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SWEEP Report #30

The Response of Soil Microflora and Fauna to Spring Plowing
of Zerotill and Pasture Soils

Researchers: 
P. Neave, V. Thomas, Department of Zoology, University of Guelph, Guelph, Ont.

Executive Summary

Evaluation Summary (Tech. Transfer Report Summaries)

Associated SWEEP/LSP Research

View / Download Report [596 KB pdf]

 

 

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Completed: October, 1991

Key Words:

soil microbiology, soil biology, soil quality, no-till, pasture soils, spring plowing, earthworms, nematodes, cryptozoic invertebrates, mites, springtails, bulk density, infiltration, soil temperature

Executive Summary

The purpose of this study is to use populations of soil organisms to contrast ecosystem stability in an undisturbed pasture with a zerotill winter wheat field. Soil organisms that were considered include soil microbial biomass, nematodes, earthworms, soil dwelling arthropods, cryptozoic invertebrates, and emergent arthropods. The pasture represents a more natural ecosystem as it is undisturbed agriculturally, and the zerotill field represents an actively managed agroecosystem.

Stability was measured by perturbing the populations of soil microflora and fauna by plowing and disking the soil, and measuring their time to return to, deflection from, and rate of return to, the ground state. Return time was faster and deflection from ground state was less in the zerotill agroecosystem than in the pasture system. These results suggest that agroecosystems are not unstable, as communities within the agroecosystem can recover from perturbation. Diversity, as measured by richness and evenness, was similar in pasture and zerotill soil for those populations for which it was determined.

Litter decomposition rate (LDR) was measured using litterbags. LDR was faster in the zerotill plowed system compared to pasture plowed, possibly because of the more rapid return of macro-invertebrates in the plowed soil. Differences in soil microbial biomass do not appear to account for differences in LDR.

Saturated hydraulic conductivity (SHC) and dry bulk density (DBD) were used to measure pore continuity. In the zerotill system, SHC and DBD were significantly higher in the unplowed soil indicating that pore continuity is much higher in unplowed soil. In the pasture system, plowed soil had a higher SHC and a similar DBD to that of unplowed soil indicating that pore continuity is higher in plowed soil, possibly because of the destruction of roots previously plugging the pores of unplowed soil.

Water infiltration rate was found to be correlated with the number of earthworms in pasture and zerotill unplowed and plowed soils. This illustrates the importance of bioporosity in these soils.

The recommendation to plow zerotill soils every 4-5 years is put into question by this study. The soil quality indicators of earthworm number, water infiltration rate and pore continuity indicate that plowing zerotill soil may not be beneficial. Chisel plowing or ridge tillage might be acceptable intermediates.

Number of mites and richness and abundance of soil dwelling arthropods were modelled against various environmental parameters. Cropping system (pasture or zerotill), depth, and organic matter content appear to strongly influence the distribution of soil dwelling arthropods. Tillage (yes or no), water content and wet bulk density were not as important determinants. Number of mites did vary with depth over the season, numbers increasing with depth in the plowed soil, and decreasing with depth in the unplowed soil. Mites returned to the upper levels of plowed soil when temperatures and vegetational growth returned to similar levels to that of the unplowed soil.

 

Evaluation Summary

(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank, Co-Chairs)

A one year study using soil organisms to contrast the agro-ecosystem stability in an undisturbed pasture with a zero-till winter wheat field in plowed and unplowed plots. Four treatments were studied: a pasture field and a zerotill field; each of these were split in half, one side was moldboard plowed and the other was left unplowed. Numerous parameters were evaluated and results are as follows:

  1. Abundance of nematodes - The number of nematodes was initially higher in zero-till than in pasture but towards the end of the growing season nematode numbers were higher in pasture soil. Number of nematodes correlated with saturated hydraulic conductivity in pasture soil, therefore in this soil, pore size might be limiting the activity of nematodes.

  2. Earthworms - The number of earthworms in all sample plots were at a maximum at the end of the season (November). At the end of the season the number of earthworms in unplowed pasture soil was more than double that in unplowed zero-till soil. Pasture soil may take several years for populations to return. Earthworm populations do not appear to recover fully from plowing even after six months.

  3. Cryptozoic invertebrates - The abundance of invertebrates was generally low in the spring, high in the summer and low again in late fall. There was no significant difference among plots. Slugs were similar in numbers in pasture and zero-till plots. The highest numbers were in plowed pasture and unplowed zero-till soils at the end of the sampling period. Similar trends were found for sowbugs except the number of sowbugs were higher in unplowed pasture than in plowed soil in mid-summer.

  4. Mites and springtails - The occurrence of mites and springtails were similar in all plots. The average number of animals in unplowed pasture and zero-till was higher in the surface soil (0-5 cm). In plowed pasture and zero-till the numbers were found at greater depths (5-15 cm). Tillage alone doesn't influence distribution of mites. Changes in the soil after tillage has a greater influence.

  5. Soil Biomass - Soil biomass was almost always higher in pasture soil regardless of whether it was plowed or unplowed. Soil biomass C:P ratios were generally higher in pasture soil than in zero-till.

  6. Litter decomposition rate (LDR) - The LDR was higher in zero-till plowed soil than in pasture plowed soil 39 and 69 days after plowing.

  7. Dry Bulk Density (DBD) - DBD was similar in unplowed and plowed pasture soils and was significantly higher in zero-till unplowed versus plowed soil.

  8. Infiltration rate - Infiltration rate was higher in unplowed pasture and zero-till soils than in plowed soils. The average infiltration rate increased with increasing earthworm numbers and earthworm mass. The higher infiltration rate in unplowed soils at this site could be due to biopores transmitting more water than macropores.

  9. Soil temperature in the plowed zero-till and plowed pasture soils had higher temperatures than unplowed soils. This difference disappeared by late summer.

  10. Water content - There was no significant difference in water content amongst the plots.

  11. Stability - Return times of population parameters were faster in zero-till soil. The zero-till community was more stable (by definition) than the pasture community.

  12. Diversity as measured by richness (number of species per catch) and evenness were the same in zero-till and pasture soils.

Some conclusions from the report are:

  1. Plowing reduces earthworm populations (even after six months) and reduces the water infiltration rate.

  2. The study shows a long time is required for zero-till soil to "peak" biologically.

  3. The zero-till community is more stable than the pasture community.

Comments:

This is a good report (although very technical) with some interesting trends showing up. From this report it would seem that we should not be recommending to plow zero-till soil 4-5 years into the system to mix the soil. This would harm earthworm numbers and infiltration rates. It is important to note that our soils tend to be very stable ecosystems and return times for organisms are relatively quick after cultivation (except for earthworms).

Associated SWEEP/LSP Research:

  • SWEEP Report #47 - Effect of Woodlot Borders and Crop Residue on the Distribution of Invertebrates in Agroecosystems

  • SWEEP Report #37 - Effects of Tillage on the Quality and Quantity of Surface and Subsurface Drainage Water: Uplands

  • LSP 7016 - Response of the Soil Microflora and Fauna to Spring Plowing of Zerotill and Pasture Soils

Future Research: ( ) indicates reviewers suggestion for priority, A - high, C - low.

(A) Future research into soil life should differentiate, where possible, amongst soil organisms which are beneficial to agriculture and those that are not. It would be interesting to see differences amongst zero-till, minimum till and moldboard plow systems examined.

 

 

 

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Created: 05-28-1996
Last Revised: Thursday, May 19, 2011 02:44:49 PM