Potato Cropping Systems to Manage Soilborne Disease

Long-term cropping systems research is expensive, difficult to manage, and therefore rare, especially for vegetable crops. So when results are published for potato cropping systems, it is worthwhile taking a look. A team from Maine recently reported the results of experiment comparing four cropping systems:

• Industry standard system: Barley/Clover – Potato
• Soil Conservation system: Barley/Timothy – Timothy – Potato
• Soil Improvement system: Barley/Timothy – Timothy – Potato with yearly application of compost (20 wet tons/acre)
• Disease Reducing system: Mustard/Rapeseed – Sudangrass/Rye – Potato

All systems were managed under both natural rainfall and irrigation.

Results

Under rainfed conditions, the soil benefits of the compost provided the highest yields and percentage of large tubers.

Under irrigation, the disease reduction system out-yielded both the soil conservation and soil improvement systems. The yields in the soil improvement system did not increase under irrigation, suggesting that it was the increased water holding capacity of the soil that increased yields under rainfed conditions. With this benefit negated by irrigation, the advantage in the higher yielding environment went to the disease reduction system.

The experiment was on a sandy loam with 4.5% soil organic matter and a pH of 5.8. Russet Burbank potatoes were used. Fertilizer was applied to eliminate nutrient effects across systems. The experiment ran from 2004 to 2010.

Reduction of soilborne disease does not require an increase in soil organic matter.

Figure 1 from Larkin et al. (2021) shows the increase in soil organic matter as a result of compost in the SI system. In the disease reducing system, soil organic matter did not increase; the reduction of disease was not dependent on an increase in soil organic matter, which is good news. Neither is it related to the compost-driven increases in soil nutrient levels (Fig. 2 of the same paper, not shown). The soil improvement system, while improving many of the common soil health indicators, did not reduce the soilborne diseases important there. Soil health is not soilborne pest suppression (see article on this). Conversely, the disease reducing system did not affect any of the chosen soil health measurements, suggesting that the disease reduction may be due to changes in the composition of the soil microbial community that are difficult to measure.

Notable Points

Although there are differences between potato production in Maine and in the Columbia Basin, there are some things we can gain from this study:

• For high-yield irrigated potato production, a focus on soilborne disease control is warranted. This is also the conclusion of a survey done for the Washington Soil Health roadmap.
• Even though our green manures are grown in the late summer and fall, because of our longer growing season, they have similar biomass yields to the full-season green manure crops used in this study.
• The Maine soils started with higher organic matter levels than we have, ~4.5%. Compared to our soils, this larger pool will reduce the impact of green manures on soil organic matter levels. However, green manures still reduced soilborne diseases (stem canker, black scurf, and common scab) suggesting this benefit is not related to organic matter levels.
• The effects of cropping system changes, like the use of compost and green manures, increase over time. Do not expect much after using them once.
• Compost-driven improvements in soil health will not substitute for water in Eastern Washington as we receive much less rainfall. It could, however, be useful in Western Washington.

Long-term potato cropping systems research starting

WSU potato soil health specialist Steve Culman is now planning for a long-term trial of similar potato cropping systems at the WSU Othello research farm. Treatment variables will include green manures, compost, various rotation lengths, perennial crops, and fumigants. It all comes down to economics; can these systems be profitable? Stay tuned.

References

Halloran, J. M., Larkin, R. P., DeFauw, S. L., Olanya, O. M., & He, Z. (2013). Economic potential of compost amendment as an alternative to irrigation in Maine potato production systems.

Larkin, R. P., Griffin, T. S., Honeycutt, C. W., Olanya, O. M., & He, Z. (2021). Potato cropping system management strategy impacts soil physical, chemical, and biological properties over time. Soil and Tillage Research, 213, 105148. https://doi.org/10.1016/j.still.2021.105148

Larkin, R. P., Honeycutt, C. W., Griffin, T. S., Olanya, O. M., Halloran, J. M., & He, Z. (2011). Effects of Different Potato Cropping System Approaches and Water Management on Soilborne Diseases and Soil Microbial Communities. Phytopathology, 101(1), 58–67. https://doi.org/10.1094/PHYTO-04-10-0100

Larkin, R. P., Honeycutt, C. W., Griffin, T. S., Olanya, O. M., & He, Z. (2021). Potato Growth and Yield Characteristics under Different Cropping System Management Strategies in Northeastern U.S. Agronomy, 11(1), Article 1. https://doi.org/10.3390/agronomy11010165

Larkin, R. P., Honeycutt, C. W., Griffin, T. S., Olanya, O. M., He, Z., & Halloran, J. M. (2017). Cumulative and residual effects of different potato cropping system management strategies on soilborne diseases and soil microbial communities over time. Plant Pathology, 66(3), 437–449. https://doi.org/10.1111/ppa.12584