Nutrient Use Efficiencies
and Leaching of Organic and Conventional
Cropping Systems in Sweden
Gunnar Torstensson, Helena Aronsson, and
Organic farming has been proposed
as a means of reducing leaching and improving the
use efficiency of plant nutrients in agriculture.
In such systems, nutrient inputs originate from various
organic sources or from naturally occurring minerals
with low solubility. In this study, measurements of
leaching and crop uptake of N, P, and K and determinations
of mineral N in soil were conducted in tile-drained
plots during a 6-yr period in two organic crop rotations,
one with and one without addition of animal manures.
In the latter, N was provided by green manures. For
comparison, two conventional systems in which mineral
fertilizers and pesticides were used (one with cover
crops) were also included. Leaching loads of N were
smallest in the conventional system with cover crops,
on average 25 kg N ha-1 yr-1
over the 6-yr period. The corresponding amounts in
the other systems were 39 (organic with animal manure),
34 (organic without animal manure), and 38 (conventional)
kg N ha-1. Phosphorus-leaching loads were
small overall in all systems (<0.25 kg ha-1
yr-1). Potassium-leaching loads reached
on average 27 kg ha-1 yr-1 over
the 6 yr in the conventional systems and 16 kg ha-1
yr-1 in the organic systems. When N leaching
was expressed as a percentage of total N removal during
the 6-yr period (leaching plus harvested N with crops),
it represented 59% in the organic system without animal
manure, 33% in the conventional system, and 22% in
the conventional system with cover crops. These results
clearly suggest that N use efficiency is improved
if inorganic N fertilizers are used rather than green
manures, especially in combination with cover crops.
The superior system from all considerations was the
conventional system with a cover crop.
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