Agriculture Reference
In-Depth Information
16.6 DECLINING NUE: A SERIOUS CONCERN
Fertilizer consumption increased 322 times in India between 1950 and 1951 and
2007 and 2008. Yet, the fertilizer use efficiency is extremely low. The yield curve
in most irrigated crops has plateaued because of the stagnated response to added
inputs. Nonetheless, because of a large yield gap, there exists a vast potential to
enhance the crop yields in rainfed agriculture. The potential yield of sorghum in
research plots is about 3970 kg ha
-1
compared with the average yield of 2090 kg
ha
-1
in verification trials. However, the average yield levels in rural farms are as
low as 370 kg ha
-1
. Data from on-farm trials conducted under the Simple Fertilizer
Trials Scheme of the Indian Council of Agricultural Research (ICAR) show that the
response ratio is the highest for N (11.6 to 16.7 kg grain/kg N), followed by that of
P (5.5 to 12.5 kg grain/kg P
2
O
5
), and the least for K (3.6 to 6.2 kg grain/kg K
2
O).
Furthermore, response to nitrogen-phosphorus (NP), nitrogen-potassium (NK), or
NPK is not additive of their individual responses, which leads to an excessive use of
N. The rate of nutrient application in these trials is high (120 kg N + 60 kg P
2
O
5
+ 60
kg K
2
O), and although the increase in yield of wheat by fertilizer use is much higher
(1.1 to 2.6 Mg ha
-1
compared to 0.47 to 1.25 Mg ha
-1
for tall varieties), the response
ratio to NPK application is low and ranges from 4.7 to 10.9 kg grain/kg of nutrients.
16.7 IMPORTANCE OF SOC
World soils are among the Earth's largest terrestrial reservoirs of C and have a
large potential of C sequestration. Thus, C sequestration in agricultural soils is
an important strategy of reducing atmospheric concentration of CO
2
(Lal 2004).
Further, sequestration of C in agricultural soils has numerous cobenefits in terms
of increased soil fertility and environmental quality. Because soils under rainfed
cropping are severely depleted of their SOC stock and are strongly degraded, there
is a large potential for C sequestration (Wani et al. 2003). Low SOM level in tropi-
cal soils, particularly in those of arid, semiarid, and subhumid climates, is a major
determinant of low productivity (Syers et al. 1996; Katyal et al. 2001). Therefore,
proper management of SOM is important to sustaining productivity, ensuring food
security, and restoring marginal lands (Scherr 1999). With a low fertilizer input in
dryland agriculture, mineralization of SOM is a major source of plant nutrients. Yet,
maintaining or improving SOM levels in soils of the tropics is difficult because of
a high rate of oxidation under prevailing high temperatures (Lal 1997; Lal et al.
2003). Nonetheless, maintaining or improving SOM level is a necessary prerequisite
to improving soil quality, productivity, and sustainability.
The SOC balance of terrestrial ecosystems is changed markedly by human activi-
ties—including deforestation, biomass burning, and land use change, which result
in the emission of trace gases that enhance the “greenhouse effect” (Bolin 1981;
Trabalka and Reichle 1986; IPCC 1990; Batjes 1996; Bhattacharya et al. 2000;
Lorenz and Lal 2005). Routinely, soil surveys estimate SOC pool to 0.5- to 1-m
depth. However, SOC can be sequestered in subsoil (>1-m depth) by selecting plants/
cultivars with deeper and thicker root systems that are high in recalcitrant com-
pounds like suberin and lignin (Wani et al. 2003; Lorenz and Lal 2005).
Search WWH ::
Custom Search