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Organic Transition Approaches for the Northern Great Plains
J.G. Franco, D.W. Archer, J.J. Halvorson, J.R. Hendrickson, S.L. Kronberg, M.A. Liebig, M.A. Sanderson
USDA-ARS Northern Great Plains Research Laboratory, Mandan, ND
Introduction
North Dakota ranks in the top 5 nationally in organic acreage (ERS 2016) and more research is needed to help inform this rapidly growing sector. For organic producers, cover crops are an essential tool to maintain soil health, provide pollinator services, control weeds, and potentially facilitate a transition to reduced tillage. The limited weed control options available to organic producers are further limited under conservation tillage. This study was designed to evaluate six transition approaches under conservation tillage including four annual cover crop mixtures, a perennial forage, and an annual crop rotation system. To further evaluate weed control benefits, a grazing component was added to compare grazing effect on plant community dynamics.
Materials and Methods
Study SiteA 3-yr study was initiated in 2016 at the Northern Great Plains Research Laboratory in Mandan, ND (lat. 46°46’35”, long. 100°54’20”). The climate in central ND is considered semi-arid with mean annual precipitation of 456 mm and a mean annual temperature of 4°C. Study site soil is classified primarily as a Tally fine sandy loam with gravelly substratum (coarse-loamy, mixed, superactive, frigid Typic Haplustolls). The site had previously been used for no-till hay production but was chemical fallowed in 2015. The site was lightly disced and sprayed with glyphosate in spring 2016 to reduce the weed seed bank prior to planting and prior to beginning the organic certification process.
Treatments and ManagementA 6 x 2 factorial design was used with cropping treatment as the main plot factor and grazing level (grazed vs. ungrazed) as the split plot factor (n = 4; Fig. 1). The six cropping treatments with crops for 2016 and 2017 are listed in Table 1. All treatments were planted in mid-June both years. A fall-seeded rye/red clover mixture was planted in all treatments in October 2016. In the annual crop rotation, a weed suppression cover crop mixture was planted in 2016 then converted to an annual crop rotation beginning 2017 by harvesting rye grain which was seeded fall 2016. A buckwheat cover crop was planted following rye harvest when adequate moisture was available (mid-August). Grazing with similar animal units across all four replicates occurred in mid-August in 2016 and in mid-October in 2017.
SamplingThree 0.33 m2 biomass harvests per split plot were conducted just prior to cattle grazing and separated by cover crop species and weed biomass. Results are presented on a dry matter basis.
Discussion•Lack of timely precipitation in 2017 (Fig. 4) reduced weed biomass (Fig. 3b), but also reduced annual cover crop productivity (Fig. 3a) as compared to the perennial treatment or treatments with high cc “volunteer” biomass (Fig. 5).
•Results also show that cover crop “volunteers” may be managed with grazing.
•Variable and unreliable precipitation (Fig. 4) may support the use of perennial forages during the 3-yr transition period.
•Matching timing of grazing to meet feed requirements (fall) with grazing to reduce the weed seed bank is a critical challenge.
•Analysis of soil and pollinator resource benefits, as well as the impact of these different approaches on certified organic cash crop yield and quality will be conducted.
•Economic analysis will further help producers weigh the costs and benefits to each organic transition approach.
Preliminary Results
First author contact: [email protected]
Fig. 3. Total biomass production for (a) all cover crops (summed for all crops) and (b) all weeds (summed for all weed types) in 2016 and 2017 by grazing and cover cropping treatment. There was a significant effect of treatment nested within grazing treatment (P ≤ 0.05) in 2017.
Fig. 4. Growing season precipitation (mm) near the study site in Mandan, ND in 2016 and 2017.
Fig. 5. Total biomass production with proportional contribution of volunteer cover crops in 2017.
Table 1. Organic transition treatments with crops planted in 2016 and 2017.
Fig. 1. Organic transition study treatment design showing replicate 1 of 4.
Per
enn
ial
Soil
Bu
ildin
g
Wee
d S
up
pre
ssio
n
Mu
ltip
urp
ose
An
nu
al C
rop
Po
llin
ato
r
Per
enn
ial
Soil
Bu
ildin
g
Wee
d S
up
pre
ssio
n
Mu
ltip
urp
ose
An
nu
al C
rop
Po
llin
ato
r
buffer
Ungrazed
Grazed
(a) (b)
5363
123
239
5344
336
6
41
59
106 112
42
260
0
50
100
150
200
250
300
350
400
May June July May-July Total August September GrowingSeason Total
Pre
cip
itat
ion
(m
m)
2016 2017
Fig. 3. Images showing examples of biomass production and cattle grazing in (a) 2016 and (b) 2017 in Mandan, ND.
(a) (b)
Year Annual Rotation Perennial Soil Building Weed Suppression Pollinator Multipurpose
2016 winter rye alfalfa sorghum-sudan winter rye phacelia winter wheatforage oat interm. wheatgrass winter wheat buckwheat sunflower German milletGerman millet winter triticale sweet clover rapeseed
red clover mustard buckwheatcowpea field pea
soybeanFall-seeded rye/med red clover rye/med red clover rye/med red clover rye/med red clover rye/med red clover rye/med red clover
Year Annual Rotation Perennial Soil Building Weed Suppression Pollinator Multipurpose
2017 late-seeded buckwheat Siberian millet buckwheat borage winter ryeannual ryegrass mustard wild sunflower sorghum-sudansoybean carinata kalefield pea black medic sunflower
faba bean sweet cloversunnhemp
Acknowledgements: The authors would like to thank Holly Johnson, Andrew Carrlson, Clay Erickson, Justin Feld, Robert Kolberg, Delmer Schlenker, Stephanie Schmidt, Dawn Wetch and all
who have helped with field work and management. USDA is an equal opportunity provider and employer.
