The Role of Intercropping in Plant Biofortification 5adjacent plant species. Iragavarapu and Randall ( 1996 ) grew maize with
soybean and wheat in a strip intercropping system and noted a 23% increase in
maize yield in the edge row adjacent to wheat and a 27% increase in the edge
row adjacent to soybean. The results of study conducted in south-east Poland
by Głowacka (2013b) also confirm the beneficial effect of strip cropping on
maize yield. The yield of maize in strip cropping was on average 11% higher
than in single-species cropping. This was the result of a considerable increase
in yield in the edge rows of the maize strip – by 26.0-29.6% in the row
adjacent to the common bean and by 17.0-21.5% in the row adjacent to spring
barley. It was also found that strip cropping significantly increased weight per
maize plant while decreasing plant height (by 23 cm) and increasing (by 4.2%)
percentage share of ears in the total yield. The increase in the percentage of
ears in the yield was particularly pronounced in the edge rows of the maize
strip (Głowacka 2014b). The greater amount of sunlight on the edge rows may
promote their overall biomass accumulation, while the greater height of the
inner rows apparently reflects the shade-induced stem extension later in the
season, since inner rows have lower biomass than edge rows (Jurik and Van,
1994; Lesoing and Francis 1999). The effectiveness of strip cropping is also
influenced by the arrangement of the strips. Yield is higher in edge rows on
the east side than in those on the west side. This is due to the faster
photosynthesis rate in the cool mornings when the sun reaches the eastern edge
of the strip in comparison with the hotter afternoons when the sun falls on the
western edge, and may not be fully utilized by maize plants due to water stress
and wilting (Jurik and Van 2004).
The efficiency of strip cropping also depends on weather conditions.
According to Garcia-Prechac ( 1992 ), strip cropping of maize, soybean and
oats is more efficient than sole cropping in years with average or high
humidity. Głowacka (2014b) found that the lowest yield with the lowest
percentage of ears was produced by maize in the year with the least
precipitation, which was also unevenly distributed. However, the increase in
maize yield in strip cropping in that season was 11.8% in relation to sole
cropping, which was the highest of all the years of the study. This may be
because barley and bean are less competitive in water uptake than maize.
Moreover, the significant rainfall shortages occurred in July, August and
September, when the plants accompanying the maize, particularly barley, have
lower demand for water. A plant frequently accompanying maize in strip
cropping is soybean. As a taller plant, maize can substantially restrict the
access of light to soybean and compete with it for water and minerals, in effect
reducing soybean seed yield (Egli and Yu 1991, Lesoing and Francis 1999).