Agricultural intensification to increase food, feed, and fibre production has also resulted in environmental degradation, including poorer soil quality and high emissions of greenhouse gases (GHGs) like nitrous oxide (N2O). Intercropping, an agroecosystem management practice where more than one crop is planted on the same plot of land at the same time, promotes the complementary use of soil nutrients, and may improve soil quality and increase the retention of inorganic nitrogen (N) in the soil, thereby reducing N2O emissions. An experiment was conducted in Balcarce, Argentina to determine the impact of intercropping maize (Zea mays L.) and soybean (Glycine max (L.) Merr.), (either 1:2 or 2:3 rows of maize to soybean) on soil quality and soil N transformations after six cropping seasons. It was found that intercropping significantly improved soil quality over a six year period, as indicated by the soil organic carbon (SOC), soil total nitrogen (TN), soil light fraction organic matter (LF), and soil microbial biomass carbon (SMB-C). However, the soil quality also significantly improved in the sole crops over this time, and in 2012, only SMB-C was significantly (p<0.05) greater in the 2:3 intercrop than in the sole crops. Intercropping resulted in higher rates of gross nitrogen (N) mineralization than the sole crops, and the 2:3 intercrop resulted in higher rates of gross N immobilization than in the other treatments. However, the high rate of gross N mineralization resulted in a low relative NH4+ immobilization in both intercrops, signifying a lower potential for reducing soil NH4+ concentrations than in the sole crop treatments. Net N immobilization occurred in all treatment plots, which was desired at the end of the fallow period to reduce N losses from the soil. The 2:3 intercrop appeared to perform better than the 1:2 intercrop. However, further research needs to be conducted to determine the seasonal variations in N mineralization and immobilization, and to further examine the intercrop spatial arrangements to increase crop residue yield.

If upland rice production is to be sustained on sloping land, soil erosion and fertility decline must be addressed. Where soil profiles are deep, hedgerows of Gliricidia sepium and Cassia spectabilis, planted on the contour, reduce soil erosion by promoting terrace formation and overcome fertility depletion by providing nutrient rich biomass. G. sepium and C. spectabilis established by seed survived better than by cuttings. Although increased hedgerow biomass was initially obtained when both species were intercropped, intense competition was observed in established hedgerows. Consequently, mixing both species at high planting density is not recommended as C. spectabilis, a non-fixing legume, may deplete soil-N reserves. In acid soils, biomass production of G. sepium was significantly increased when lime (6 t/ha) was applied. On 18 to 30% slopes, upland rice and maize production improved along fertility and moisture gradients. Rice yields were increased when biomass of G. sepium was incorporated into the soil, up to an optimum level equivalent to 40 kg N/ha. Mulching C. spectabilis increased maize productivity during the drought prone second season. Competition was observed at the hedgerow-crop interface particularly at the upper one as a result of terracing. Although green manuring increased crop yield, broadleaf weeds, seedling maggot, stemborer and blast also increased. Strategies to manage hedgerow biomass that minimize these problems need to be developed.

Intercropping systems offer potential benefits relative to monocultures of increased crop yields and improved pest control through physical, chemical, or behavioural interference and the enhancement of natural enemy populations, prompting increased predation and parasitism. Intercrops of canola (Brassica napus L.) and wheat (Triticum aestivum L.) in various proportions were investigated at three sites in Alberta, Canada, in 2005 and 2006, to determine effects on 1) agronomic parameters, including crop grain and biomass yields, crop quality (canola oil and canola and wheat protein), lodging, soil microbial communities, and wheat leaf diseases; 2) pest insects, including flea beetle (Phyllotreta spp.) (Coleoptera: Chrysomelidae) damage to seedling canola and root maggot (Delia spp.) (Diptera: Anthomyiidae) adult collection numbers, egg populations, and canola taproot damage; and 3) beneficial insects, including ground beetles (Coleoptera: Carabidae) and the predator-parasitoid Aleochara bilineata Gyllenhal (Coleoptera: Staphylinidae). Crop yields were similar in intercrops and monocultures, and benefits of intercropping were observed in enhanced crop quality characteristics in some site-years. Neither soil microorganisms nor wheat leaf diseases generally responded to intercropping regimes. Intercropping did not reduce flea beetle damage to canola seedlings. Flea beetle damage was greatest at the first true-leaf stage of canola development. Although a thiamethoxam seed treatment reduced flea beetle herbivory, untreated plots generally did not sustain greater than 20% damage, suggesting that seed treatments were usually unnecessary. Adult Delia did not respond to intercropping canola with wheat, but egg populations were lower in intercrops on a land area basis. Canola taproot damage was as much as 13% reduced in intercrops compared to monocultures. Carabid beetles appeared to respond to qualities of the intercrops and monocultures, such as ground cover, rather than to the level of vegetational diversity itself, but carabid diversity was enhanced in diverse intercrops compared to canola monocultures in one site-year. Aleochara bilineata adult populations and parasitism rates were favoured in canola monocultures, but a temporal shift in A. bilineata adult collection numbers suggests reduced preference for canola monocultures in early summer. Benefits of canola-wheat intercrops identified in this study do not appear sufficient to recommend these cropping systems for widespread adoption in western Canada. / Plant Science

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2005. / Härtill 4 uppsatser.

Thesis (Ph. D.)--Oregon State University, 1997. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 75-81). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2004. / Typescript. Vita. Includes bibliographical references (leaves 75-81). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2000. / Typescript. Vita. Includes bibliographical references (leaves 230-254). Also available on the Internet.

Thesis (doctoral)--Swedish University of Agricultural Sciences, 2000. / Includes bibliographical references.

Thesis (M.S.) University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (May 20, 2007) Vita. Includes bibliographical references.