Ontario - Canada Logos
SWEEP Banner

SWEEP Report #56

Yield Reduction Effects of Crop Residues
in Conservation Tillage

Researchers: 
R.P. Voroney, B.J. Farquharson, K.J. Janovicek, E.G. Beauchamp and T.J. Vyn, University of Guelph, Guelph, Ont. and M.C. Fortin, Agriculture Canada, Ottawa, Ont.

Executive Summary

Evaluation Summary (Tech. Transfer Report Summaries)

View / Download Final Report [1026 KB pdf]

 

 

List By Number | List By Sub-Program

Completed: July, 1992

Key Words:

crop residues, conservation tillage, canola, corn, red clover, rye, soybeans, winter wheat, crop rotation, soil moisture, soil temperature, residue cover, phenolic acids, volatile fatty acids, phytotoxin, calcium nitrate, zero-till, yield

Executive Summary

Field Studies

The presence of crop residues on the soil surface in conservation tillage systems affected soil water content and temperature, and plant growth. When the spring season was dry, residues retarded evaporation resulting in soil temperatures cooler in comparison to a conventional tillage system. However, the extra water retained in the soil also promoted plant growth. During a wet season, plants appeared pale and growth was stunted due to cooler soil temperatures and wetter soils. Nevertheless, soil temperature and moisture measurements could not totally explain the reduction observed in corn plant development in the presence of specific plant residues, particularly residues of red clover and canola.

Phenolic acids (PCs) and volatile fatty acids (VFAs) generally were not found in concentrations considered to be phytotoxic in field soil samples. Field sampling in the spring showed the presence of PCs which tended to decrease in concentration from May to June. However, within 48 hours after a 40 mm rainfall event in late June, PCs were detected in plots with residue cover. The presence of VFAs was detected only once during the three years of study in the field. This was after a shower in early June from a plot receiving rye residues (4 t/ha).

The addition of calcium nitrate to soil amended with crop residues significantly reduced accumulation of VFAs in a laboratory study. However, under field conditions the addition of calcium nitrate with the seed did not overcome the yield reduction effects of rye residues.

Laboratory Studies

The production of VFAs is dependent on the nature of the crop residue, soil water content and temperature. Green, readily decomposable residues such as legumes had the greatest potential for the accumulation of VFAs when soil temperatures were high (15-25 C) and soil water potential was above field capacity. The potential for VFA production decreased as the plant materials matured to harvest stage and underwent weathering.

There was little difference in the accumulation of VFAs under soil moisture conditions ranging from field capacity to saturation. Phytotoxic concentrations could be produced in the laboratory within 48 hours of incubation, a period which could be expected in the field.

The accumulation of VFAs was much greater at high temperatures (25 C) than at low temperatures (4 C). During incubations there was a lag period of about 2 days followed by a rapid increase in VFA accumulation to a maximum at about 14 days. This was followed by a rapid decrease in soil VFA concentration indicating that these compounds were readily utilized by soil microorganisms. A second but much smaller peak was observed on day 28, especially for rye and soybean residues. Under low temperatures (4 C), VFA accumulations were small but steady over the entire incubation period. Total phenolic concentrations were never as high as those found for VFAs. This may be because VFAs are a by-product of anaerobic decomposition whereas PCs are released as the residue undergoes decomposition.

Bioassays using corn and winter wheat were performed to assess phytotoxic affects. Selected VFAs and PCs inhibited germination and early growth of corn, although not all hybrids were affected equally. Phytotoxicity increased with decreasing solution pH. Combinations of the phenolic acids appeared to affect corn radicle growth in a non-additive manner.

The winter wheat bioassay showed that VFAs were more inhibitory to plant growth than PCs. Acetic acid was inhibitory to both radicle and coleoptile growth, irrespective of crop variety or VFA concentration tested. Propionic and butyric acid also inhibited plant growth but to a lesser extent than acetic acid. Vanillic acid was inhibitory to germination and early seedling growth whereas p-hydroxybenzoic acid and p-coumaric acid stimulated early seedling growth.

In conclusion, the field research indicates that phytotoxins are produced from decomposing crop residues which can significantly reduce plant growth. However, the nature of these phytotoxic compounds is not clear. VFAs and PCs accumulated in the soil to phytotoxic concentrations during the decomposition of particular crop residues in laboratory studies. However, these compounds were not detected in field studies. Future research should consider the dynamics of both the production and utilization of phytotoxin compounds during decomposition of crop residues. In addition, there is a need to examine other potential phytotoxins, such as the volatile C6 through C9 organic compounds.

 

Evaluation Summary

(From Technology Transfer Report Summaries - A. Hayes, L. Cruickshank, Co-Chairs)
The aim of this study was:
  1. to evaluate surface placement of coarsely-chopped overwintered corn and fresh rye plant residues for phytotoxin production using corn as the test crop,
  2. to evaluate the effects of various crop residues and residue placement options on zero-till corn performance,
  3. to evaluate calcium nitrate amendments to seed row using corn as the test crop
  4. to determine the soil environmental factors controlling the production and accumulation of phytotoxins,
  5. to compare the production of volatile fatty acids and phenolic compounds from weathered versus fresh manure residues under saturated conditions and 15 C,
  6. to determine the effects of volatile fatty acids and phenolic acids on early corn radicle growth,
  7. to determine the effects of volatile fatty acids and phenolic acids on winter wheat bioassays.
The study concluded that the presence of crop residues on the soil surface in conservation tillage systems affected soil water content and temperature, and plant growth, however measurements of the soil moisture and temperature could not totally explain the reduction in corn plant development particularly under residues from red clover and canola.

The phenolic acids (PCs) and volatile fatty acids (VFAs) were not found in concentrations considered phytotoxic in field soil samples, however they were detected in some plots after certain June rain events.

Calcium nitrate reduced accumulation of VFAs when added to soil in the laboratory study, however when added with the seed under field conditions the yield reduction effect of rye residue was not overcome.

In the laboratory VFA production was found to be greatest under green readily decomposable residue such as legumes, under high soil temperatures (15-25 C), and soil water potential above field capacity. The potential for VFA production decreases as the plant materials matured to harvest stage and underwent weathering. Phytotoxic concentrations could be produced within 48 hours of incubation, and increased to a maximum at about 14 days.

  • From the corn bioassay it was determined that some VFAs and PCs had a phytotoxic affect, although not all hybrids were affected equally.
  • From the winter wheat bioassay it was determined that the VFAs were more phytotoxic than the PCs.

Comments:

This study set out to answer some of the questions farmers have been asking about phytotoxicity of crop residues. While the acids were found at toxic levels in the laboratory, they were not detected in the field.

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

(B) This study considered certain VFAs and PCs, whereas other compounds such as the volatile C6 through C9 organic compounds could be examined. Future research should consider the dynamics of both the production and utilization of phytotoxin compounds during decomposition of crop residues.

 

 

 

List By Number | List By Sub-Program | LSP Report List
SWEEP Home

 

Created: 05-28-1996
Last Revised: Thursday, May 19, 2011 04:09:49 PM