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The planting time and the species in the mix make a difference when it comes to biomass growth.

September 26, 2019

3 Min Read
cereal rye cover crop
BIOMASS THRESHOLD: This cereal rye cover crop is at the threshold (1,000 pounds per acre) biomass level — or about 6 to 8 inches of aboveground growth. Katja Koehler-Cole

By Katja Koehler-Cole

Cover crops have to produce a certain amount of growth, or biomass, in order to effectively reduce erosion and soil nutrient loss, suppress weeds, and supply forage.

Several studies have indicated a threshold or minimum biomass (dry matter) of 1,000 pounds per acre, which is similar to 6 to 8 inches of aboveground growth (see photo above), although more biomass likely will lead to better outcomes.

Cover crops planted after corn harvest have little time to grow. To provide a longer season for cover crops, they can be broadcast interseeded by airplane or high-clearance equipment before corn harvest in late summer. However, their emergence may be low because of the lack of seed-to-soil contact.

University of Nebraska-Lincoln researchers recently assessed whether two types of cover crops, cereal rye (planted at 60 pounds per acre) and a mix (30 pounds per acre of rye, 20 pounds per acre of winter pea, 8 pounds per acre of hairy vetch, 4 pounds per acre of brassicas), planted either before corn harvest or after corn harvest, would achieve the biomass threshold of 1,000 pounds per acre.

The preharvest planting was carried out by spreading seed by hand into corn stands in September to simulate broadcasting either by high-clearance equipment or aerial seeding. The postharvest planting was carried out with a no-till drill between mid-October and late November. Researchers conducted trials at three research stations in south-central, eastern and northeast Nebraska over four years (2015-18).

Rye cover crop spring biomass production in pounds per acre chart

FIGURE 1: Rye cover crop spring biomass production in pounds per acre (average of four years) at the eastern, northeast and south-central sites.

In eastern and northeast Nebraska, the preharvest planting achieved the biomass threshold (Figure 1), producing on average 1,900 to 2,500 pounds per acre of biomass by late April to early May, while the rye planted postharvest produced about half of that amount. Cover crops planted preharvest had lower emergence than cover crops planted postharvest, but had more time to grow and tiller, compensating for low populations.

In south-central Nebraska, both planting times reached the threshold, but the postharvest planting produced more biomass. This site receives less rainfall in the fall, restricting the emergence of preharvest cover crops.

Mix and rye cover crop spring biomass production in pounds per acre averaged across eastern, northeast and south-central sites  chart

FIGURE 2: Mix and rye cover crop spring biomass production in pounds per acre averaged across eastern, northeast and south-central sites and both planting methods for all four years.

Overall, the mix biomass was lower than the rye biomass (Figure 2). The brassicas in the mix winter-killed, and hairy vetch and winter pea produced very little growth. So, the mix can be thought of as rye planted at 30 pounds per acre. Despite this low seeding rate, the mix produced more than the threshold biomass at the south-central sites in both planting times, and at the northeast site in the preharvest planting (Figure 3).

Mix cover crop spring biomass production in pounds per acre (average of four years) at the eastern, northeast and south-central sites chart

FIGURE 3. Mix cover crop spring biomass production in pounds per acre (average of four years) at the eastern, northeast and south-central sites.

Cover crops will only achieve their purpose and be successful if they produce sufficient biomass. Best management practices for cover crops in northeast and eastern Nebraska should focus on planting preharvest and planting rye. In south-central Nebraska, postharvest planting is more productive, and mixes may be as productive as rye.

The Nebraska Corn Board and Nebraska Soybean Board provided funding for this project.

Koehler-Cole is a research assistant professor in the Department of Agronomy and Horticulture at the University of Nebraska-Lincoln.

Source: UNL CropWatch, which is solely responsible for the information provided and is wholly owned by the source. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.

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