Diversified crop rotation can replace winter wheat/fallow

On the semi-arid plains, this 6-year crop rotation study found that increasing cropping intensity with spring wheat, pea or lentil could match annualized total grain yields of winter wheat-chemfallow, as long as winter wheat followed a cover crop or fallow.

Winter wheat-fallow rotations are practiced to conserve soil moisture and reduce risk of crop failure due to lack of moisture on the semi-arid plains.  But with adoption of conservation tillage, direct seeding and chemfallow practices, the opportunity exists to expand crop diversity.

A 6-year field study was conducted under dryland conditions from 2008 to 2014 at the Southern Agricultural Research Center, Montana State University, near Huntley, Montana. Huntley is 570 km south of Swift Current, Saskatchewan, where Agriculture and Agri-Food Canada’s Research Centre is located. Annual precipitation at Huntley is around 367 mm from September through August, similar to Swift Current at 350 mm.

Precipitation at Huntley for 2009 – 2011 and 2014 were wetter (411 to 491 mm) than average, and 2012 (199 mm) and 2013 (315 mm) were drier than average.

The objective of this study was to investigate diverse crop rotations to quantify annualized grain yield over time, and evaluate changes in soil quality.

The crop rotations included a 2- or 3-crop rotation of winter wheat, chemfallow, spring wheat, pea, camelina, lentil grain, or lentil as a cover crop. Seven rotations were grown with all crops of each rotation included each year with 4 replications.

Crop rotation treatments and the associated cropping intensity value

aCropping intensity was calculated as number of crops divided by the number of years. The cover crop was terminated at flowering and considered as 0.50 of a full-season crop.

Source: McVay and Khan. 2022

From 2008 to 2011, crops were seeded with a disc drill on 6 inch (15 cm) spacing, and the remaining years with a direct seed air drill on 11 inch (28.5 cm) row spacing. Crop management followed local agronomic practices.

Annualized yield was calculated as the sum of the annual yields of all crops within a rotation divided by the number of crops within that rotation.

When averaged over 6 years, the mean annualized total grain yield of winter wheat–spring wheat–fallow, winter wheat–dry pea–fallow, and winter wheat–spring wheat–lentil cover crop was similar to winter wheat-fallow. The winter wheat–spring wheat–lentil, and winter wheat–spring wheat–camelina had total annualized grain yields slightly but significantly lower than winter wheat-fallow. The pea-winter wheat-fallow rotation had significantly lower annualized grain yield than all other rotations.

Averaged annualized grain yield for each crop within a rotation from 2009 to 2014

Different lowercase letters above each column indicate that the total annualized yield among rotations is significantly different at P < .05. Different uppercase letters within columns indicate that the annualized winter wheat yield among rotations was significantly different at P < .05. W=winter wheat, S=spring wheat, P=pea, L=lentil, Ca=camelina, CC=lentil cover crop, F=fallow.

Source: McVay and Khan. 2022

The greatest contribution to annualized grain yield came from winter wheat when it followed a cover crop or fallow.

Soil water use differed

Soil moisture was measured in 2009, 2010, and 2012 at the beginning and end of June to estimate soil water use by the different crops. Total water use by crop was calculated as the sum of precipitation for the period plus the net change in soil water content to a soil depth of 45 inches (1.15 m).

Spring wheat, winter wheat, and lentil extracted similar amounts of soil water to a depth of 45 inches, although lentil extracted most if its soil moisture from the top 22 inches (0-55 cm).  Spring wheat extracted significantly more soil water in the total soil profile than pea and camelina.

Winter wheat extracted more water from 30 to 37 inches (75 to 95 cm) depth than other crops. Pea, lentil and camelina removed little water below 30 inch depth, and significantly less than winter wheat and spring wheat from the 22 to 30 inch depth (55 to 75 cm). This meant that camelina, lentil and pea extracted soil water from only the top 22 inches during grain fill, highlighting the importance of spring rainfall for these crops.

Soil quality showed few changes

Total carbon, inorganic carbon, and soil organic carbon were similar across crop rotations. Macro-particulate organic matter and total particulate organic matter were significantly higher for cropping intensities of 1.00 compared to a cropping intensity of 0.67. The relatively small changes in soil quality over the study period was likely related to the short duration of the study.

Overall, the stability of winter wheat-fallow systems show the benefits of chemfallow in a semi-arid climate. The results showed that a more intensive crop rotation could provide similar annualized grain yield as winter wheat-fallow, as long as fallow or a cover crop is included in the rotation prior to winter wheat. The researchers felt that the winter wheat-spring wheat-lentil cover crop showed good potential for replacing fallow in the rotation.

The Montana Wheat and Barley Committee providing partial funding for this work.

McVay, K., & Khan, Q. A. (2022). Crop rotation influences yield more than soil quality at a semiarid location. Agronomy Journal, 114, 2280– 2289. https://doi.org/10.1002/agj2.21097

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