152
D. L. N. Rao et al.
chart may not be uniformly applicable to all varieties that differ in inherent leaf
color and regions that differ in climate, thereby necessitating individual or group
standardization in different cultivated areas. In the Soil Test-Crop Response (STCR)
methodology of site-specific nutrient management, recent development of algorithms
of leaf colour chart, SPAD and fieldscout CM 1000 m values at three critical growth
stages with yield in rice-wheat system showed promising results [19].
3.3 Product Based Approaches
3.3.1 Slow Release and Customized Fertilizers
Much of the nitrogen applied by farmers goes into the atmosphere as ammonia and to a
lesser extent as oxides of nitrogen. Phosphorus ends up in watersheds creating ideal
conditions for eutrophication. Installing precision systems based on autonomous
vehicles and sensors is costly, so only large-scale operations tend to have them. In
comparison, advanced controlled-release fertilizers are relatively inexpensive and
can ensure that significantly higher levels of nutrients reach the crops, leading to
higher yields with less fertilizer application. Slow-release fertilizers typically consist
of granules or tiny capsules filled with nutrients; they need to meet each of three
controlled release criteria, viz., not more than 15% release in 24 h, not more than 75%
release in 4 weeks and at least about 75% release at the stated release time. The most
popular are the condensation polymers-urea formaldehydes, urea isobutyraldehydes,
urea crotonaldehydes. These are water insoluble and N is slowly hydrolysed from the
polymer chain. The others are the coated ones like S-coated, polymer coated and latex
coated urea products. Here N is slowly released by diffusion through the coatings.
Gel based materials contain urea absorbed within acrylic gels for example. Urease
inhibitors (NTBT) and nitrification inhibitor incorporated urea materials (N-Serve,
DCD) are known for long. Sophisticated materials and manufacturing techniques
have been developed that can tune the outer shells and alter nutrient-release rates
in desired ways as the soil’s temperature, acidity or moisture changes. The global
consumption of controlled- and slow release fertilizers has increased at an average
annual rate of 30% during 2009–14. Polymer-coated urea is now one of the most
widely used controlled release products in arable cropping systems [105].
Although controlled-release technologies are more efficient, they do not eliminate
all the drawbacks of fertilizer use. The products still include ammonia, urea and
potash, for example; producing these substances is energy-intensive and contributes
to greenhouse gas production and climate change. However, the losses are mitigated.
They are more expensive, however sulphur coated urea is the least expensive. In a
field evaluation of coated and modified urea products for submerged rice in a sandy
loam soil in North India [72] the peak concentrations of ammoniacal N (AN) in
the floodwater (pH 9.5–10.0) were >12 g m
−3 and ammonia volatilization losses
were ~54% of applied N when 120 kg N ha
−1 were applied as a whole dose U(W).
When applied in 3 equally split doses U(S), peak AN levels reduced to ~5 g m
−3
D. L. N. Rao et al.
chart may not be uniformly applicable to all varieties that differ in inherent leaf
color and regions that differ in climate, thereby necessitating individual or group
standardization in different cultivated areas. In the Soil Test-Crop Response (STCR)
methodology of site-specific nutrient management, recent development of algorithms
of leaf colour chart, SPAD and fieldscout CM 1000 m values at three critical growth
stages with yield in rice-wheat system showed promising results [19].
3.3 Product Based Approaches
3.3.1 Slow Release and Customized Fertilizers
Much of the nitrogen applied by farmers goes into the atmosphere as ammonia and to a
lesser extent as oxides of nitrogen. Phosphorus ends up in watersheds creating ideal
conditions for eutrophication. Installing precision systems based on autonomous
vehicles and sensors is costly, so only large-scale operations tend to have them. In
comparison, advanced controlled-release fertilizers are relatively inexpensive and
can ensure that significantly higher levels of nutrients reach the crops, leading to
higher yields with less fertilizer application. Slow-release fertilizers typically consist
of granules or tiny capsules filled with nutrients; they need to meet each of three
controlled release criteria, viz., not more than 15% release in 24 h, not more than 75%
release in 4 weeks and at least about 75% release at the stated release time. The most
popular are the condensation polymers-urea formaldehydes, urea isobutyraldehydes,
urea crotonaldehydes. These are water insoluble and N is slowly hydrolysed from the
polymer chain. The others are the coated ones like S-coated, polymer coated and latex
coated urea products. Here N is slowly released by diffusion through the coatings.
Gel based materials contain urea absorbed within acrylic gels for example. Urease
inhibitors (NTBT) and nitrification inhibitor incorporated urea materials (N-Serve,
DCD) are known for long. Sophisticated materials and manufacturing techniques
have been developed that can tune the outer shells and alter nutrient-release rates
in desired ways as the soil’s temperature, acidity or moisture changes. The global
consumption of controlled- and slow release fertilizers has increased at an average
annual rate of 30% during 2009–14. Polymer-coated urea is now one of the most
widely used controlled release products in arable cropping systems [105].
Although controlled-release technologies are more efficient, they do not eliminate
all the drawbacks of fertilizer use. The products still include ammonia, urea and
potash, for example; producing these substances is energy-intensive and contributes
to greenhouse gas production and climate change. However, the losses are mitigated.
They are more expensive, however sulphur coated urea is the least expensive. In a
field evaluation of coated and modified urea products for submerged rice in a sandy
loam soil in North India [72] the peak concentrations of ammoniacal N (AN) in
the floodwater (pH 9.5–10.0) were >12 g m
−3 and ammonia volatilization losses
were ~54% of applied N when 120 kg N ha
−1 were applied as a whole dose U(W).
When applied in 3 equally split doses U(S), peak AN levels reduced to ~5 g m
−3