BPM: Use crop rotation and cover crops to minimize
nutrient loss
Compared with other annual crops
(cereals, oil sees, etc.) vegetable crops inherently have higher nutrient
pollution potential. In addition to being more heavily fertilized, many
vegetables are shallowly rooted (which limits N uptake at soil depths
> 30-45 cm) and have a high N content in residue (which rapidly mineralizes
upon soil incorporation). Even with appropriate fertilization and irrigation
practices, following vegetable production significant quantities of
mineral N may remain in the soil profile, at risk of loss to the environment.
Crop rotation, and the use of cover crops during fallow periods, can
minimize loss.
Rotating a shallowly rooted vegetable crop [lettuce, onion, potato (Solanum
tuberosum), etc.] with a more deeply rooted crop allows for recovery
of NO3-N from lower soil depths. Crops such as sugar beet (Beta vulgaris),
corn, and some cereals may extract N below 1.5-m depth. Where vegetable
cropping would normally be followed by an extended fallow period, production
of a cover crop can provide the same benefit. Others found that non-legume
cover crops such as phacelia (Phacelia tanacetifolia) and annual rye
(Secale cereale) planted after a broccoli crop reduced winter NO3-N
leaching by >60%.
Beyond soil NO3-N recovery, cover cropping can dramatically reduce field
runoff and associated sediment loss. It has been reported that cover
cropping following tomato production reduced winter runoff volume by
up to 70%. Erosion control with cover crops has been well documented.
Erosion control can be particularly important in fields with high STP,
since sediment-bound P represents the vast majority of total P in runoff.
There are both economic and cultural constraints to the use of crop
rotation and cover cropping. Growing a deeply rooted rotational crop
may have substantially lower profit potential than producing another
shallowly rooted vegetable. Cover crop production may involve significant
costs, complicated tillage practices, and disrupt spring planting schedules.
However, adoption of these practices may be indispensable in some vegetable
cropping systems to reduce nutrient losses.
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