To save content items to your account,
please confirm that you agree to abide by our usage policies.
If this is the first time you use this feature, you will be asked to authorise Cambridge Core to connect with your account.
Find out more about saving content to .
To save content items to your Kindle, first ensure email@example.com
is added to your Approved Personal Document E-mail List under your Personal Document Settings
on the Manage Your Content and Devices page of your Amazon account. Then enter the ‘name’ part
of your Kindle email address below.
Find out more about saving to your Kindle.
Note you can select to save to either the @free.kindle.com or @kindle.com variations.
‘@free.kindle.com’ emails are free but can only be saved to your device when it is connected to wi-fi.
‘@kindle.com’ emails can be delivered even when you are not connected to wi-fi, but note that service fees apply.
Site properties and weed species abundance are known to vary spatially across fields. The extent to which they covary is not well understood. The objective of this research was to assess how canonical correlation analysis could be used to identify associations among site properties and weed species abundance within an agricultural field. A farmer-managed field rotated between Zea mays and Glycine max in Boone County, IA, was grid-sampled for site properties in 1992 and for weed species abundance between 1994 and 1997. Twelve site properties were considered in relation to five weed species that were identified and counted after all weed control operations were completed. Site properties such as total nitrogen, Bray-1 P, percent organic carbon, and texture were spatially variable. Weed species abundance was also spatially variable such that most weeds were found in patches and much of the field was weed-free. Canonical correlation analysis identified one to four significant correlations between linear combinations of site properties and weed species abundance. The first and second pairs of linear combinations explained the majority of variation in the data and were used to identify associations among site properties and weed species abundance. In years with Z. mays, the first pair of linear combinations described an association between herbicide activity and weed presence, and the second described topography and soil texture associations with weed presence. In years with G. max, the single observed association described a link between soil texture and presence of Setaria species and Polygonum coccineum. Several consistent associations were identified across years, indicating that site properties can influence weed abundance. However, annual variation in the associations may be attributed to differences in agronomic and weed management practices for each crop, as well as temporal weather variation influencing weed abundance from year to year. This multivariate technique is an important tool to identify associations between site properties and weed abundance that could help explain observed patchy patterns of weed abundance. These associations are an important first step in the generation of hypotheses to be tested at the whole field scale.
Hoop structures bedded with crop residues are becoming increasingly popular for swine production in the northcentral United States. Compost made from bedding materials and swine manure can be used as a soil amendment. A 3-yr field experiment was conducted in Boone, IA, to determine how composted swine manure affected selected soil characteristics and nutrient uptake, growth, and seed production of corn and three weed species (giant foxtail, velvetleaf, and common waterhemp) grown in mixture with corn. Two soil management systems, designed to provide equivalent amounts of N to corn, were compared: one that received composted manure and an average of 118 kg N ha−1 as synthetic fertilizer and another that received no composted manure and an average of 143 kg N ha−1 as synthetic fertilizer. Soil organic matter, P, K, and early-season NO3-N levels were greater in the (+) compost system. The N concentration of velvetleaf shoots, the P concentration of giant foxtail and common waterhemp shoots, and the K concentration of shoots of all three weed species also were greater in the (+) compost system. Compost application consistently increased common waterhemp height, common waterhemp biomass, and velvetleaf height, but increased velvetleaf biomass in only 1 yr and had no effect on giant foxtail height or biomass. Measurements of weed seed production, conducted in the final year of the study, showed that compost increased velvetleaf and common waterhemp seed production but had no effect on giant foxtail seed production. Compost consistently increased corn height and leaf K concentration but generally had no effect on corn yield. Results of this study indicate that large differences can exist among crop and weed species in their response to soil amendments. Depending on the weed species present, use of composted swine manure may increase requirements for weed management in corn production systems.
The soil carbon (C) pool constitutes the largest reservoir of C in terrestrial ecosystems, containing 2450 Pg total C, 1500 Pg as soil organic carbon (SOC) and 950 Pg as soil inorganic carbon (SIC) (Lal 2004a; Houghton 2007; Morgan et al. 2010) in the top 1 meter of soil with an additional ~894 Pg total C found between 1 and 3 meters depth (Chapter 2, this volume). There is a strong link between atmospheric CO2 and SOC that is facilitated by C transfer through the terrestrial biotic pool (Lal 2004b). Approximately 60 Pg of atmospheric C is transferred to terrestrial ecosystems annually through the process of photosynthesis and an equivalent amount returned back to the atmosphere through soil and root respiration. (Lal 2004b; Morgan et al. 2010). Currently atmospheric carbon dioxide content is increasing at the rate of ~4.1 Pg C yr–1 (IPCC 2007) and a small fraction is estimated to come directly from agricultural activity (Lal 2007; Morgan et al. 2010). Full accounting of C emissions and sequestration to obtain net C flux budgets for agriculture indicate that agricultural land can function as a net source or sink of C (McLauchlan 2006), depending on land use and management.
Adoption of land-management strategies that foster carbon (C) sequestration in agricultural soils will be important over the next several decades as new mitigation strategies and technologies are developed to reduce C emissions (Smith 2004). Agricultural land-management options currently recommended to foster C sequestration nearly always include some reduction in tillage intensity and implementation of integrated, multifunctional cropping rotations that include forage legumes, small grains, and organic amendments from animal manure or compost, supporting the production of primary commodity crops (e.g., corn, soybean, wheat, rice, and cotton).
Recent volatility in supplies and prices of natural gas and synthetic nitrogen (N) fertilizer suggests a need to develop and refine alternative strategies for supplying N to corn. In this study, conducted in north-eastern Iowa, we examined the use of red clover and alfalfa green manures as means of supplying N to a succeeding corn crop. Red clover intercropped with oat produced significantly more biomass and contained more N than alfalfa intercropped with oat. Tilling green manures in the fall or delaying tillage until the following spring did not have a consistent effect on green manure N content. Without N fertilizer, corn grain yield following oat–red clover and oat–alfalfa was 25–63% greater than following oat grown alone, but at the highest fertilizer rate (202 kg N ha−1), there was no difference in corn yield between oat–legume and oat-alone treatments. These patterns support the premise that legume green manure effects on corn yield were N-related. Red clover green manure had an N fertilizer replacement value for corn of 87–184 kg N ha−1; alfalfa supplied corn with the equivalent of 70–121 kg N ha−1. At a fossil energy cost for N fertilizer of 57 MJ kg−1 N, reducing synthetic N fertilizer applications to corn by 70–184 kg N ha−1 would represent a fossil fuel savings of 3990–10,488 MJ ha−1, equivalent to the energy content of 104–274 m3 of natural gas. These types of savings are likely to become increasingly important as fossil energy supplies become scarcer and fertilizer prices rise.
Email your librarian or administrator to recommend adding this to your organisation's collection.