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1. Project Name: Spring grain performance following various cover crop mixes in southcentral

Montana

2. Investigators:

a. Kent A McVay, Cropping Systems Specialist

b. Qasim A Khan, Research Associate

early in the previous century prior to the availability and use of modern fertilizers. There is less

information on the impact and needed composition of mixed species cover crops to perform the

functions of improved plant diversity, reduce C-N ratios of residue returned, improved water

infiltration, amelioration of soil compaction, and addition of organic nitrogen to the soil system.

The use of mixed cover crops has mostly occurred in regions of ample or at least greater

precipitation than what is received in the semiarid region of the northern Great Plains. This

study was initiated to provide a location where mixed cover crops are included in a spring grain

cropping system to allow changes to soil quality to approach an equilibrium in order to quantify

their impact on crop production and soil quality.

before quantifiable changes in soil quality can be documented. The impact of four different

plant species, or ‘functional groups’ will be compared.

5. Methods: Mixed species cover crops and a chemical fallow were established using a randomized

complete block with 4 replications in early May of 2015 and 2016 in field J at the Southern

Agricultural Research Center. Each group was composed of at least one warm and one cool

evaluate the impact of cover crops on nitrogen response of the spring grain. Nitrogen rates were

based on yield goals using MSU recommendations. Rates are 0, 0.5, 1.0 and 1.5 times the MSU

recommendation for spring grain reduced by soil nitrate content in a 4 foot profile measured

prior to planting. Targeted plant populations (Table 2) were adjusted by species within a group

(for example in the legume group the target population for each species was reduced by a factor

of 4 since there were 4 species in that group), and when mixed across groups, by a factor of the

numbers of groups within a mix (either by 3 for mixtures minus one group; or by 4 for the ‘All

and made level using a garden hoe. A ring was placed on the soil surface where fine sand was

added and then leveled to provide a good contact for infiltration. Rates were measured at -15

each tension. Saturated conductivity was calculated from these tension measurements using

Wooding’s equation.

6. Results: The year was a wetter than normal year (Table 1) with over 15 inches of precipitation

received between March 1 and August 31 where the historical average is 9.3 inches. It was also

in time for uptake by the wheat crop.

Cover crops yielded well for the most part in the west block averaging over 2200 lbs of dry

matter (DM)/acre (Table 4). The exception was the brassica treatment which only yielded 777

lbs DM/acre. This trend was similar to 2017 where the brassica treatment only yielded 315 lbs/a

while the rest of the treatments yielded biomass from 1833 to 3572 lbs/a. Looking only at the

factor may be needed to better even out biomass contribution by cover crop species. The

competitive ability of each functional group or species should be considered in order to attain a

Soil properties were determined at the end of the growing season following cover crops in the

west bench. Total soil water was measured gravimetrically and summed for the profile (Table 5).

The main difference was expected where fallow retained more water (11.4 in) stored in the

profile than where cover crops were produced. On average nearly 4 inches more water had

been stored in the profile under fallow management as compared to cover crop treatments. The

exceptions are the brassica mix treatment which had a total of 8.5 inches stored and the All

statistical differences between treatments was found. In fact the fallow treatment had the

greatest numerical measure of aggregate stability which was unexpected, but falls in line with

our initial suggestion that in order for significant changes in soil properties to occur several

cycles of cover crops will needed.

To assess the long-term impact of cropping systems on total biomass returned over time,

estimates of straw yield from the small grain phase were added into the cumulative biomass

estimates by cover crop treatments (Table 8). It was apparent that legumes provided lower

Table 1. 2018 weather summary for Southern Agricultural Research Center, Huntley MT

Table 2. Target plant populations for each species in cover crop study, Huntley MT 2018

Table 3. Performance of spring wheat following various cover crop and nitrogen fertilizer treatments,

Table 5. Total soil water (in) by depth increment following various cover crops measured in fall after

Table 7. Stability of 2-4 mm aggregates following various crop crops measured in fall 2018, Huntley MT.

Chart 1. Dry matter accumulation by functional group within a cover crop mixture, Huntley MT 2018.