Editor's Note: This is part two of this month's look at the spud business. In this installment we build on the composted manure we shared on Monday.

Composted manure can do “wonderful things” for soil health, which, in turn, can boost productivity in agricultural fields, says Utah State University Associate Professor Jennifer Reeve.

“Composted manure improves soil organic matter, water infiltration and retention, nutrient cycling and microbial activity, all of which have direct benefits on crop health,” says Reeve, who focuses her research on sustainable and organic agriculture.

FIELD DAY: Utah State University Associate Professor Jennifer Reeve, here talking with a group of farmers in a Utah onion field, says that composted manure does “wonderful things” for soil, which can boost productivity of a variety of crops.

“Compost can be expensive to apply or sources can be limited, however, so in my research I have focused on figuring out the minimum amounts that can be applied and still have a good effect on soil health,” she says.

For example, in an irrigated corn–squash rotation grown on a silt loam soil, Reeve and colleagues saw no benefits beyond applying 15 tons per acre dry weight with positive effects on crop yield, soil organic matter and available phosphorus four years after application.

“Significant benefits were observed at rates as low as five tons per acre with synergistic effects between low applications of compost and cover crops,” she notes.

In organic dryland wheat, her team has seen residual effects of compost on yield and soil organic matter 20 years after an initial application of 25 tons per acre dry weight.

“We attribute this long-term carryover, in part, to the fact that Western soils are typically low in organic matter with high pH,” she says. “Clearly, compost has positive effects beyond the typical timeframe we might expect.”

Timing is important

When a field is going into potatoes on Flying H Farms in southwest Idaho, the last manure application occurs the fall before planting (this also holds true for other vegetable crops).

Jeff Harper, who owns Flying H with his family, says the fall-before manure application has worked very well for Russet Burbank, Russet Norkotah, Ranger Russet and Teton Russet varieties.

“As soon as we see tubers set—typically 45 days after planting—we’ll do our liquid nitrogen application,” he says.

This system, however, didn’t work well for Bannock Russet, a late-maturing variety, so Harper had to do some experimenting.

“We found that with a fall manure application and an early season liquid nitrogen application, the Bannock would put on vine instead of tubers. To get good tuber set, we found that we had to starve this variety a little in terms of early nitrogen.”

Harper found that the cutoff date for manure applications in fields to be planted in Bannock is June or July the year prior, which is three or four months earlier than the last possible application for the other varieties.

“For some reason, Bannock is a strange critter when it comes to nitrogen.”