Agriculture Reference
In-Depth Information
can be obtained under favorable environmental conditions (solar radiation, water, fertility, control
of diseases, insects, and weeds) using modern cultivars. Fischer et al. (2009) reviewed the literature
and reported that potential yield increase can be significant if C
4
pathways of photosynthesis could
be incorporated into rice. To obtain a yield of about 18 Mg ha
−1
, there will be a need of more than
300 kg N ha
−1
. Such a high amount of N should be applied fractionally during the rice growth cycle
and the timing should be determined in field experiments under each agroecological condition.
1.2.7.2.3 Corn
Corn has C
4
photosynthetic pathway and the potential yield may be higher as compared to wheat
and rice, which have C
3
photosynthetic pathways. Fischer et al. (2009) reported that the maximum
yield recorded for corn was from Chile (>20 Mg ha
−1
). The Chile central valley climate is more
favorable than the U.S. corn belt. The grain yield of 20.9 Mg ha
−1
was recorded for corn grown
near Manchester, Iowa, which was obtained from a harvest area of 0.5 ha that was within 2 ha field
(Murrell and Childs, 2000). However, Cassman et al. (2003) reported that, in Nebraska, the corn
yield of 21-23 Mg ha
−1
has been reported in contests but the Nebraska number is an average for the
period 1983 to 2002.
In addition, an estimate of the theoretical yield potential of about 25 Mg ha
−1
has been reported
for corn grown under conditions encountered in central North America (Tollenaar, 1983). This
estimate was based on the mean daily incident solar irradiance during the growing season and a
number of assumptions (Tollenaar and Lee, 2002): (i) leaf photosynthetic efficiency is 0.067 mol
CO
2
per mole photon or a 4.4% efficiency of conversion of intercepted photosynthetic active radia-
tion into crop biomass, (ii) full light interception between 1 July and 30 September and some
simplifying assumptions about light interception before and after this period, (iii) 50% GHI, and
(iv) roots constitute 10% of total crop dry matter at physiological maturity. This estimate is simi-
lar to several high yields obtained by corn producers (Tollenaar and Lee, 2002). Such high levels
of corn yield will require a very high amount of N to attain and sustain production. Hence, the
importance of N is projected to be high as the yield level is expected or projected higher in future
corn production.
1.3 CONCLUSIONS
Nitrogen is the essential nutrient required in greater amounts by plants and is often the most limit-
ing nutrient for crop production under most agroecosystems. In the future, increasing crop produc-
tion will depend more on N than any other nutrient. N prices have been increased significantly
in the past few decades. Under these situations, increasing crop yields per unit area through the
use of appropriate N management practices has become an essential component of modern crop
production. In addition, the efficient use of N is essential to reduce the cost of crop production and
also environmental pollution. N plays an important role in many morphological, physiological, and
biochemical processes in the plants. It is mainly responsible for improving growth yield and yield
components in cereals and legumes. The growth parameters that improve with the addition of N
are plant height, shoot dry weight, and root growth. All these growth traits have significant positive
association with grain yield in cereals and legumes. Similarly, yield components such as panicle
number and number of pods have significant positive association with grain yield. However, spikelet
sterility has significant negative association with grain yield. The influence of N is significant in the
assimilation of carbon in the source organs (especially leaves) and translocate and the utilization
of photosynthates in the sink organs (grains), which determines the growth rate and productivity
of crop plants. It is essential for photosynthesis in higher plants. Adequate N content in the leaves
improves RUE and consequently crop yields. In general, RUE is an independent measure that can
be used to benchmark crop performance and highlight yield limitations. Radiation use is a valuable
approach for interpreting large variations in crop yield from season to season and across locations
resulting from climatic variations.
