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Seasonal variation of feed values in arid mountain grasslands under grazing impact in
Qilian Shan, NW China
•Qilian Mountains are placed in between Qinghai and Gansu provinces of North West China. Being a northern outlier of Kunlun Mountains, they borders with Tibetan Plateau. • Qilian Mountains belongs to semi-arid dryland where precipitation and temperature – are two main factors determining vegetation cover - show a distinct vertical gradient•Strong differentiation of vegetation on North-facing slopes (mostly spruce forest -Picea crassifolia) and dry South-facing slopes with sparse vegetation.
to evaluate the variation in pasture quality and its dependence from environmental and landscape-related factors as well as from management characteristics (vegetation inventories).
to assess grazing-induced and spatially differentiated changes in vegetation patterns regarding to species composition, productivity and grazing value.
The objective of the research was: to examine feed values of spring/autumn and summer
pastures with subject to harvest time (1) and grazing intensities (2) along the altitudinal gradient and
to examine if grassland ecosystem suffer under degradation due to continues grazing and trampling pressure.
2003
2012
Stellera chamaejasme
Iris ensata
Xanthopappus subacaulis
For grazing value estimation was developed applied range condition scale (visual estimation scale and complex degradation index)Productivity: 2-years data on biomass wet and dry weight (235 samples), among them 115 samples were used in analyses for the feeding values (ADF, NDF, ADL) and inorganic content (macro and tracing elements)
Du Toit has suggests to estimated chemical parameters (TDM, ADF, K, Mg, Ca, N, P) of each of the forage species in order to
model the forage values for each specie presented in the pasture community by multiplying with spread total cover value to get the
agronomic value of grazing index.
ADF – Acid Detergent Fiber – the amount of indigestible forage.
NDF – Neutral Detergent Fiber – the amount of forage which could be digested
CP = Crude Protein = Nitrogen x 6,25Effective size - amount of biomass
consumed by herbivores. Effective size = (wet weight – dry weight)/ wet weight
Effect of harvest time
1 2 3
0.5
0.6
0.7
0.8
Effective size variaton during growing season
harvest
effe
ctsi
ze,g
m²
1 2 3
45
50
55
60
65
NDF values variaton during growing season
harvest
ND
F,%
1 2 3
22
24
26
28
30
32
34
ADF values variaton during growing season
harvest
AD
F,%
…on effective size of the biomass
…on NDF values …on ADF values
…on Crude Protein
1 2 3 4
45
50
55
60
65
Effect of grazing on NDF
grazing classes
ND
F,%
1 2 3 4
22
24
26
28
30
32
34
Effect of grazing on ADF
grazing classes
AD
F,%
1 2 3 4
05
00
10
00
15
00
Effect of grazing on biomass
grazing classes
we
t we
igh
t,g/m
²
…on biomass wet weight
…on NDF and ADF values …on number of species
0 500 1000 1500
05
10
15
20
Effect of species number on biomass
wet
spp
.no
1 2 3 4
51
01
5
Species number variation
grazing classes
spe
cie
s n
um
be
r
1 2 3 4
45
50
55
60
65
Effect of grazing on NDF
grazing classes
ND
F,%
1 2 3 4
22
24
26
28
30
32
34
Effect of grazing on ADF
grazing classes
AD
F,%
Carex spp, Medicago hyspida, Potentilla anserina, P. saundersiana,
P. bifurca, Kobresia capillifolia, Leymus secalinus,, Agropyron
crystatum
Medicago hyspida, Poa spp., Potentilla anserina, Geranium
pratense, Agroopyron cristatum, Stipa capillata,
Poligonum bistorta
Stipa capillata, Stellera shamaejasme, Oxytropis spp,
Heteropappus altaicus, Atriplex spp.
Stipa capillata, Medicago hyspida, Stellera shamaejasme, Artemisia spp., Oxytropis spp,
Allium cyaneum
1
2
3
4
2600 2800 3000 3200
50
01
00
01
50
0
peak biomass
Altitude
we
t
0 500 1000 1500
01
00
20
03
00
40
0
Growing season biomass
wet
dry
0 500 1000 1500
05
10
15
20
25
30
Effect of plant hight on biomass
wet
me
an
.h
Distribution of dry and wet biomass
wet vs dry weight
1 2 3
68
1012
1416
18
Mean hight variation
grazing classes
mea
n hi
ght
1 2 3 4
05
00
10
00
15
00
Effect of grazing on biomass
grazing classes
we
t we
igh
t,g/m
²
1 2 3 4
05
00
10
00
15
00
Effect of grazing on biomass
grazing classes
we
t we
igh
t,g/m
²
mean height vs dry weightdry weight vs altitude
r²=0,77 p<0,001
r²=0,50 p<0,001
12
34
0 500 1000 1500 Effe
ct o
f gra
zing
on
bio
ma
ss
gra
zing cla
sses
wet weight,g/m²
12
34
0 500 1000 1500 Effe
ct o
f gra
zing
on
bio
ma
ss
gra
zing cla
sses
wet weight,g/m²
r²=0,39 p<0,001
Median concentrations for the macro elements during growing season were P 1.470, Ca 7.97, K 18.58, Mg 2.51, S 2.21 in g/kg DM, and the trace elements were Mn 0.07, Fe 1.44, Zn 0.052 in g/kg DM. Median content of feed values was NDF 55.31%, ADF 27.45%, ADL 5.69%, CP 14.50% and median content of DM 126.82 gm²
There was no significant difference in seasonal variation of most mineral concentrations, except K (p=0,048) and Zn (p=0,0002), whereas feed values were differing significantly between harvests (p<0,05). Among grazing classes feed values were also significantly different (p<0,01), as well Zn, P and S content.
No linearity was observed in relationship between feeding values and grazing classes, although mean height of the standing biomass showed linear relation with grazing intensities (R²=0.35, p=0,008).