The development of short season corn varieties that are suitable for corn grain production in Manitoba and favorable corn grain prices have been driving an increase in corn acres and expanding the growing area for corn in Manitoba. Major breeding efforts are underway to develop short season corn that is better adapted to prairie growing conditions. Agronomic best management practices and recommendations that are specific to crop rotations, soil types, and the environmental conditions of Manitoba are needed to enhance the success of current and new corn growers. Important agronomic issues to address in Manitoba in the short term include: crop rotation, residue management, phosphorus fertilization, corn row spacing, and improvements to the corn heat unit systems.

This research project has engaged and establish a network of scientist at the University of Manitoba to work on corn agronomy issues. In a short period of time, we have learned much about how to adapt and optimize corn agronomy for Manitoba growing conditions. We have also identified some research questions that warrant further study, such as the evaluation of corn heat units in Manitoba. Several graduate students were involved with this research project. The training they receive in corn agronomy has already begun to make an important contribution to the corn industry as they graduate and have begun their careers in Manitoba.

Major Findings by Project Objective:

Objective 1: Identify the best crops to grow prior to corn in a rotation

Dr. Yvonne Lawley and Dr. Navneet Brar (PDF), University of Manitoba

• Growing crops that host mycorrhizae (soybean, corn, wheat) the year before to corn promoted early colonization of corn roots by mycorrhiza and increased early corn growth.
• Growing crops that were non-hosts for mycorrizae (canola) the year before corn decreased early season corn biomass and P uptake. Mycorrhizal colonization of corn roots was delayed early in the season but caught up around the silking stage.
• Preceding crops did not affect the grain yield of following corn crop. However, corn following canola had a 1-3 day delay in silking compared to other preceding crops. This delayed corn grain dry down following canola compared to wheat. Thus having the potential to increase grain drying costs.

Objective 2:  Crop rotation and P fertilization

Dr. Don Flaten and Magda Rogalsky (MSc student), University of Manitoba

• Starter fertilizer benefits are greatest when corn is planted after canola;
• Starter fertilizer placed in close proximity to the seed at planting in our northern corn production system allowed the corn plants to have excellent access to P.
• Corn growers can use starter fertilizer to realize the benefits of accelerated maturity, increased grain yields and reduced grain moisture at harvest, resulting in increased net returns;
• Accelerated maturity and lower grain moisture allow farmers to harvest short-season hybrids 3 to 7 days earlier, further reducing their risk against fall frost damage and potentially poor harvesting conditions;
• Alternatively, accelerated maturity and lower grain moisture enables corn growers to grow longer-season, higher-yielding corn hybrids at the same level of risk as shorter season hybrids grown without starter fertilizer;
• Side-banded P at planting is agronomically superior to precision fall deep-banding for corn, keeping in mind that our fall deep-band placement was deeper compared to most common fall applications in MB;

Objective 3:  Economic Analysis of optimal crop rotations involving corn

Dr. Derek Brewin, Hazel Sakulanda (MSc Student), and Liting Yi (MSc Student)

Using Manitoba Agricultural Services Corporation (MASC) data from 2008 to 2012, Anastasia Kubinec calculated the average impact on yields of crops grown in various rotations in 2014. She estimated the impact of the crop choice in the previous year on various crop yields, relative to the 2008-2012 average for that seeded crop.  For example, winter wheat planted into the stubble of a previous winter wheat crop yielded 78% of the average winter wheat yield. A 22% drop from average yields. Winter wheat planted into canola stubble yielded 104% of the average yield.  Continuously cropping of the same species has a significant negative impact on yield for all of the crops listed.

As part of her thesis for a Masters in Agribusiness, Hazel Sakulanda began with Manitoba Agriculture cost of production budgets from 2016 and set out to explore the implications of these yield connections through as many as five years of different crops grown in rotation.  She used five year average prices from MASC.  Sakulanda focused on the five largest crops grown in rotation in Southern Manitoba.  Using five year average prices and yields and 2016.  With out adjusting for rotational considerations and average yields are used, corn comes out as the best return per acre.  However, if that single simple budget was used every year to choose the best returns corn might be planted on corn.  That choice would have a negative impact on yield of 13% as estimated by Kubinec (corn grown on corn stubble gets 87% of the average yield).

