1
Biochar and manure amendments impact soil nutrient contents and microbial enzymatic activity in a
semi-arid irrigated maize cropping system
Erika J. Foster
a,b
, Neil Hansen
c
, Matt Wallenstein
b,d
, M. Francesca Cotrufo
a,b
a
Department of Soil and Crop Sciences, 307 University Avenue, Colorado State University, Fort Collins,
Colorado 80523, USA
b
Natural Resource Ecology Laboratory, 1232 East Drive, Colorado State University, Fort Collins, Colorado
80523, USA
c
College of Life Sciences, Brigham Young University, Provo, UT 84602, USA
d
Department of Ecosystem Science and Sustainability, Colorado State University, Fort Collins, Colorado
80523, USA
Corresponding author: Tel. 1-503-913-4532
Email address: Erika.foster@colostate.edu (E.J. Foster)
© 2016. This manuscript version is made available under the Elsevier user license
http://www.elsevier.com/open-access/userlicense/1.0/
2
Abstract
To mitigate negative impacts on crop yield from water-saving limited irrigation, we tested the effect of
two organic amendments on soil water holding capacity and nutrients. In an experimental maize field in
northern Colorado, we tilled in conventional steer manure (30 Mg ha
-1
) and a fast-pyrolysis pine-wood
biochar (30 Mg ha
-1
). We quantified impacts on soil moisture, total carbon and nitrogen, mineral
nitrogen, available phosphorus, microbial biomass, and seven extracellular enzymatic activities (EEAs).
Compared to the control, manure amendments increased gravimetric soil moisture by approximately
15%, total nitrogen by 10%, available phosphorus by 45%, and microbial biomass carbon by 15%
(p<0.05). Relative to the control, biochar increased total soil carbon by 80% and altered EEAs (p<0.05).
Biochar significantly increased α-1,4- glucosidase, β-D-cellobiohydrolase and β-1,4-N-
acetylglucosaminidase and significantly decreased β-1,4-glucosidase and phosphatase activities
(p<0.05). Despite the effects on soil moisture, nutrient availability, and microbial dynamics, neither
amendment significantly impacted maize yield under limited irrigation. Ongoing measurements will
allow us to fully assess longer-term impacts on yield.
Key Words: biochar; manure; extracellular enzymes; irrigation; microbial nutrient cycling; corn
3
1. Introduction
Increasing drought and competition for water resources among municipal, industrial, and agricultural
sectors requires improved water conservation in semi-arid regions. Agricultural producers can reduce
water use by adopting limited irrigation strategies (DeJonge et al., 2011; Fereres and Soriano, 2007),
such as applying irrigation only at critical crop growth phases (Schneekloth et al., 2009). To enhance soil
water retention under limited irrigation, traditionally, producers have treated soils with organic
amendments, such as manure (Bulluck III et al., 2002). Alternatively, recent research indicates that a
charcoal-like amendment, known as biochar, can have similar effects under limited irrigation, increasing
soil volumetric moisture content even with reduced water inputs (Akhtar et al., 2014).
Biochar is created through the pyrolytic conversion of any organic feedstock in an oxygen limited
environment, at temperatures >250°C (Lehmann and Joseph, 2015). The resulting product consists of
highly stable condensed aromatic carbon (C) rings, with physiochemical characteristics that depend on
pyrolysis conditions and feedstock type (Enders et al., 2012). This high variability in characteristics
necessitates the investigation of different biochars in various soil types and climatic regions to
determine which biochar can effectively achieve particular management goals (Novak et al., 2014). For
example, use of biochar co-generated from bioenergy production from local feedstock in our study
system in Colorado may also have additional environmental and cost benefits (Field et al., 2013)
compared to conventional amendments.
