Tilled plots

The interaction of all these factors makes it difficult to predict an overall effect of conservation tillage on the potential leaching of a pesticide compared to that in a conventionally tilled field. However, it was found that a prolonged rain immediately after appHcation resulted in short-term levels of pesticide in groundwater to be greater under no-tiU than under conventional till plots, which suggested that preferential transport in no-tiU had occurred... 

In addition to morningglory, similar trends were observed for cockle-bur (Xanthium pensylvanicum Wallr.). Higher cocklebur populations were observed in tilled plots than in non-tilled plots (data not shown). 

No deleterious effects of either the wheat mulch or tillage were observed on soybeans (Table V) or corn (data not presented). In general, crop growth was better in mulched or no-till plots. Enhanced soil moisture in the mulched treatments and reduced morningglory densities in the non-tilled treatments may have contributed to improved crop growth. 

In contrast, Blevins et al. (1990) found that while there was a third as much runoff volume from no-till plots over a 2-year period as compared to conventional-tillage plots, atrazine loss in runoff was about the same in both systems (<1% of applied atrazine). Most of the loss occurred between application and com canopy closure. Also, Fermanich et al. (1996) found that although cumulative drainage under no-till plots was always greater than under moldboard-plow plots, there was no consistent effect of tillage on atrazine loading. 

Foy, C.L., J.S. Wilson, S. Mostaghimi, and R.W. Young (1989). Runoff losses of two triazine herbicides and metolachlor from conventional and no-till plots as influenced by sludge. Pestic. Terrest. Aquatic Environ. Proc., May 11-12, pp. 383-396. 

Intensive research on no-till com production was conducted in Virginia after a test in 1960 on orchardgrass sod was highly successful (Moody et al., 1961). Orchardgrass killed with 4.4kg/ha atrazine was compared with tilled plots. Stover yields were 33% higher on the unfilled plots with atrazine. 

Fermanich, KJ. and T.C. Daniel (1991). Pesticide mobility and persistence in mycrolysimeter soil columns from a tilled and no-tilled plot. J. Environ. Qua ., 20 195-202. 

Comparisons of stubble mulch with complete chemical fallow systems of farming have usually given results that favor the former system. For example. Black and Power (1965) reported that wheat yields on stubble-mulched soils were higher than where spray was used. Furthermore, neither chemical fallow nor combinations of chemical and mechanically-tilled plots resulted in more moisture conservation than with conventional stubble mulch. Wind erodibility was, however, less with complete chemical fallow soils, doubtless because of complete absence of tillage. 

Rainfall for April-August was 7.8 and 22.6 cm below normal (57 cm) in 1992 and 1993, respectively. June of 1993 was so dry that plots were irrigated (2.5 cm) with an overhead sprinkler system to prevent the loss of the experiment. Although locations of treatment plots each year were chosen at random there may have been differences due to cover crop carry-over from 1 year to the next since the experiments for the 2 years were carried out in the same field. For example the soil nitrate-N levels for clover no-till plots in 1993 (mean values from 22 to 50 xg/g soil) were considerably higher than for the 1992 plots (mean values from 5 to 9.5 p,g/g soil Blum et al. 1997). 

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 ... 

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. 

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