Agriculture Reference
In-Depth Information
sive agricultural management (Fraterrigo et al., 2006 and Culman et al.,
2010), even in response to organic management (Williams and Hedlund,
2013). Indeed, in agricultural soils that are intensively managed, microbial
activity tends to change more quickly in response to organic management
than community composition (Burger and Jackson, 2003).
The overall objective of this study is to examine how soil physico-
chemical characteristics and nutrient management practices affect soil
microbial activity and microbial community composition in organic ag-
ricultural systems, using an on-farm approach with several participating
farmers. This study is part of a larger project examining plant-soil-micro-
bial interactions and multiple ecosystem functions across a set of organic
farms selected to be representative of the local landscape using geographic
information system (GIS) techniques (Bowles et al., ms. in preparation).
Thirteen organically-managed fi elds growing Roma-type tomatoes (
Sola-
num lycopersicum
L.) were selected in Yolo County, part of the Sacra-
mento Valley of California, an agricultural landscape dominated by high-
input conventional agriculture with a diverse array of crops. The focus is
on the period of maximal tomato nutrient demand when microbial activity
is most important for crop productivity. There were two main hypotheses.
First, farm fi elds would differ in soil microbial biomass and enzyme ac-
tivities, and these differences would depend on the quantity and composi-
tion of SOM as well as other factors related to the type of organic amend-
ments. Second, microbial community composition would be infl uenced by
nutrient management practices but with fewer differences across the fi elds
relative to enzyme activities given the overall lack of diversity in the soil
biota in this landscape, which appears to be related to high disturbance and
low complexity ( Culman et al., 2010).
The specifi c objectives of this study are to: 1) characterize the variabil-
ity of soil properties and organic management practices across a number
of organically-managed Roma-type tomato fi elds; 2) determine patterns
of soil enzyme activities and fatty acid methyl esters (FAMEs) to indicate
microbial community composition and relate them with soil properties
and management practices; and 3) consider the implications for micro-
bially-derived ecosystem functions for management of different types of
organic farms across this landscape. On 13 organic fi elds differing in nutri-
ent management practices, soil physicochemical characteristics; microbial
