Tillage systems

Saprophytic, dark pigmented fungi such as Alternaria spp. can infect a wide range of plant species, especially tissues that are exposed to other biotic or abiotic stressors and older and senescing plant tissues. Also, wet weather conditions favour attack by Alternaria spp. Inoculum of Alternaria and potentially production of altemariol is further enhanced when cereal straw and stubble is left on the soil surface and not sufficiently incorporated into the soil after harvest (direct seeding and minimum tillage systems). 

Home DJ, Ross CW, Hughes KA (1992) Ten years of a maize/oats rotation under three tillage systems on a silt loam in New Zealand. I. A comparison of some soil properties. Soil Till Res 22 131-143... 

Hemanz JL, Lopez R, Navarrete L, Sanchez-Giron V (2002) Long-term effects of tillage systems and rotations on soil structural stability and organic carbon stratification in semiarid central Spain. Soil Tillage Res 66 129-141... 

Queslati O, Ben-Hammouda M, Ghorbal MH, Guezzah M, Kremer RJ (2005) Barley autotoxicity as influenced by varietal and seasonal variation. J Agron Crop Sci 191 249-254 Raimbault BA, Vyn TJ, Tollenaar M (1990) Com response to rye cover crop management and spring tillage systems. Agron J 82 1088-1093... 

Rizvi SJH, Mishra GP, Rizvi V (1989) AUelopathic effects of nicotine on maize I. Its possible importance in crop rotation. Plant Soil 116 289-291 Roshchina VV (2001) Molecular-cellular mechanisms in pollen allelopathy. Allelopathy J 8 11-28 Roth CM, Shroyer JP, Paulsen GM (2000) Allelopathy of sorghum on wheat under several tillage systems. Agron J 92 855-860... 

In the field, atrazlne has been found to have a half-life of <1 month, but the half-life is affected by the tillage system (44-46), the agricultural soil ammendments and soil pH (45-48), and soil organic matter (49). In another study, atrazine and hydroxyatrazlne have been found to persist into the following growing season (50). 

In the direct drilling (no-till seeding) practice in the united Kingdom/ straw residues from the preceding crop are usually burnt because poor crop establishment and yields can result/ particularly on heavy soils in wet years (10). Similar problems can occur in the conservation tillage systems oF the Pacific Northwest (L.F. Elliott and H.-H. Cheng/ this volume). 

Conservation agroecosystems developed in the Great Plains of the U.S. to control soil erosion are characterized by the presence of varying quantities of plant residues on the soil surface. This residue mulch protects the soil from the erosive forces of wind and water, resulting in improved stream water quality and soil conservation. Conservation tillage systems also help maintain soil productivity and reduce energy requirements of crop production (15). However, crop yield reduction has been observed with conservation wheat production in some areas of the U.S. (16-18) and with rice culture in the Far East (, 20). 

Allelopathic problems have been especially troublesome with conservation tillage systems (6.7.9). An example is the reduced growth of winter wheat when it is direct-drilled into stubble (Figure 1). In the heavy residues (left), the plants grew poorly. 

Developing no-tillage systems without chemicals the best of both worlds ... 

Zanin, G., Otto, S., Riello, L. and Borin, M. 1997. Ecological interpretation of weed flora dynamics under different tillage systems. Agriculture Ecosystems and Environment 66 177-188. 

Figure 16.4. SFR concentration of SOM in the 53-20-, 20-2- and <2-pm-sized organo-mineral complexes from a 0- to 25-mm layer of an acrisol under conventional and no-tillage systems. Reprinted from Bayer et al. (2002b).

Figure 16.37. Typical examples of fluorescence spectra of humic acids from Brazilian soil (Hapludox) under different tillage systems. The samples were prepared in aqueous solutions (20 mg liter-1, pH 8). (a) Fluorescence emission (Xexc = 240nm). (b) Fluorescence synchronous-scan excitation spectra (AX = 55 nm). (c) Fluorescence excitation spectra (Xem = 517 nm). (d) Fluorescence emission spectra (Xoxc = 465 nm).

Gonzalez-Perez, M., Martin-Neto, L., Saab, S. C., Novotny, E. H., Milori, D. M. B. R, Bagnato, V. S., Colnago, L. A., Melo, W. J., and Knicker, H. (2004). Characterization of humic acids from a Brazilian Oxisol under different tillage systems by EPR, 13C-NMR, FTIR and fluorescence spectroscopy. Geoderma 118(3—4), 181-190. 

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