Agriculture Reference
In-Depth Information
2.8 FACTORS AFFECTING NITROGEN LOSSES
N losses from soil-plant system are influenced by climatic, soil, and plant factors and are also
influenced by N sources and methods of application. Climatic factors that influence N losses are
precipitation and temperature. Soil factors that influence N losses are soil pH and texture. N fertil-
izer sources and methods of application also influence N losses from soil-plant system. Plant factors
associated with N losses are fallow versus cropped lands.
2.8.1 p reCIpItatIon
Quantity and intensity of precipitation or rainfall during crop growth significantly influences N
losses from the soil-plant system. Heavy rainfall of longer duration in the early crop growth is
responsible for the leaching of the NO 3 -N from the plant root zone to the lower depths where it can-
not be absorbed by the plant roots. In the early growth stage, root growth of the crop plants is not
well developed and nitrified N is not assimilated. Hence, chances of loss through leaching are quite
high. N deficiency symptoms in upland rice grown in Brazilian Oxisols are often observed by the
author when rainfall is heavy after emergence of seedlings until the beginning of the tillering stage
that depends on genotype and climatic conditions. However, in most genotypes, tillering starts at
about 20 days after sowing in the central part of Brazil, locally known as Cerredo region (Fagreia
and Knupp, 2013).
The development of different growth stages in upland rice is given in Table 2.1. Fageria and
Knupp (2013) also reported that maximum root length followed a significant quadratic response
with the advancement of the plant age from 19 to 120 days after sowing. There was a linear increase
in the root length from tillering initiation to flowering. Thereafter, the root length was more or less
constant or reached to the plateau (Fageria and Knupp, 2013). An excess of soil moisture is also
responsible for the denitrification losses from the plant root zone or rhizosphere. Most of the N
losses due to leaching by rainfall occur in the humid and subhumid regions of the world where the
annual rainfall is high. For example, in the central part of Brazil, the average annual rainfall is about
1500 mm, mostly during the months of October to March. Hence, N leaching from the cropping
system is very common in this region.
TABLE 2.1
Timing (DAF, Days after Sowing) of Upland Rice Growth Stages and Definitions
Growth Stage
DAF
Definition
Germination
5
Defined as the stage when the coleoptile tip first became visible.
Tillering initiation
19
Defined as the crop growth stage when the first tiller from the main shoot is
visible.
Active tillering
45
Defined as the development stage at which maximum tillering rate per unit
time during crop growth.
Panicle initiation
61
Defined as the initiation of the panicle.
Booting
85
Defined as the development stage at which the panicle is enclosed by the
sheath of the uppermost leaf.
Flowering
95
Defined as the physiological stage at which flowers are visible on the
panicles.
Physiological
maturity
120
Defined as the growth stage at which grains are ripened and panicles are
ready for harvest.
Source: From Fageria, N. K. and A. M. Knupp. 2013. Plant Nutr. 36:1-14. With permission.
 
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