No-till reference plots

Mean soil moisture values in 1992, based on 4 sampling times, were 0.109 0.005 g water/g soil for the no-till reference plots and ranged from 0.136 0.003 g... 

Since for the 1992 and 1993 no-till field studies (Blum et al. 1997) both root and shoot residues of rye, wheat, crimson clover, and subterranean clover were present in each no-till plot, the role of shoot or root residues alone on weed seedling emergence could not be determined. Thus for the 1996 and 1997 field studies, sets of no-till plots with only root residue (i.e., shoots removed), only shoot residue (i.e., cut shoots from root plots placed on no-till reference plots), and shoot (uncut and cut but left in place) and root residues were included in the experimental design (Blum et al. 2002). However, to make the 1996 and 1997 field studies more manageable, only one cover crop, wheat, was utilized. 

Fig. 3.12 The number of pigweed seedlings in cover crop and reference plots for the 1993 experimental period in no-till Cecil A soil. Glyphosate desiccation of cover crops occurred on April 29 (a) and May 10 (b). Where C equals crimson, S equals subterranean and reference equals no-cover crop plots. Figures reproduced from Blum et al. (1997). Henry A Wallace Institute for Alternative Agriculture Inc, figures used with permission of Cambridge University Press...

Soil compaction determined for no-till plots on July 5 in 1993 with a soil penetrometer found that only reference plots (28 2 mm penetration) and rye plots (40 2 mm penetration) were significantly different (Blum et al. 1997). Dramatic differences would not be expected since these were all one season no-till plots. No significant differences were observed for the incorporated cover crop plots. Minimum and maximum penetration for these plots ranged from 40 3 (wheat) to 53 4 (crimson clover) mm. Soil pH, determined approximately biweekly for the experimental period, was not modified by the presence of the various cover crops. Mean pH values ranged from 4.8 to 5.2. 

Soil nitrate-N values, however, were modified by the presence of the cover crops. In 1992 the means for soil nitrate-N determined at two points in time (May 12 and June 19) were as follows no-till plots without cover crops (reference plots) 3.25 1.11 tig/g soil, crimson clover plots 4.82 0.85 p,g/g soil, subterranean clover plots 9.44 1.58 p,g/g soil, rye plots 1.71 0.04 p,g/g soil, and wheat plots 0.80 0.16 rg/g soil (Blum et al. 1997). In 1993 (April desiccation) the means for soil nitrate-N determined at three points in time (May 31, June 14, and July 5) were as follows no-till plots without cover crops (reference plots) 18 5 p,g/g soil, crimson clover plots 34 7 p,g/g soil, subterranean clover plots 50 12 p,g/g soil, rye plots 13 3 rg/g soil, and wheat plots 22 5 p,g/g soil (Blum et al. 1997). For May desiccation these values were as follows no-till plots without cover crops (reference plots) 18 5 p.g/g soil, crimson clover plots 22 5 p,g/g soil, subterranean clover plots 50 13 p.g/g soil, rye plots 11 3 p,g/g soil, and wheat plots 14 5 p,g/g soil. The differences in nitrate-N between 1992 and 1993 were due partly to carry over ... 

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