Abstract

Sapropel is a freshwater lake organic-mineral sediment complex, with estimated global reserves exceeding 100 billion tonnes. Sapropel can provide nutrients to soil-crop systems, including nitrogen, phosphorus, potassium, calcium, magnesium, manganese, zinc, boron, copper, iron, and biologically active organic matter. Laboratory and field investigations have demonstrated that sapropel treatments can significantly restore and improve the agrophysical, agrochemical, microbiological and biochemical properties of degraded and infertile soils for a period of up to 4-5 years and increase agricultural crop yields over that period. Thus, sapropel can be used in multifunctional agro-environmental technologies. However, despite the positive properties of sapropel, it is not used to its full potential. This is largely due to the high application rate of sapropel (typically 60t ha-1) needed to guarantee effectiveness and thus the associated high costs of processing and transporting the bulky material. Field experiments are in progress in Serapiniškės gravel/sand quarry in south-east Lithuania.

By applying precision agriculture Scarabaeus technology, non-productive soil is modified by targeting the local insertion of organic soil improver to specific underground inserts of sapropel ameliorant. The tractor-led agricultural machine (Scarabaeus) allows direct insertion of sapropel into the rooting zone (Rhizosphere). Thus, conditioners are only applied to the plant growth lines and directly into the root growth zone in 15cm diameter inserts of sapropel. The upper edge of the sapropel insert is usually set at 10-15cm depth beneath the plowed topsoil and the spacing between inserts is typically 55-75cm. This enables the soil improver to be added to specific localized underground inserts rather than onto the entire modified area, thus reducing the application rate five-fold. Fully replicated experiments were undertaken in 2019 and 2020 and further investigations are on-going. In the furrows with local application of the ameliorant at 11t ha-1 with the Scarabaeus machine, similar yields were obtained as in the furrows, where 60t ha-1 was applied in the traditional manner. Analysed soil physico-chemical properties included Soil Organic Matter (SOM), nutrient concentrations, the chlorophyll content of leaves, soil moisture, soil temperature and soil electrical conductivity. Direct soil treatment effects on soil biota were evident from the application of sapropel ameliorant. In soil samples taken from 0-10 and 10- 20cm in 2019, sapropel significantly increased soil respiration, the biomass of microorganisms, enzymatic activity, provided SOM, improved soil moisture retention, and decreased soil pH to levels suitable for crop production. Significant effects (P<0.001) were consistent in five sampled crops (fava beans, common beans, potatoes, and maize) and were particularly evident in the increased crop yield of leeks. Thus, the artificial soil produced using Scarabaeus technology was a suitable substrate for crop production. The evidence supports the premise that the technology has potential to improve agro-environmental conditions on sandy infertile soils in multiple climatic conditions, especially in arid areas, and thus merits further investigations.

Keywords: Sapropel; Lakes; Soil conditioners; Soil fertility; Precision agriculture; Rhizosphere; Arenosols; Aridisols; Pedogenesis