Agriculture Reference
In-Depth Information
more fixed N to the soil if sown immediately after a cereal crop than if grown in previously fallowed
soil or immediately after a legume-based pasture.
7.7.2.3 Planting High N
2
-Fixing Crop Species or Genotypes within Species
Planting high N
2
-ixing crop species or genotypes within species is an important strategy in
improving biological N fixation by legumes. There are evidences in the literature that the choice
of species or cultivar significantly influences N
2
fixation in cropping systems (Wani et al., 1995;
Peoples et al., 1995b). For example, in the Brazilian Cerrado region (central part), soybean in rota-
tion with upland rice and corn can fix a significant amount of N that is not only sufficient for a good
yield of soybean but that can also contribute to succeeding cereal crops. However, for planting dry
bean in rotation with upland rice and corn, chemical N is required even for a maximum economic
yield of dry bean because dry bean is considered as a poor N-fixing legume (Herridge and Danso,
1995).
Peoples et al. (1995a) reported that examples of variation in the genetic capacity of different
species to grow and fix N under the same environmental conditions are presented for crop and
pasture legumes, tree legumes, and green manures. In a comparison of upland food legumes in
Thailand, for instance, black gram, green gram, and soybean all had similar growth patterns
(64-73 days to maturity), but black gram appeared to be better adapted to the environment and
fixed more N than the other species (Peoples et al. 1995b). However, in a related investigation in
Australia, soybean had a much longer duration of growth than black gram (140 days vs. 95 days,
respectively), and consequently had a greater growth potential and opportunity for N
2
fixation
(Peoples et al., 1995b).
7.7.2.4 Pest and Disease Control
Pests and diseases influence legume crop growth, including leaf area and root growth, which influ-
ence the N
2
fixation capacity. Crop and pasture losses from 10% to >90% resulting from diseases
have been reported (Johnston and Barbetti, 1987; Peoples et al., 1995a). Diseases or insects can be
controlled by adopting appropriate crop rotation, by applying fungicides or insecticides at adequate
rates and at the appropriate time, and by planting disease or insect-resistant crop species or geno-
types and high-quality seeds (Peoples et al., 1995a).
7.7.2.5 Plant Nutrition and Soil Amelioration
Supply of adequate amounts and proportions enhances the growth and development of legume
crops and, consequently, higher capacity of dinitrogen fixation. The root growth of most legumes
has been significantly increased with the addition of essential macro- and micronutrients (Fageria
and Moeira, 2011; Fageria, 2013). Similarly, the root growth of legumes such as dry bean, soy-
bean, and tropical legume cover crops has been reported to improve with the addition of essential
nutrients in low-fertility soils (Fageia, 2013). The root growth of most legumes improved with the
addition of lime and gypsum in acid soils of the cerrado region of Brazil (Fageria and Moreira,
2011). Peoples et al. (1995) reported that applying starter N fertilizers to legumes may depress
the N
2
fixation.
7.7.2.6 Plant Breeding and Selection
Enhancing crop legume dinitrogen fixation through plant breeding and selection is an important
strategy. The potential for enhancing N
2
fixation through breeding and selection was recognized
long ago (Phillips et al., 1971). However, progress has been slow (Herridge and Danso, 1995).
Mytton (1983) and Graham and Temple (1984) noted that little attention had been given to enhanc-
ing N
2
fixation through breeding, and basic information necessary for understanding the expression
of desired characters was largely absent. Herridge and Danso (1995) cited two main reasons for this
apparent lack of success. First, it is a difficult task to combine a single, desirable trait such as N
2
fixa-
tion with other agronomic and yield traits. Second, still techniques for the accurate determination
