Plant Demand Adapted Fertilization in Organic and Precision …
151
3.2.2 Plant Improvement
Knowledge on improving nitrogen use efficiency and its components and the key
molecular players in N uptake, assimilation, and utilization has grown significantly
[43, 96] however, improving the efficiency of these processes has proved difficult. Improving the crop N use-efficiency (NUE) requires in-depth understanding of
unknown co-regulatory mechanisms integrating growth, N assimilation and carbon
(C) fixation. Li et al. [48] showed that balanced opposing activities and physical
interactions of the rice Growth-Regulating Factor 4 (OsGRF4) transcription factor
and the DELLA growth-inhibitor confer homeostatic co-regulation of growth, C
and N metabolism. OsGRF4 promotes and integrates N assimilation, C fixation and
growth, whilst DELLA inhibits them. The DELLA proteins are a family of putative
transcriptional regulators that inhibit the cell proliferation and expansion that drives
the growth of plant organs. In consequence, the DELLA accumulation characteristic
of the green revolution varieties (GRVs) confers yield-enhancing dwarfism, but also
reduces NUE. Plant growth is stimulated via destruction of DELLA proteins in the
26S proteasome. However, GRV NUE and grain yield are increased by tipping the
OsGRF4-DELLA balance towards increased OsGRF4 abundance. Modulation of
plant growth and metabolic co-regulation thus enables novel breeding strategies for
future sustainable food security and a new Green Revolution.
Swarbreck et al. [93] have provided a roadmap to integrate the regulation of
nitrogen uptake and assimilation into varietal selection and crop breeding programs.
The overall goal is to reduce nitrogen inputs by farmers growing crops in contrasting
cropping systems around the world, while sustaining yields and reducing greenhouse
gas (GHG) emissions. Considering N responsiveness and its underlying mechanistic
regulation, as well as the introduction of varietal or advance breeding line screening
varieties for low N requirement and highly responsive varieties in crop breeding
pipelines, is likely to provide new means to develop new varieties with a low economic
N optimum.
3.2.3 Leaf Colour
Site specific N management studies using chlorophyll meter, have shown that N
savings can be effected along with improved plant N use efficiency [88]; their results
on wheat recommended application of 30 kg N ha
−1 as basal dose, 45 kg N ha
−1 at
crown root initiation and 30 or 45 kg N ha
−1 at maximum tillering depending on leaf
color as opposed to blanket dose of 120 kg N ha
−1 in two equal splits at planting
and CRI. Simple leaf color charts (LCC) have been developed for rice and wheat
[40, 85, 100] as a useful low-cost tool to support decision making on the timing and
quantity of N fertilizer application. The graded panels with differing shades of green
are compared with the colour of the adaxial leaf surface. It is of low cost and easy to
use to assess the N requirement of the crop. The dissemination of this low-cost tool
to a model village in Punjab has led to a reduction in N application of an average
of 75 kg N ha
−1 in rice and 50 kg N ha
−1 in wheat. However, the use of leaf color
151
3.2.2 Plant Improvement
Knowledge on improving nitrogen use efficiency and its components and the key
molecular players in N uptake, assimilation, and utilization has grown significantly
[43, 96] however, improving the efficiency of these processes has proved difficult. Improving the crop N use-efficiency (NUE) requires in-depth understanding of
unknown co-regulatory mechanisms integrating growth, N assimilation and carbon
(C) fixation. Li et al. [48] showed that balanced opposing activities and physical
interactions of the rice Growth-Regulating Factor 4 (OsGRF4) transcription factor
and the DELLA growth-inhibitor confer homeostatic co-regulation of growth, C
and N metabolism. OsGRF4 promotes and integrates N assimilation, C fixation and
growth, whilst DELLA inhibits them. The DELLA proteins are a family of putative
transcriptional regulators that inhibit the cell proliferation and expansion that drives
the growth of plant organs. In consequence, the DELLA accumulation characteristic
of the green revolution varieties (GRVs) confers yield-enhancing dwarfism, but also
reduces NUE. Plant growth is stimulated via destruction of DELLA proteins in the
26S proteasome. However, GRV NUE and grain yield are increased by tipping the
OsGRF4-DELLA balance towards increased OsGRF4 abundance. Modulation of
plant growth and metabolic co-regulation thus enables novel breeding strategies for
future sustainable food security and a new Green Revolution.
Swarbreck et al. [93] have provided a roadmap to integrate the regulation of
nitrogen uptake and assimilation into varietal selection and crop breeding programs.
The overall goal is to reduce nitrogen inputs by farmers growing crops in contrasting
cropping systems around the world, while sustaining yields and reducing greenhouse
gas (GHG) emissions. Considering N responsiveness and its underlying mechanistic
regulation, as well as the introduction of varietal or advance breeding line screening
varieties for low N requirement and highly responsive varieties in crop breeding
pipelines, is likely to provide new means to develop new varieties with a low economic
N optimum.
3.2.3 Leaf Colour
Site specific N management studies using chlorophyll meter, have shown that N
savings can be effected along with improved plant N use efficiency [88]; their results
on wheat recommended application of 30 kg N ha
−1 as basal dose, 45 kg N ha
−1 at
crown root initiation and 30 or 45 kg N ha
−1 at maximum tillering depending on leaf
color as opposed to blanket dose of 120 kg N ha
−1 in two equal splits at planting
and CRI. Simple leaf color charts (LCC) have been developed for rice and wheat
[40, 85, 100] as a useful low-cost tool to support decision making on the timing and
quantity of N fertilizer application. The graded panels with differing shades of green
are compared with the colour of the adaxial leaf surface. It is of low cost and easy to
use to assess the N requirement of the crop. The dissemination of this low-cost tool
to a model village in Punjab has led to a reduction in N application of an average
of 75 kg N ha
−1 in rice and 50 kg N ha
−1 in wheat. However, the use of leaf color