Soil Properties affected by cover crops and fertilization in a crop rotation experiment

Summary

The aim of the current study was to investigate based on a five-year crop rotation experiment (field pea, potato, barley under-sown with red clover, red clover, and winter wheat) situated in Tartu, Estonia, the impact of cover crops (oilseed-rape, rye and perennial ryegrass), alone or with cattle manure (40 t ha-1), in organic farming and mineral fertilizers (up to N150P25K95) effect in conventional farming in soil chemical (pHKCl, SOC, Ntot, available P, K, Mg and Ca) and physical properties (bulk density, porosity, water permeability and penetration resistance) since 2008 till 2014. In addition in 2013–2014 the effect of cover crop on soil aggregate stability, earthworm population and microbial activity (FDA) was also tested in organic farming. After the first rotation, the organic systems counted with the highest C input as a result of the incorporation of the main crop residues, plus the ploughing of cover crops and the yearly addition of cattle manure, resulting a positive effect on SOC and N, increasing SOC by 1.47% since experiment started. However, the larger number of tillage operations carried out in these systems counterbalanced the positive effect of cover crops and manure on the soil physical properties in the organic systems which presented the highest bulk density (1.47 Mg m-3 and 1.48 Mg m-3, respectively) and the lowest percentage of air filled pores (14.6% and 14.1% respectively) compared with the conventional fertilized systems with lower bulk density (1.39 Mg m-3), higher percentage of air filled pores (19.1%) and plant available water (22.8%). During the second period, the sum of different factors such as intensive tillage and the decrease in Mg, affected the percentage of soil stable aggregates in the organic systems with cover crops and cattle manure, decreasing it by 1.6% and 9.5% respectively. Contrary, these systems presented higher number of earthworms and the highest enzymatic activity with FDA average values of 59.7 μg and 58.4 μg fluorescein g dry soil-1 h-1, respectively, compared to the control treatment. In summary, the use of cover crops alone or with cattle manure cannot be considered sufficient for maintaining a constant concentration of nutrients and good soil physical conditions in the soil after seven years of rotation under intensive tillage and further research is needed under lower tillage intensity.