Sustainable Spuds Q & A

Please tell me about the sustainable potato production research you’re working on. What does it entail specifically?

Hal Collins: • Develop strategies for improvement of C sequestration and nutrient availability under irrigated potato production systems incorporating reduced tillage and organic amendments to decrease greenhouse emissions under high nitrogen fertilizer inputs, and calibrate and verify residue decomposition and C sequestration models.
• Provide guidelines of nutrient cycling and suppression of soil borne pathogens under cropping systems incorporating cover crops or by-products from agricultural-based energy production that producers can use to augment/supplement fertilizer and pesticide use without affecting product quality or causing long-term degradation of soils.
• Provide growers with techniques that improve their capacity to predict and manage soil resources when under reduced tillage and organic amendments to soil productivity.

How long have you been working on the research?

Collins: 8 years

What have the findings been so far?

Collins: Reduced tillage in Potato Production systems: Adoption of conservation tillage in irrigated potato cropping systems has been limited due to a perception of poor crop stands, increase in disease and pest problems and the high cost to replace equipment. Intensive agriculture and increased N-fertilizer use have also contributed to elevated emissions of the greenhouse gases, CO2, CH4, and N2O. We developed reduced tillage protocols using contemporary equipment and examined the impact of reduced tillage on potato yield, soil microbial populations, soil organic matter dynamics, and trace gas fluxes. Crop yields and soil microbial characteristics were not changed by using reduced tillage. We showed minor losses (0.4%) of the applied fertilizer as N2O from irrigated potato fields. We attributed this low value to applying split applications of fertilizer through the irrigation system during the growing season. The global warming potential (GWP) contribution from corn and potato fields were 7843, and 6028 kg CO2-equivalents ha-1, respectively. These trace gas flux data will refine estimates of trace gas emissions from irrigated croplands. The new tillage strategy reduced the total number of passes across the field from nine to six and soil disturbance operations from seven to four, including harvest, compared to conventional tilled potato treatments. For sweet corn, soil disturbance field operations were reduced 100%. Growers can account for 1 to 7% of the N-fertilizer applied as a gaseous N2O loss depending on the form of fertilizer applied. Adoption of reduced tillage in specialty crop production is increasing.

Mustard Cover Crops: Because of the high cost of using synthetic soil fumigants and potential loss of soil microbial functions potato growers are increasingly interested in growing mustard cover crops containing high glucosinolate concentrations as green manures to reduce soil pathogens and offset fertilizer and chemical costs. Glucosinolates in mustard residues degrade to isothiocyanates and are similar to the active ingredient of commercial soil fumigants. We demonstrated that fumigation significantly reduced selected soil pathogens and nematodes, but only minimally affected microbial functions. Fumigation significantly reduced populations of Pythium spp. by 97%, Fusarium spp. by 84%, and Verticillium dahliae by 56% compared to the mustard cover crop. We showed that although the cover crop did not reduce the presence of plant pathogens the incidence of disease caused by these soil pathogens was not expressed and exhibited no reduction in tuber yield. Reductions in the incidence of disease where cover crops were used were attributed to the 23% increase in soil microbial biomass and mechanisms such as microbial competitive exclusion. In a related study, we showed that the mustard cover crop recovered 34 to 51% of applied fertilizer with 29 % of the N in the cover crop available to the following potato crop. This research reduced concerns of potato growers that fumigation adversely affected soil microbial populations and the mineralization of soil N. Growers incorporating mustard cover crops in rotation can offset fumigation costs and save up to $130/ha. The planting of mustard cover crops by potato growers has increased from 800 to 8,000 ha in Washington State. Growers can also budget 30 to 44 kg N ha-1 present in the mustard cover crop as a source of N to the subsequent potato crop and save $14-20 ha-1 at current fertilizer costs. We have also shown reductions in weed populations.

What does the research mean for the future of potato production?

Collins: Decreased costs of production and greater ability to maintain yields and quality.