Effects of Grasshopper Frass and Bison Dung Additions on
Soil Nitrogen Pools in Ungrazed Konza Prairie Grassland
Jennifer L. Apple, Anthony Joern & John Blair
Grasshoppers may eat or clip from 10-35% of
aboveground net primary production. What other
consequences of insect herbivory are important
to ecosystem processes in grasslands?
250
Experimental manipulations of
grasshopper frass and bison dung
200
NO3-N
b
ab
150
Frass distribution by watershed
• Substantial variation among blocks in levels of ambient
frass deposited was observed (Fig. 5). The mean ambient
frass input was 2.6 g/m2.
• Total amount of frass deposited (Fig. 1) varies by
watershed and year, with more frass in 1-year vs. 4-year
burns in most years. No effect of grazing on frass
production is obvious.
• No relationship between nitrogen pools and levels of
ambient frass input (in the 10 control plots) was detected
(p>0.1).
• Correlations between average grasshopper density and
frass production varied between years (Fig. 2).
• Nitrogen pools did not differ among the three levels of
frass addition (ambient, ambient + 10 g/m2, & ambient +
20 g/m2) (Fig. 6).
50
0
100
NH4-N
ab
a
75
Pulse
Repeated
125
100
75
50
25
0
10
20
Frass amount (g/m2)
b
Figure 4
50
250
25
200
0
Bison dung
Frass
Control
Figure 3
5
4
3
100
50
0
100
50
1
25
1
2
3
4
5
6
7
8
9 10
NH4-N
75
2
0
NO3-N
150
Addition type
µg N per resin bag
• Amount and frequency of additions (pulse vs. repeated
applications) generally did not affect soil N pools for either
grasshopper frass or bison dung. A marginal effect of
amount (p<0.05) and frequency (p<0.09) by grasshopper
frass on NH4-N was detected in frass addition plots (Fig.
4).
100
2
Does grasshopper frass significantly
affect soil nitrogen levels?
g frass/m
• Addition of bison dung resulted in significantly lower NO3N (p<0.05) than in frass addition plots. NH4-N was lower
(p<0.1) in bison dung addition plots than in control plots.
Frass additions did not differ from control plots (Fig. 3).
µg N per resin bag
a
µg NH4-N per resin bag
Division of Biology, Kansas State University, Manhattan, KS
0
Ambient
Block
Figure 5
10
20
Frass amount
Figure 6
Conclusions
Methods: Natural frass deposition
5
Grasshopper frass production was estimated using frass traps at
Konza Prairie. Ten traps were placed randomly along each of 3 or
4 transects at replicated sites in K1B, N1B, K4B, and N4D
watersheds at upland sites. Frass production was estimated over
the course of a growing season ending in late September.
3
2
1
0
5
2004
• Decomposition of added frass provided more N to soil N
pools than did equal amounts of bison dung, but not more
than ambient frass input.
4
3
2
6
1
5
2005
4
3
2
• Grasshopper frass is not contributing greatly to grassland
nutrient dynamics at low to moderate densities. The
timing and fine-scale distribution in space suggests more
study is warranted. Little is known about how
grasshopper carcasses or greenfall from herbivory affect
grassland nutrient budgets.
4
3
2
1
1
0
2005
2003
5
0
Frass (g/m2)
We varied the amount and frequency of grasshopper frass or bison
dung in K1B to assess effects on soil N pools. In each of 10
blocks, grasshopper frass or crumbled bison dung was added to
0.1 m2 plots at either 10 g/m2 or 20 g/m2 rates as either a pulse
(single application on 15 July 2005) or repeated application (3
separate applications 3-4 weeks apart: 15 July, 5 Aug and 2 Sept).
We estimated ambient frass inputs through weekly collections from
5 frass traps per block. Soil N availability was measured using two
ion exchange resin bags buried about 5 cm deep in each plot.
Bags were retrieved after ~12 weeks (31 Oct 2005). Ion exchange
resins were extracted with 2N KCl; NO3-N and NH4-N were
determined on an Alpkem FlowSolution autoanalyzer.
• Significant amounts of grasshopper frass are deposited
each year at Konza Prairie, providing ~0.06 g N/m2 per
year. No clear relationship with fire or grazing activity was
observed among years, except to the degree that these
factors determine grasshopper densities.
4
Frass (g/m2)
Methods: Frass addition experiment
Frass trap
2003
0
K1B
Figure 1
K4B
Site
N1B
N4D
0
1
2
3
4
Grasshopper density (#/m 2)
Figure 2
5
Acknowledgments - We thank Meghan Dinkins and Rose Phillips for
help with resin bag extractions.