Yields and other benefits are there under conservation potato production practices; the challenge is to reduce the cost of compost.
Conventional potato production appears ultimately to produce the highest net return per acre. But you have to weigh that against “conservation” potato production practices that not only grow potatoes, but also do more to improve overall soil quality and health. What is that worth to a producer?
That conclusion comes following a 12-year Agriculture and Agri-Food Canada (AAFC) field study comparing conventional irrigated potato production practices and conservation practices that included no till, longer rotations and the inclusion of compost in the crop fertility program.
“On the straight economics side of things, conventional production practices produced the higher net return compared to the conservation practices,” says Frank Larney, a research scientist with AAFC in Lethbridge, Alta. “And the main difference in the return per acre essentially involved the cost of producing and applying compost.
“This study didn’t figure in the value of improved soil quality and health, but we believe it does have a value. While the dollars and cents point toward conventional practices, what is improved soil quality worth? That needs to be considered.”
The actual fieldwork over the dozen years of the study was conducted between 2000 and 2011 on research plots at Vauxhall, northeast of Lethbridge. But in the years following, the data collected has been analyzed, and more than 18 research papers have been written and published. Just in the past year, Larney and colleagues published a peer-reviewed paper on the research project in the American Journal of Potato Research. While in another issue of the same journal, lead economist Mohammad Khakbazan and colleagues published another paper on the project economics.
Neither, as might be expected, make for light bedtime reading, but both make the point in some detail: if you factor in a value for soil quality and health, conservation practices can be very productive.
So what potato production systems were compared? Conventional potato production under irrigation “has relied on high levels of soil disturbance in fall and spring, e.g. moldboard plowing, chisel-plowing or double-disking (which can render the soil surface prone to wind erosion) and hilling in the early growing season for weed control,” says Larney in his paper.
Throw fertility and water on and you can produce a crop; but ultimately you run the risk of a nutrient depleted soil, low organic matter, soil compaction, risk of crusting and increased risk of erosion.
“The soil loses a number of quality factors and it’s not necessarily something you can fertilize your way out of,” says Larney.
On the conservation side, Larney applied four specific management practices that included: zero or reduced tillage where possible in rotations; fall-seeded cover crops; composted cattle manure as a substitute for inorganic fertilizer; and solid-seeded narrow-row dry bean production (in rotation).
Under both treatments, shorter and longer crop rotations were used, including three, four, five and six year rotations. Crops used in rotation included potatoes, along with sugar beet, dry bean and soft white spring wheat. Timothy and oats were included in the six-year crop rotation.
The study looked at two three-year crop rotations with both conventional and conservation practices with a crop sequence of potato-dry bean-wheat. There were also two four-year rotations with conventional and conservation plots with a crop sequence of potato-wheat -sugar beet-dry bean.
The five- and six-year rotations applied to conservation production practices only with a potato-wheat-sugar beet-wheat-dry bean sequence. The oats and timothy were only added to the six-year rotation following along after potatoes.
On the conservation production plots, composted feedlot manure was applied at the rate of 28 tonnes per hectare (about 11.3 tonnes per acre) on the shorter three-year rotations. It was applied at 42 tonnes per hectare (about 17 tonnes per acre) on the longer four-, five- and six-year rotations. Compost was fall-applied six months before potatoes appeared in rotation.
So what did the study show? There was yield variability with both systems over the 12 years largely due to lower yields in some very wet growing seasons. But overall, the conservation production practices kept pace and, in most cases, surpassed the conventional production rotations in terms of yield and potato quality.
“Our results showed that a five-year conservation rotation out-performed the three-year conventional rotation by 18 per cent for marketable yield,” says the Larney report. “We believe that a three-year conventional rotation (potato-dry bean-wheat) would represent a risk to growers in terms of lower yield.”
If you are committed to conventional production practices “simply lengthening the conventional rotation to four years” could increase yields by 10 per cent. And another option to consider, says the paper “would be to adopt a three-year conservation rotation over a three-year conventional rotation which would significantly increase yield by 10 per cent”.
The study showed the overall top performer yield-wise was the five-year rotation with conservation production practices.
Other benefits of the conservation production practices, detailed in the report, included about a 33 per cent reduction in added nitrogen fertilizer, improved aspects of potato quality (always important to processors), improved dry-bean performance in years after potatoes, improved weed control, more beneficial insects and improved soil quality.
However, what takes some of the sparkle off the benefits of conservation production practices is the cost of compost. For this study, the top cost of producing and applying feedlot compost was set at $28 per tonne. If they just factored in the actual cost of compost itself at $15 per tonne (no application cost) then the economics show the overall net return of the five-year conservation rotation closely compared with the net return of a four-year conventional rotation (about $2,044 per hectare or about $830 per acre).
“Actually, even using a compost priced at $15 per tonne, the total cost of potato in four-year conventional rotation was still lower than total cost for potato in five-year conservation rotation,” says Khakbazan. “However, at $15 per tonne for compost, the net returns of potato in four-year conventional and five-year conservation become equal because the higher potato yield achieved in five-year conservation rotation compared to the potato yield in four-year conventional rotation.”
But just looking at the dollars, the four-year conventional practices crop rotation produced the best return per acre.
“Potato growers will likely be better off economically by using the four-year conventional rotation (with dry beans), provided growers are willing to ignore the long-term contribution of compost to improve productivity of plant-soil systems,” says the Khakbazan paper on economics.
“Long-term soil quality improvement would have followed on after the 12 years of this study were over in 2011,” adds Larney. “So those conservation plots are likely contributing to higher crop yields out there right now, some five years later.”