Mj. Shipitalo et al., Conservation tillage and macropore factors that affect water movement and the fate of chemicals, SOIL TILL R, 53(3-4), 2000, pp. 167-183
A thorough understanding of how conservation tillage influences water quali
ty is predicated on knowledge of how tillage affects water movement. This p
aper summarizes the effects of conservation tillage on water movement and q
uality mainly based on long-term experiments on Luvisols at the North Appal
achian Experimental Watershed near Coshocton, OH, USA. Conservation tillage
can have a much larger effect on how water moves through the soil than it
does on the total amount percolating to groundwater. Soil macroporosity and
the proportion of rainfall moving through preferential flow paths often in
crease with the adoption of conservation tillage and can contribute to a re
duction in surface runoff. In some medium- and fine-textured soils most of
the water that moves to the subsoil during the growing season (May-October)
is probably transmitted by macropores. If a heavy, intense storm occurs sh
ortly after surface application of an agricultural chemical to soils with w
ell-developed macroporosity, the water transmitted to the subsoil by the ma
cropores may contain significant amounts of applied chemical, up to a few p
er cent, regardless of the affinity of the chemical for the soil. This amou
nt can be reduced by an order of magnitude or more with the passage of time
or if light rainstorms precede the first major leaching event. Because of
movement into the soil matrix and sorption, solutes normally strongly adsor
bed by the soil should only be subject to leaching in macropores in the fir
st few storms after application. Even under extreme conditions, it is unlik
ely that the amount of additional adsorbed solute transported to groundwate
r will exceed a few per cent of the application when conservation tillage i
s used instead of conventional tillage. In the case of non-adsorbed solutes
, such as nitrate, movement into the soil matrix will not preclude further
leaching. Therefore, when recharge occurs during the dormant season thoroug
h Bushing of the soil, whether macropores are present or not, can move the
remaining solutes to groundwater. Thus, the net effect of tillage treatment
on leaching of non-adsorbed solutes should be minimal. Published by Elsevi
er Science B.V.