Is it drainage or water management? – South East Farmer – Dick Neale
Dick Neale, Hutchinsons’ soil expert and technical manager, shares his point of view ...
Drainage is generally considered to be the process of emptying a place or mass of liquid. In the relationship with soil, drainage is about controlling any excess water beyond that which the soil can naturally hold or store.
It is key to understand the component of water storage in soil. Just being focused on moving water through and out of soil as quickly as possible during wet winter periods ignores the needs of crops later in the year, when they will be reliant on the soil’s ability to store and then release that water.
Without a focus on storing water during the winter, there will be no water to sustain growth in the summer.
There is an increasing realisation that our soils are becoming degraded. This occurs most rapidly and severely at the soil surface, where we focus cultivations and where the weather has most direct impact.
The past two seasons have seen severe ponding of water at the soil surface following periods of heavy rain. Some of these ponds disappear in two or three days, while others persist for weeks.
Where ponding occurs, the first area to inspect is the soil’s ability to allow water to infiltrate the soil surface. This is not drainage in the accepted sense; the drainage out of the soil may be working fine, but without the ability of the water to infiltrate the soil surface, it can never reach the drains and, equally, it cannot be stored for future use.
Water management is about controlling the infiltration, flow, storage and release to plants of that water, which is fundamentally different to the focus of getting water out of soil as fast as it falls.
Maintaining drainage via the jetting of pipes, cleaning of ditches and installation of moles is of course vital in high clay level soils where naturally impervious layers of clay exist, but the need for water to infiltrate the soil surface must be an area of focus; it’s where things are going wrong.
Surface stability and ability to allow water entry is down to soil aggregate stability. Aggregates are built and stabilised via natural processes, organic matter, roots, microbiology and worms. There is no machine you can buy to sort this – in fact cultivation implements are the single most disruptive tools in aggregate destruction.
That does not mean there is no place for an appropriate cultivation, but it must be utilised in conjunction with natural soil surface protection and stabilisation.
These only come from biological processes; cover crops shielding the soil from direct rain impact and roots stabilising the moved soil and managing water, worms moving soil and creating bio pores for water movement to depth and the aggregates themselves, providing resilience to weathering and the pore space for long term water storage.
Cover crops are not practical in every situation, and species make-up of that cover is vitally important within the water management cycle.
However, volunteer growth or crop residue can be employed successfully to reduce soil surface degradation and capping; there is a good reason why stubble fields often remain pond free and walk clean after heavy rain whereas the cultivated seedbed next door is ponding and you sink to your ankles.
This is because we have destructured the soil and disrupted water flow through excessive or unstable cultivation, whereas the soil below the stubble remains in a naturally structured state with the surface protected via the standing stubble. It’s important that we learn from what we observe.