Agriculture Reference
In-Depth Information
8.5.1 u se of a dequate s eed r ate and r ow s paCInG
Adequate seed rate and row spacing are important factors in determining the number of plants per
unit area and consequently N uptake and use efficiency. Seeds used for sowing crops should have
a germination of more than 85% to get good plant stands. Row spacing is determined experimen-
tally for each crop under each agroclimatic condition. Adequate seed rate and row spacing do not
involve extra cost to the farmers but reflect significantly in yield determination. For example, in the
Brazilian Cerrado region or the central part of Brazil, the upland rice seed rate is about 80 kg ha −1
and row spacing about 30 cm. Similarly, the lowland rice seed rate is about 110 kg ha −1 and row
spacing varied from 18 to 20 cm. Dry bean is planted about 12-15 seeds per meter row and row
spacing is about 40 cm in the Cerrado region of Brazil.
8.5.2 u se of e ffICIent /t olerant C rop s peCIes and G enotYpes wIthIn s peCIes
It is estimated that a 1% increase in nitrogen use efficiency saves about 1.1 billion US$ annually
worldwide (Kant et al., 2010). Hence, to minimize the loss of N, reduce environmental pollution,
and decrease input cost, it is crucial to plant crop species or genotypes with higher nitrogen use
efficiency. Fageria and Baligar (2005) reported that planting crop species and genotypes within
species having a higher N uptake and use efficiency is an important strategy in modern agricul-
ture. Differences in N uptake and utilization among crop species and cultivars within species for
wheat, sorghum, corn, ryegrass, rice, and soybean have been reported (Moll and Kamprath, 1977;
Pollmer et al., 1979; Reed et al., 1980; Traore and Maranville, 1999; Fageria, 2014). Similarly, many
researchers have found significant variations of N use efficiency among lowland rice genotypes
(Broadbent et al., 1987; Singh et al., 1998; Fageria and Barbosa Filho, 2001; Fageria and Baligar,
2003b). Pandey et al. (2001) reported that agronomic efficiency of N was higher in sorghum com-
pared to pearl millet and corn over four N rates (45, 90, 235, and 180 kg N ha −1 ). Fowler (2003)
reported significant yield differences among wheat genotypes with increasing N rates from 0 to
240 kg ha −1 .
Plant species and genotypes within species differ in their ability for N uptake, utilization, and
conversion into economic entity under low input (Singh, 2013). Lemaire et al. (1996) observed that
N uptake by corn and sorghum were similar at high N input, but under N limitation, sorghum plants
acquired significantly more N than corn. A more developed and branched root system in sorghum
possibly permitted it to scrounge for N shortage (Hirel et  al., 2007). The existence of genotypic
variation for nitrogen use efficiency has been recognized for a long time (Smith, 1934; Springfield
and Salter, 1934). Svecnjak and Rengel (2005) reported differences among spring canola genotypes
in nitrogen use efficiency, which resulted in greater biomass with parallel performance at high and
low N inputs.
Isfan (1993) reported highly significant variation among oat genotypes in both yield and physi-
ological efficiency of absorbed N. According to this author, ideal genotypes could be those that
absorb relatively high amounts of N from the soil and fertilizers, produce high grain yields per unit
of absorbed N, and store relatively little N in the straw. Similarly, many workers found corn genotype
differences for the absorption and utilization of N (Kamprath et al., 1982; Moll et al., 1982, 1987;
Anderson et al., 1984). Lynch and White (1992) and Lynch and Rodriguez (1994) reported genetic
variability in N use efficiency of dry bean genotypes. Experiments with the U.S. corn belt (Balko
and Russell, 1980), tropical (Muruli and Paulsen, 1981; Lafitte and Edmeades, 1994; Banziger et al.,
1997), and European maize (Bertin and Gallais, 2000; Presterl et al., 2003) indicated that genotypes
can differ considerably in their N use efficiency. Hence, breeding for adaptation to low soil N seems
feasible.
A direct relationship between the N fertilizer rate and corn plant growth and grain yields has
been widely demonstrated (Jokela and Randall 1989; Zhang et al., 1993; McCullough et al., 1994;
Costa et al., 2002). However, studies with conventional corn hybrids (Chevalier and Schrader, 1997)
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