Agriculture Reference
In-Depth Information
[18]. The value of the leftover position depends on the selection of components, their partici‐
pation in the stand, the level of yield and soil conditions. Studies have shown that the yields
of winter wheat cultivated after the mixture of pea with spring cereals (wheat, barley) were
higher from 5 to 27% than after spring barley, while after a mixture of yellow lupine with
triticale-by 31% compared to the yields following the triticale [19, 20]. Cereal species signifi‐
cantly affected the forecrop quality of the mixtures. Mixtures of legumes with wheat, barley
and triticale were definitely better forecrops for winter wheat than the same cereals cultivated
in sole crop, while a mixture with oats influenced on a small increase in the yield of successive
crops compared with sole oats [21, 22]. This is due to the characteristic of oats, which has
phytosanitary features and is considered as one of good forecrops for winter cereals. However,
cereal mixtures were a worse forecrop (Table 2). The share of components seeds in the mixture
also affects the catch crop value of the stand. A larger proportion of legumes in the mixture
positively affected the yield of the following plants (winter wheat). This reaction was higher
on good soils compared to the poorer ones [22, 23].
2.2. Biological nitrogen fixation
Biological process of atmospheric nitrogen fixation by the bacteria of
Rhizobium
and
Bradyrhi‐
zobium
that live in symbiosis with legumes has great significance for agriculture. In the
symbiosis process, legumes provide the bacteria with carbohydrates, and in return they receive
nitrogen assimilated by them, which they use to produce high-value protein. Nitrogen is used
by plants in almost 100%, while in the case of mineral fertilizers, the plants generally use not
more than 50% of this element. Cereals growing in the vicinity of legumes use the nitrogen
assimilated by nodule bacteria, as it is transferred to the soil in the form of aspartic acid or β-
alanine. This phenomenon is particularly important in low-input farming systems, especially
in organic agriculture, where the biological fixation is the most important source of nitrogen
[24, 25, 26].
The amount of nitrogen fixed by the nodule bacteria in the process of symbiosis depends
primarily on the species of legume as a component, its share in the mixture and the level of
nitrogen fertilization. The lysimetric studies with using
15
N have shown that in vetch sown
with oats, 90% of the total nitrogen uptake (about 53 kg ha-1) comes from symbiosis, while oat
uses about 28 kg of mineral N, which is one third of the nitrogen taken together by plants in
the mixture [27]. The studies under mixed sowings of maize with soybean and oat with vetch
have shown that exudates of active root nodules of legumes include NO
3-
ions, which affect the
increase of biomass and nitrogen content of non-legume components of these mixtures. The
permeation of nitrate ions took place at night-from late evening to early morning [28]. The
complementarity in the use of nitrogen by the mixture components was confirmed by a higher
uptake of nitrogen with the yield of mixture seeds of oat with pea compared to sole crops of
this species (Table 3). Almost twice as high nitrogen uptake with the yield of mixtures seeds
compared to seeds yield of barley was significantly associated with a large proportion of the
legume seeds in the sown mixture (70%). The research carried out in different European
countries (Denmark, Germany, Great Britain, France and Italy) has shown that the overall N
resources were used 30-40% more efficiently by pea-barley intercrops compared to the
