60
sugars,
50
cellulose
cover crop
40
(green)
proteins
30
hemicellulose
yield (bu/a) 20
polyphenols
lignin
compost
10
humus
0 0
2
4
6
8
10
available soil water (inches)
Figure 9.1. Relationship between winter wheat grain yield and soil water Figure 9.2. Different types of residues have varying effects on soils
at wheat planting over six years. Modified from Nielsen et al. (2002).
(thicker lines indicate more material, dashed lines indicate very small
percentage). Modified from Oshins and Drinkwater (1999).
Residue management in arid and semiarid
and soybean residue, decompose rapidly (figure 9.2)
regions. In arid and semiarid regions water is usually
and have a shorter-term effect on soil organic matter
the most common limitation to crop yields. For winter
levels than residues with high levels of these chemicals
wheat in semiarid regions, for example, the available
(for example, cornstalks and wheat straw). Manures,
water at planting often foretells final yields (figure
especially those that contain lots of bedding (high in
9.1). Thus, in order to provide more available water for
hemicellulose, polyphenols, and lignin), decompose
crops, we want to use practices that help store more
more slowly and tend to have more long-lasting effects
water in soils and keep it from evaporating directly to
on total soil organic matter than crop residues and
the atmosphere. Standing residue allows more snow
manures without bedding. Also, cows—because they
to be maintained in the field after being deposited,
eat a diet containing lots of forages that are not com-
significantly increasing available soil water in spring—
pletely decomposed during digestion—produce manure
sunflower stalks used in this way can increase soil water
with longer-lasting effects on soils than nonruminants,
by 4 to 5 inches. And a mulch during the growing season
such as chickens and hogs, that are fed exclusively a
helps both to store water from irrigation or rainfall and
high-grain and low-fiber diet. Composts contribute
to keep it from evaporating.
little active organic matter to soils but add a lot of well-
decomposed materials (figure 9.2).
Effects of Residue Characteristics on Soil
In general, residues containing a lot of cellulose
Decomposition rates and effects on aggregation.
and other easy-to-decompose materials will have a
Residues of various crops and manures have different
greater effect on soil aggregation than compost, which
properties and, therefore, have different effects on soil
has already undergone decomposition. Because aggre-
organic matter. Materials with low amounts of harder-
gates are formed from by-products of decomposition by
to-degrade hemicellulose, polyphenols, and lignin, such
soil organisms, organic additions like manures, cover
as cover crops (especially legumes) when still very green
crops, and straw will usually enhance aggregation more
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Building SoilS for Better CropS: SuStainaBle Soil ManageMent