Agriculture Reference
In-Depth Information
practice is increasing in recent years because of the high cost of chemical fertilizers, increased
risk of environmental pollution, and need of sustainable cropping systems (Fageria, 2007). Cover
crop/green manuring can improve the soil physical, chemical, and biological properties and, con-
sequently, the crop yields. Cover crops or green manuring can increase cropping system sustain-
ability by reducing soil erosion (MacRae and Mehuys, 1985; Smith et al., 1987), by increasing
SOM and fertility levels (Cavigelli and Thien, 2003), and by reducing the global warming potential
(Robertson et al., 2000). Cavigelli and Thien (2003) reported that incorporating green manure crops
into the soil may increase P bioavailability for succeeding crops. Furthermore, the potential benefits
of cover crop/green manuring are reduced NO
−
leaching risk and lower fertilizer N requirements
for succeeding crops (Fageria et al., 2005). However, its influence may vary from soil to soil, crop
to crop, environmental variables, and the type of green manure crop used and its management. The
beneficial effects of cover crop/green manuring in crop production should not be evaluated in iso-
lation, however, in integration with chemical fertilizers (Fageria et al., 2005; Baligar and Fageria,
2007; Fageria, 2007) (Table 4.7).
Soil compaction is a major problem for crop production around the world. Deep-rooted cover
crops are one possible solution to compaction problems, especially in no-till farming systems
(Unger and Kaspar, 1994; Williams and Weil, 2004). The deep-growing tap roots of the perennial
alfalfa (
Medicago sativa
L.) can increase the infiltration rate on compacted no-till soils (Meek et al.,
1990), and the recolonization of root channels left by alfalfa has been shown to benefit the corn (
Zea
mays
L.) root systems that follow (Rasse and Smucker, 1998). Similarly, Williams and Weil (2004)
reported that soybean (
Glycine max.
L. Merr.) roots were observed to take advantage of the root
channels left by the decomposition of cover crop roots of cereal rye (
Secale cereale
L.) and forage
radish (
Raphanus sativus
L. Diachon).
TABLE 4.7
Response of Upland Rice and Common Bean to Chemical Fertilization and Green
Manuring Grown in Rotation on a Brazilian Oxisol
Second
Upland
Rice Crop
b
Third
Upland
Rice Crop
First Upland
Rice Crop
b
First Bean
Crop
Second
Bean Crop
Third Bean
Crop
Fertility Level
a
Grain Yield (kg ha
−
1
)
Low
2188a
1935b
2383a
866c
480c
890c
Medium
2428a
2382a
2795a
1831ab
1127b
1242ab
High
2330a
2568a
2657a
2432a
1324b
1486a
—
2344a
—
1202bc
2403a
1065bc
Medium + green manure
Source:
Adapted from Fageria, N. K. and N. P. Souza. 1995.
Pesq. Agropec. Bras.
30:359-368. With permission.
Note:
Values followed by the same letter in the same column are statistically not different by Tukey's test at the 5% prob-
ability level.
a
Soil fertility levels for rice were low (without addition of fertilizers); medium (50 kg N ha
−1
, 26 kg P ha
−1
, 33 kg K ha
−1
,
and 30 kg ha
−1
fritted glass material as a source of micronutrients); and high (all the nutrients were applied at double the
medium level).
Cajanus cajan
L. was used as a green manure at the rate of 25.6 t ha
−1
green matter. For the common bean,
the fertility levels were low (without addition of fertilizers); medium (35 kg N ha
−1
, 44 kg P ha
−1
, 42 kg K ha
−1
, and 30 kg
ha
−1
fritted glass material as a source of micronutrients); and high (all the nutrients were applied at double the medium
level).
b
The first and third rice crop plots with a medium + green manure fertility level were planted with green manure and incor-
porated about 90 days after sowing (at flowering) and hence the grain yield was not presented.
