Agriculture Reference
In-Depth Information
In the High Plains of Texas, the issue of water conservation is serious and a study
was conducted to compare cotton (
Gossypium hirsutum
L.) grown continuously
with cotton integrated with pasture (Allen et al. 2008). Cotton lint yield was simi-
lar (1.4 Mg ha
−1
) between continuous cotton and cotton rotated with grazed wheat,
rye (
Secale cereale
L.), and Old World bluestem (
Bothriochloa bladhii
[Retz] S.T.
Blake) (Allen et al. 2012). Additional bluestem seed yield and cattle weight gain
were achieved in the integrated system. On a farm basis, the integrated system used
25% less irrigation water, required 36% less nitrogen fertilizer, and had fewer other
chemical inputs than continuous cotton.
In a 9-year study of integrated crop-livestock systems in North Dakota, an aggre-
gated soil quality index did not differ between integrated annual cropping and peren-
nial grass (Liebig et al. 2012). With careful management, agricultural producers can
convert perennial grass pastures to winter-grazed annual cropping systems without
adversely affecting near-surface soil quality. Results may have been region specific
owing to consistent freeze-thaw and wet-dry cycles typical of the northern Great
Plains, use of no-till management, modest fertilizer application rates, and winter
grazing that avoided deterioration of soil with exploitation with cattle.
Ryan et al. (2012) made a compelling case for annual vetch (
Vicia
L. [Fabaceae]) for
hay or grazing paired with barley (
Hordeum vulgare
) in rotations for the Mediterranean
region, suggesting that barley-vetch rotations could potentially enhance barley yields,
improve soil quality, and provide valuable fodder for small ruminants. Medic (
Medicago
L. [Fabaceae]) and vetch in barley rotations increased SOC compared with traditional
cereal cropping (Ryan et al. 2009). In a 14-year trial that examined numerous legumes
in cereal rotations, legumes in rotation and nitrogen fertilization increased SOC levels;
however, grazing the cereal stubble reduced SOC (Ryan et al. 2008).
Chan et al. (2011) found that pasture holds the key to maintaining or increasing SOC
under long-term crop-pasture studies in New South Wales, Australia. Under pasture
converted to continuous cropping, the high initial SOC stock was, at best, maintained
with multiple conservation practices but tended to decrease with increased tillage or
stubble burning practices. Increases in SOC were observed only in rotations incorpo-
rating a pasture phase, with results suggesting that improved soil nutrient and grazing
management of permanent pasture can lead to an increase of 0.5-0.7 Mg ha
−1
year
−1
where the initial SOC concentrations were below steady-state levels.
Carvalho et al. (2010b) recommended crop-livestock systems as an alternative
to unsustainable intensive farming systems to address loss of biodiversity, nutrient
pollution, and habitat fragmentation, and illustrated these benefits by focusing on
the use of grazing animals integrated with crops under no-till systems characteristic
of southern Brazil. With increasing pressure for more cropland in southern Brazil,
da Costa et al. (2009) showed that converting from native grassland to an integrated
crop-livestock system under no till preserved soil physical conditions better than
under conventional tillage, while reduced tillage had a moderate performance. Crop-
pasture rotations have been the predominant cropping system in Uruguay since the
1960s (García-Préchac et al. 2004) and compared with continuous cropping with
conventional tillage, crop-pasture rotations provide less variable interannual eco-
nomic results, and soil degradation during the crop phase could be addressed by
combining crop-pasture rotations with no tillage management.
