|Image from California Agriculture|
Since 2004, University of California scientists have been studying “conservation tillage,” a suite of techniques that includes practices such as reducing tillage and leaving crop residues in the field after harvest. Leaving crop residues, in permacultural lingo, “chop and drop,” it turns out has a number of important benefits.
In two field studies comparing no-tillage with standard tillage operations (following wheat silage harvest and before corn seeding), we estimated that 0.89 and 0.97 inches more water was retained in the no-tillage soil than in the tilled soil. In three field studies on residue coverage, we recorded that about 0.56, 0.58 and 0.42 inches more water was retained in residue-covered soil than in bare soil following 6 to 7 days of overhead sprinkler irrigation. Assuming a seasonal crop evapotranspiration demand of 30 inches, coupling no-tillage with practices preserving high residues could reduce summer soil evaporative losses by about 4 inches (13%).
While this study is about commercial agriculture, much of its findings apply to home gardens as well, in my opinion. Leaving residues from the previous crop as a mulch layer saves water and builds soil. It does, of course, make it harder to direct sow seeds, but this is one of the reasons I like to work with transplants.
So don’t keep that vegetable garden too neat!