Taking the yield impacts of into effect, Sakulanda considered over 3,800 combinations of five, four, and three year rotations.  The top five are shown in Table 1 along with some other rotations to give you the relative changes rotations can make. No three year rotations were in the top five although canola, soybeans and corn had the 9^th highest average return. All of the top ten rotations contained corn and soybeans.  Four of the top ten had wheat and two of the top five included canola.

Table 1. Rank of Average Net Returns for Various Rotation Options.

(Source: Sakulanda, Manitoba Agriculture, and MASC).

The economic impact of continuous cropping is clear.  Continuous corn crops average $57 per acre less than soybeans and corn grown in rotation. Continuous canola earns $64 per acre less than canola and wheat grown in rotation and continuous wheat earns $79 less.  Soybeans’ impact on other crops is also clear. Even though it is the third most profitable crop in average budgets, its positive impact on other crops makes it a very profitable choice within rotations. Soybeans were part of all of the top ten rotations.

Objective 4: Identify optimum corn residue management strategies. 

Dr. Yvonne Lawley and Patrick Walther (MSc student)

The impact of different tillage equipment to manage corn residue was evaluated based on soil temperature, soil moisture, and the response of a soybean test crop. Field trials were conducted over a three year period (2014-2016). The experiments were set up as on-farm trials in four locations in Manitoba on sandy soils. The trials were randomized and replicated in farmer’s fields. Four tillage practices were compared: 1) conventional double disc; 2) vertical till high disturbance; 3) vertical till low disturbance; 4) strip till

Surface residue cover varied significantly among corn residue management treatments, ranging from 29 to 65%. Around the time of planting, daily surface soil temperature at 5cm varied among treatments only during the peak and low temperature points of the day. Overall, all tillage treatments grouped together in contrast with the undisturbed soil treatment between strip till rows (Appendix 1). Soil temperature trends were not always consistent between siteyears. Planting and rolling operations for soybean had an influence on maximum and minimal soil temperature patterns. During soybean emergence, soil temperature at planting depth (5cm) showed no differences among treatments in total accumulated as well as daily accumulated soil temperature above 10°C at any siteyear. In this study only two out of four siteyears had higher moisture contents over a longer period of time in the un-tilled part of strip till. At planting, all treatments at all sites had the minimal volumetric soil moisture threshold of 0.096 m³ m^-3 required for soybean emergence. Despite differences in absolute soil temperature and moisture between residue management treatments, no significant differences in soybean emergence and final plant stand were observed in three out of four site years. At harvest, soybean grain yield was not statistically different among the corn residue management treatments (p=0.6267, CV 6.7%)..

Economic analysis showed time and cost savings for strip till. For the analysis, costs due to management practices such as seeding rate and crop protection were kept the same among treatments. Revenue calculated from soybean yields were also the same due to a lack of statistical differences between treatments in the experiments. Thus, differences in economic return are therefore driven by the cost of the tillage systems compared. Total costs for corn residue management treatments were: double disc (32.25 $/ac, including 2 passes), vertical till high disturbance (31.7 $/ac, including 2 passes), vertical till low disturbance (29.72 $/ac, including 2 passes) and strip till (19.31 $/ac, only one pass required). Using the average farm size for Manitoba of 1134 ac, strip till could save the farmer $11,805 compared to vertical till and $14,674 compared to double disc per year. Furthermore, strip till as a one pass system practiced across an average farm of 1134 acres, showed time savings of 1.1 to 3.7 days compared to vertical till and double disc, respectively.

This research project has provided information that was not previously available to help corn growers in Manitoba evaluate residue management practices in side by side replicated field scale experiments. The results of this study indicate that farmers have many tools that will allow them to manage corn residue and grow a successful crop after corn in Manitoba. Both vertical tillage and strip tillage show promise as alternatives to managing corn residue with a double disc in Manitoba. However, when interpreting the findings of this study it is important to note that all the siteyears were conducted on sandy soils. Further research on heavy clay soils is still needed. 

