Deeper Rooting: Can topsoil management improve subsoil rooting?

Encouragement of deep burrowing earthworms might enhance yields by enabling deeper rooting, and capture of more sub-soil water.

Limited rooting depth is suspected to be a major limitation to current yields as cereal and OSR roots are not able to penetrate through strong soils. The Deeper Rooting FIG tested whether reduced soil cultivation and/or the addition of farmyard manure (FYM) would increase earthworm populations and so improve the rooting depth and subsequent yield of cereal crops. Deep burrowing (anecic) earthworms can improve soil structure by creating deep vertical burrows which provide soil aeration, drainage and channels for roots to explore. However, anecic earthworms are often absent from conventionally managed agricultural land due to frequent soil disturbance and lack of leaf litter at the soil surface.

Members of the Deeper Rooting FIG at a field site.

This study used tramline trials in six fields across four farms to test whether a combination of reduced cultivations or direct drilling plus the addition of cattle FYM, could boost earthworm populations and subsequently improve crop rooting and yield.

The study found significantly improved yields with FYM additions at one of the four study sites; however this may have arisen from improved nutrition. There was a trend for higher earthworm numbers and midden counts (accumulations of leaf litter above the burrow of an anecic earthworm) in treatments where FYM had been added and cultivation methods were less disruptive, although these effects varied between fields. The effect of soil cultivation treatments and manure additions upon earthworm populations are expected to be clearer in the second year of this trial when the earthworm populations have had a longer period to recover.

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