Agriculture Reference
In-Depth Information
Therefore down-leaching of water enriched with nitrate to the deeper parts
of the vadose zone is unavoidable. On the other hand, accurate fertigation
methods that synchronize the fertilizer's implementation with the nutrient
uptake capacity of the plants, as is commonly practiced in conventional
agriculture, dramatically reduce the amount of nitrate leaching through the
vadose zone to the groundwater.
14.4 SUMMARY AND CONCLUSIONS
Comparison of the groundwater pollution potential of greenhouses that
grow year round vegetables under intensive regimes shows that commer-
cial farms that rely on compost as the main fertilizer source, as commonly
practiced in organic agriculture, result in substantial down-leaching of ni-
trate compared with farms that rely on fertigation methods, as commonly
practiced in conventional agriculture.
The study implemented vadose zone monitoring technology that al-
lowed frequent sampling of the sediment pore water at multiple points
across the entire vadose cross section from the root zone to the water table
over a long time period. Nitrate concentration profi les under the farms
that rely on solid fertilizers revealed an increased concentration pattern
with a depth to average of 724 mg L
−1
. On the other hand, concentration
profi les in farms that rely on implementation of liquid fertilizers through
the irrigation systems during the growing season exhibited a reducing
concentration with a depth to average concentration of only 37.5 mg L
−1
,
immediately under the root zone. Isotopic composition ∂
15
N and ∂
18
O in
nitrate from the vadose zone under the sites confi rmed that the high nitrate
concentration under the studied organic farms is likely to have originated
from composted manure, while the nitrate under the studied conventional
greenhouse, though in low concentrations, is likely to be from industrial
or natural soil sources.
All studied greenhouses, organic and conventional, were established at
the same time, grow similar vegetables, use similar amounts of water and
total N-fertilizers, and share most agro-technical practices. Nevertheless,
the main difference between the greenhouses is related to the fertilization
regime. While organic agriculture in greenhouses relies mostly on solid