Objective 5: Evaluate fertilization strategies for alternative tillage systems for corn production

Dr. Don Flaten and Magda Rogalsky (MSc student), University of Manitoba

• Fall strip tillage systems for corn production can provide the soil conservation benefits of reduced tillage compared to conventional tillage, without any yield loss or other agronomic penalty.
• Starter fertilizer placed in close proximity to the seed at planting in our northern corn production system allowed the corn plants to have excellent access to P.
• Starter fertilizer enables corn growers to realize the benefits of accelerated maturity, increased grain yields and reduced grain moisture at harvest, resulting in increased net returns;
• Accelerated maturity and lower grain moisture allow farmers to harvest short-season hybrids 3 to 7 days earlier, further reducing their risk against fall frost damage and potentially poor harvesting conditions;
• Alternatively, accelerated maturity and lower grain moisture enables corn growers to grow longer-season, higher-yielding corn hybrids at the same level of risk as shorter season hybrids grown without starter fertilizer;
• Side-banded P at planting is agronomically superior to precision fall deep-banding for corn, keeping in mind that our fall deep-band placement was deeper compared to most common fall applications in MB;

Objective 6: Evaluation of corn heat unit system for Manitoba

Dr. Paul Bullock, Justice Zhanda (MSc student), Dr. Lana Reid

The rate of corn development was evaluated in 2015 and 2016 at 6 sites in Manitoba and 2 sites in Alberta spanning a cross-section of climatic and soil conditions in Western Canada.  At each site, the phenological development of the exact same hybrids was tracked using onsite cameras which captured several photographs each day to accurately determine the dates on which each different hybrid reached specific stages of development.  Portable weather stations tracked hourly changes in weather conditions at each location throughout the growing season and provided air temperature data for calculating heat unit accumulation at each site.

There was a strong correlation between relative maturity (RM) rating (used by seed companies to development heat unit ratings) and corn heat unit (CHU) accumulation calculated from daily temperature. This is especially the case for hybrids with 72-76-day RM rating and 2200-2500 CHU, which are normally considered the most suitable hybrids for the Prairies.

There was an insufficient number of sites and years to uncover significant differences in accumulation of days or heat units to any stage of corn development, despite the fact the corn hybrids in the study had CHU ratings ranging from 2200 to 2700.  All of the corn hybrids accumulated more CHU to reach physiological maturity (PM) than suggested by their CHU ratings.  Across all site-years, average accumulated CHU to PM ranged from 78 to 538 CHU above the hybrid rating (Table 1).  This is a significant issue that will potentially limit grain corn expansion into non-traditional production areas because of the risk involved in its production and the lack of a reliable indicator to assess the risk.

The coefficient of variation (CV) for all indices was highest at the VE and V2 stage but declined to 10.5% or less at PM. Although the differences in CV among thermal units were not significant, the data indicated that the General Thermal Index (GTI) may be a better index than CHU and the other indices because its CV was under 5% at PM for all corn hybrids in the study.  This means that the GTI index appears to accumulate consistently across a wide variation of soil and climatic conditions and should be further assessed because it has potential to be a superior alternative to CHU and other indices.  Greater consistency in heat unit accumulation ratings would improve the information provided to producers for selecting appropriate grain corn hybrids for their specific locations on the Canadian Prairies.  It should be noted that if further study reveals the GTI thermal index is superior to CHU, additional research on climate risk will be required to determine the long-term probabilities for GTI accumulation by region on the Canadian Prairies. Currently this assessment exists for only CHU and standard growing degree days (GDD) but not for other thermal indices, including GTI, tested in this study.

More frequent cold night temperature exposure resulted in reduced total CHU accumulation from planting to PM for one of the hybrids but had inconsistent effects on CHU accumulation for the other hybrids. GTI accumulation from planting to PM was relatively unaffected by cold night temperatures.

Table 1. Grain corn hybrid CHU rating and accumulated CHU to PM for 5 corn hybrids.