the profiles are characterised macro morphologically. Chemical, physical–chemical and mineralogical parameters are determined, in addition to determining the water retention curves of each soil with tensiometers and Richards pressure plates. The sugar foam applied to the soil altered its physical and chemical properties. An increase in contents of organic matter (3.5% versus 1.4%), calcium carbonate (40.8% versus 0%) and pH (8.2 versus 6.3) are observed in the superficial horizon of the studied soils, although there is no such significant increase in electrical conductivity (0.33 dS/m versus 0.25 dS/m). With regard to the physical properties, the depth of horizon A increases (32 cm versus 12 cm), the stoniness reduces (5% versus 25%), the structure is well developed, due to the texture becomes finer (silty versus sandy clay loam), and, finally, the bulk density reduces (0.79 g cm−3 versus 1.19 g cm−3). The gravimetric moisture at field capacity was 49% in the soil altered with sugar foam, versus 12% in the non-altered soil; the gravimetric moisture in the permanent wilting point was 14.5% versus 8% and the available water retention capacity was 34.5% and 4%, respectively. It can be concluded that the increase of calcium carbonate, organic matter and the reduction of bulk density are the most influential factors in this process. The scientific novelty of this work is that the hydro-behaviour of the soil due to the addition of sugar foam improves the characteristic values of moisture and, therefore, the agronomical qualities of the soil.