Values and Services of Nitrogen-Fixing Alder Based Cardamom Agroforestry Systems in the Eastern Himalayas - Smallholder Tree Growing for Rural Development and Environmental Services - page 383

Table 18.2 Annual input and out of energy and cash in cardamom based agroforestry systems
Sharma R et al. 2002)
Input/output Energy (×10 4 kJ ha −1 ) Cash (US$ ha −1 )

Alder- Forest- Alder- Forest-

cardamom cardamom cardamom cardamom

Input
Weeding 2.1 4.2 2.8 5.6

Harvest 8.4 4.2 11.2 5.6

Post-harvest 42 21 56 28

Fire-wood collection 13 6 17 8

Fire-wood used in curing 1,064 465 35 17

Total 1,129 501 121 65

Output
Agronomic yield 920 411 2,112 a 954 a

Fire-wood extraction 3,087 1,486 101 56

Fodder - 596 - 7

Total 4,007 2,493 2,213 1,017

Output:Input ratio 3.55 4.98 18.23 15.67

Human labour per hour was calculated at 0.15 × 10 4 kJ (Freedman 1982)
a Calculated at US$4.65 per kilogram of cardamom and cash conversion @ US$1 = Indian Rs. 43.

18.3.2 Nitrogen Fixation and Nutrient Use Efficiencies

Nitrogen accretion through biological fixation following acetylene reduction assay,
and then applying the C 2 H 2 : N 2 conversion factor of 2.4: 1, was used to estimate
nitrogen fixation (Hardy et al. 1973; Sharma and Ambasht 1988). In pure planta-
tions of Himalayan alder, the annual accretion was highest (117 kg ha −1 year −1 ) in
the seven-year stand and lowest (29 kg ha −1 year −1 ) in the 56-year stand (Sharma
and Ambasht 1984, 1988; Sharma et al. 1998a). The Himalayan alder fixed 65 kg
nitrogen ha −1 year −1 , benefiting the associated cardamom in the alder-cardamom
system (Sharma and Purohit 1996). In the age series of the alder-cardamom agro-
forestry system, nitrogen fixation ranged from 52 to 155 kg ha −1 year −1 (highest at
the age of 15-years) suggesting a substantial input of nitrogen into the system by
alder (Sharma 2001).
The nutrient use efficiency is the ratio of the annual net primary productivity and
the nutrient uptake. The nitrogen use efficiency was 73 and 93; phosphorus was 823
and 1,151 for the alder-cardamom and forest-cardamom stands respectively (Table
18.1). In the case of the age series of the alder-cardamom systems, the nitrogen use
efficiency was 98 for the five-year-old stand and 81 for the 40-year-old stand.
Similarly, the efficiency use of phosphorus decreased with age, being 2,439 for the
5-year-old stand and reaching a minimum value of 1914 for the 40-year-old stand.
The average phosphorus use efficiency in all aged stands was approximately 25
times greater than the nitrogen use efficiency (Sharma et al. 2002b).
A drop in nutrient use efficiency should be expected with ageing tree-crop sys-
tems as the utilization of a given nutrient (i.e., the nutrient uptake) increases over