With high organic C content, both manure and biochar could have similar impacts on soil nutrients,
structure, and microbial dynamics in agricultural systems. Soil fertility research has long established that
manure amendments add nutrients to soils (e.g. organic N or ammonium (NH
4
+
)) and also improve soil
structure, therefore increasing nutrient retention and water holding capacity (Salter and Williams, 1968;
4
Ware and Johnson, 1949). These changes can benefit crop production by improving nutrient cycling via
stimulation of microbial growth and activity (Bulluck III et al., 2002; Elzobair et al., 2016; Peacock et al.,
2001). Active soil microbes metabolize and turnover organic matter, secreting specific extracellular
enzymes to break down large organic molecules into monomers, also available for plant uptake (Burns,
1982). Since specific enzymes are known to cycle C, N, and P substrates, shifts in extracellular enzymatic
activities (EEAs) are often used as a proxy for changing metabolic pathways and thus microbial function
in soils (Bell et al., 2013). The addition of organic material such as manure increases available C in the
soil, which causes growth in microbial biomass (Witter et al., 1993), and can increase the production and
activity of extracellular enzymes (Burns et al., 2013a). As a high C substance, with a large surface area
and porosity, biochar also has the potential to similarly influence soil structure and nutrient retention,
and thus microbial biomass and subsequent enzymatic activity.
In temperate agriculture, biochar addition influences microbial dynamics through physical changes to
soil structure and through chemical changes to soil stoichiometry and pH (Ippolito et al., 2012; Lehmann
and Joseph, 2015; Quilliam et al., 2013; X. Wang et al., 2015). By augmenting soil surface area and
porosity, biochar can increase soil water holding capacity (Brockhoff et al., 2010), and provide habitat
and relief from predation for microbes (Jaafar et al., 2015). Aside from physical habitat, biochar’s large
surface area and reactivity attracts ions and low-molecular weight organic compounds; thus biochar can
initially increase nutrient retention and potential sites for microbe-substrate interactions (Gul et al.,
2015). Even with these known structural changes, the effect of pine-wood biochar on microbial biomass
remains variable, ranging from no impact to 100% increases (Brantley et al., 2015; Domene et al., 2014;
Gomez et al., 2014; Jin, 2010). Despite the wide variation in response of microbial biomass to biochar,
few researchers have quantified how microbial function is altered by these induced soil physical changes
in soil moisture and surface area, and chemical changes to nutrient retention and pH (Elzobair et al.,
5
2016; Lehmann et al., 2011; Oleszczuk et al., 2014). Previous methods have quantified microbial
functional shifts and changes to nutrient cycling by measuring EEAs (Bell et al., 2013; Burns et al.,
2013b).
Enzyme activity is sensitive to pH and typically changes with nutrient dynamics, so quantification of
these proteins can further our understanding of biochar’s impact on microbial function and overall soil
fertility. Current research on biochar-enzyme interactions assesses soil chemistry and stoichiometry.
Since biochar can influence soil pH (alkaline pine biochar can lime soils by 1.0-1.4 units (Rogovska et al.,
2014)), it can impact enzymatic activities that function within restricted pH ranges. The pH effect
depends on the chemical composition of the biochar, which also can influence soil nutrients. Biochar
addition alters soil stoichiometry due to the large organic C inputs. This increase of C in some temperate
ecosystems can lead to an increase in microbial nitrogen (N) immobilization into biomass by up to three-
fold (Güereña et al., 2012) and subsequent N stabilization on biochar surfaces (Brantley et al., 2015),
although biochar addition does not always induce N immobilization (M.L. Cayuela et al., 2013). Biochar
effects on N dynamics and N-cycling enzymes remains ambiguous (Bailey et al., 2002), as even soil N
mineralization has been shown to decrease (Lentz et al., 2014), increase (Domene et al., 2014), and
remain unchanged (Gaskin et al., 2010) after biochar addition. Recent biochar studies also show variable
impacts on soil P: one greenhouse trial demonstrated no impact on soil P (Domene et. al 2014), a short
incubation suggested biochar alters colloidal particles and P retention (Soinne et al., 2014), and another
column study suggested that biochar lowered P bioavailability due to adsorption of orthophosphate and
organic P compounds to its surface (Laird et al., 2010). Yet another consideration for nutrient
stoichiometry and enzyme interactions is that biochar contains a small labile component that can
provide readily available nutrients for soil microbes and stimulate activity (Anderson et al., 2011;
Lehmann et al., 2011; Spokas et al., 2012; Warnock et al., 2007). These variable nutrient dynamics from