Agriculture Reference
In-Depth Information
Table 2.5
Rate of metabolism of dicyandiamide at three concentrations over time. (Source:
Rathsack
1978
)
Treatment
Time (days)
Milligram (mg) DCD-
nitrogen/100 g soil
0
14
28
42
56
70
84
98
6
4.0
5.7
6.2
6.8
10.5
12.0
12.4
12.1
4
4.0
4.8
6.0
8.5
9.8
9.8
10.6
10.3
2
4.0
4.8
6.9
7.7
8.4
7.9
8.8
9.4
0
4.0
4.0
4.5
5.8
5.9
6.5
6.0
5.8
Soil source = Wietzenbruch
of calcium cyanamide linked with its useful combination of calcium and nitrogen
and associated reduced rate of nitrification benefit soil fertility (Verona
1969
). In-
telligent application of fertiliser chemistry towards the greater exploitation of com-
pounds such as calcium cyanamide will retain the capacity for feeding the burgeon-
ing world population in ways which are environmentally sustainable.
Water Conservation
Water is an increasingly scarce resource worldwide and irrigated broad acre agricul-
ture remains one of its largest and frequently inefficient users (Costa et al.
2007
). All
intensive horticultural crops have very large demands for water in order to maintain
yield, quality and appearance. In the environmental and social sectors the continu-
ous availability of water in times of shortage in order to sustain the appearance of
landscapes is a more questionable priority. Nonetheless once the structure of a land-
scape is damaged by drought it is hugely difficult to return it to its original status.
Nonetheless low water-use efficiency (WUE) in some horticultural plants together
with an increasing competition for water resources with other sectors (e.g. domestic
uses, tourism or industry) is encouraging the adoption of new irrigation and culti-
vation practices that use water more judiciously. There have been very substantial
improvements in the economy with which water is used in horticulture over the last
20 years. These have utilised fundamental scientific knowledge describing the man-
ner by which plant growth regulators such as abscicic acid and cytokinins control
water losses through the stomata (Davies and Zhang
1991
; Wilkinson and Davies
2002
; Davies et al.
2005
).
In areas with dry and hot climates, drip irrigation and protected cultivation have
improved WUE mainly by reducing runoff and evapotranspiration losses (Jones
2004
). Greater precision in the control of water use is now being achieved by using
deficit irrigation strategies such as regulated deficit irrigation or partial root drying
have emerged as means of increasing water savings by allowing crops to withstand
mild water stress with no or only marginal decreases of yield and quality. Deficit ir-
rigation is where the volume of irrigation applied is less than that needed to replace
all evapo-transpiration losses and hence there is a net depletion of water from the
