146
D. L. N. Rao et al.
pollution and climate change-nitrate leaching, ammonia volatilization and denitrification. N recommendation based on soil analysis that takes into consideration of
soil nitrate or any other available N sources reduces the amount of needed N and
improves efficiency.
Precision agriculture has been especially helpful in tackling fertilizer loss, a major
concern for farmers, as nitrogen fertilizer is one of their biggest expenses. Recent
results on variable N application to wheat in Yaqui Valley, Mexico [57] show that
N fertilizer rate reductions from rates (300 kg N ha
−1 ) to the economic optimum
rates (123 and 145 kg N ha
−1 ) can significantly improve N use efficiency, from 36–
39% at higher rates to 50–57% at optimum rates and also reduce N 2 O emissions
(avoiding the equivalent to 0.5–0.8 Mg CO 2 e ha
−1 yr
−1 or, regionally, 84–138 Gg
CO 2 e yr
−1 ) without compromising yields. Basso et al. [7] analyzed eight years’ worth
of satellite data that covered corn- and soybean fields spread across 30 million ha
of Midwestern states of USA and showed that only about 50% of the cropland is
high-yielding, the remaining half is either of consistently low-yielding fields (26%)
or those that produce a mix of low and high yields (28%). So, only half the nitrogen
in the fertilizer that had been applied was actually taken up by the plants and the rest
50% lay wasted in the soil, or lost as greenhouse gases or swept up by rainfall into
waterways. They concluded that streamlining the fertilizer usage can save US corn
and soybean farmers an estimated $500 million in fertilizer costs, and stop 6.8 million
metric tons of carbon dioxide equivalent escaping from unused nitrogen fertilizer into
the atmosphere. Availability of several soil-crop simulation models paved the way
for effective N management and assessment of NUE and N losses. These models
integrate the effect of soil, weather, cultivar, pest, and other management practices
on the growth and yield of crop [98].
3.1 Soil Based Approaches
Proper management of fertilizers is aimed at increasing the system productivity,
farmer profitability, enhanced environmental protection and improved sustainability.
Other agronomic and conservation practices, such as no-till farming and the use of
cover crops, play a valuable role in supporting best nutrient management practices.
3.1.1 Soil Testing and Crop Response
In conventional soil testing programs, a set of critical values that characterize the
estimates of soil available nutrients as low, medium or high serve as an empirical
guide to rates of fertilizer application for various crops and are used by soil testing
laboratories in India. The generalized recommendations of fertilizer use are applicable to the medium category of soil testing estimates with an arbitrary adjustment
(decrease or increase by 25–50%) for high and low categories of soil test estimates.
This classical approach relies only on the soil analysis and does not take into account
D. L. N. Rao et al.
pollution and climate change-nitrate leaching, ammonia volatilization and denitrification. N recommendation based on soil analysis that takes into consideration of
soil nitrate or any other available N sources reduces the amount of needed N and
improves efficiency.
Precision agriculture has been especially helpful in tackling fertilizer loss, a major
concern for farmers, as nitrogen fertilizer is one of their biggest expenses. Recent
results on variable N application to wheat in Yaqui Valley, Mexico [57] show that
N fertilizer rate reductions from rates (300 kg N ha
−1 ) to the economic optimum
rates (123 and 145 kg N ha
−1 ) can significantly improve N use efficiency, from 36–
39% at higher rates to 50–57% at optimum rates and also reduce N 2 O emissions
(avoiding the equivalent to 0.5–0.8 Mg CO 2 e ha
−1 yr
−1 or, regionally, 84–138 Gg
CO 2 e yr
−1 ) without compromising yields. Basso et al. [7] analyzed eight years’ worth
of satellite data that covered corn- and soybean fields spread across 30 million ha
of Midwestern states of USA and showed that only about 50% of the cropland is
high-yielding, the remaining half is either of consistently low-yielding fields (26%)
or those that produce a mix of low and high yields (28%). So, only half the nitrogen
in the fertilizer that had been applied was actually taken up by the plants and the rest
50% lay wasted in the soil, or lost as greenhouse gases or swept up by rainfall into
waterways. They concluded that streamlining the fertilizer usage can save US corn
and soybean farmers an estimated $500 million in fertilizer costs, and stop 6.8 million
metric tons of carbon dioxide equivalent escaping from unused nitrogen fertilizer into
the atmosphere. Availability of several soil-crop simulation models paved the way
for effective N management and assessment of NUE and N losses. These models
integrate the effect of soil, weather, cultivar, pest, and other management practices
on the growth and yield of crop [98].
3.1 Soil Based Approaches
Proper management of fertilizers is aimed at increasing the system productivity,
farmer profitability, enhanced environmental protection and improved sustainability.
Other agronomic and conservation practices, such as no-till farming and the use of
cover crops, play a valuable role in supporting best nutrient management practices.
3.1.1 Soil Testing and Crop Response
In conventional soil testing programs, a set of critical values that characterize the
estimates of soil available nutrients as low, medium or high serve as an empirical
guide to rates of fertilizer application for various crops and are used by soil testing
laboratories in India. The generalized recommendations of fertilizer use are applicable to the medium category of soil testing estimates with an arbitrary adjustment
(decrease or increase by 25–50%) for high and low categories of soil test estimates.
This classical approach relies only on the soil analysis and does not take into account