The many benefits of crop rotation

As part of an article first published in Today’s Farm, John Pettit, B&T Advisor, and Ciaran Collins, Crops Specialist, took a closer look at crop rotation including its ecological, integrated pest management, cost savings and risk management benefits.

As soon as Charles ‘Turnip’ Townshend began practising his four-course rotation of wheat, turnips, barley and clover in England in the 18^th century, yields increased. Today we know why. Crop rotation offers ecological, integrated pest management, cost savings and risk management benefits.

This article evaluates Met Eireann, Central Statistics Office (CSO), industry and Teagasc data to quantify the contribution of rotation to arable farming businesses in south Wexford in recent years.

Weather influence

Success for an arable farmer has always been hugely influenced by the weather. Table 1 (below) shows that recent years have seen shifts in rainfall levels at Teagasc Johnstown Castle. Rainfall in February and March has pushed more spring drilling into April and even May. Crops drilled in late April and May will generally have lower yield potential. Meeting protein specifications for malt barley will be more difficult to achieve. Failing to meet the malt specifications, with a lower yielding crop, is a double hit to the crop’s margin.

Table 1: Johnstown Castle rainfall (mm)

Increased rainfall

The amount of rainfall in September, October and November has also increased significantly. Establishing winter crops is therefore more challenging. Recent years have seen too many poorly established crops due to significant rainfall soon after drilling.

Growing a variety of winter and spring crops increases the opportunities to drill crops in appropriate conditions and within the optimum timeframe. The result is higher crop yield and quality.

Drilling significant areas of individual crops in a short timeframe creates narrower harvesting windows. This inevitably results in crops being cut late, increasing the potential for yield losses and failure to meet market specifications. Table 2 looks at ‘days of rainfall’ at Johnstown Castle over three harvesting periods.

Table 2: Days with no rainfall at Teagasc Johnstown Castle

Between 2022 and 2024 the month of August had on average 12.3 days with no rainfall. This ranged from eight days in 2023 to 19 days in 2022. This highlights the risk associated with harvesting a significant area of one crop. If the same crop was drilled within 10 days, from start to finish, the optimum harvesting period is shortened further, compounding the problem.

Drilling crops like winter wheat expands harvest opportunities. Winter barley, winter oilseed rape and spring beans extend the harvest window into July and September, increasing the days without rainfall from 12.3 to 23.7 days on average between 2022 and 2024. By expanding drilling and harvesting opportunities you also use your labour and machinery much more efficiently realising cost savings.

Herbicide resistance

Another challenge is the increasing difficulty in controlling weeds in winter and spring cereals. Herbicide resistance is increasing. Testing at Teagasc Oak Park has found herbicide resistance to weeds including blackgrass, Italian rye grass, annual meadow grass, wild oats, chickweed, speedwell, corn marigold and poppies.

One of the most significant factors causing resistance is the repeated use of herbicides from the same chemical group. This occurs from the frequent, or continuous, growing of the same cereal crop in the same field year after year. This creates ideal conditions for resistant weed populations to develop. We have seen an increase in herbicide resistance to chickweed and wild oats in recent years, especially in continuous spring barley fields. Resistant wild oats is a growing concern in continuous spring barley.

The 2023 testing of suspected resistant wild oats in Teagasc revealed that 10 out of 14 populations tested were ACCase resistant (Axial, Falcon, Stratos Ultra), while none were ALS (Pacifica Plus) resistant. Chickweed is another problematic weed that has developed resistance, particularly to sulfonylurea herbicides, which are commonly used in spring barley. Samples submitted to Teagasc in 2023 were not controlled by sulfonylurea herbicides (Ally Max, Pacifica Plus and Broadway Star).

A key aspect of crop rotation is the decreased dependence on the same herbicides for weed control. Break crops like oilseed rape and beans offer the chance to control troublesome grass weeds such as bromes, wild oats and annual meadow grass with herbicides from different herbicide groups to those used in cereals. A mix of spring and winter cereals helps to diversify the chemical groups used to control weeds and to slow the development of resistance.

Drilling down into crop rotation data

In Table 3 (below) the spring malt barley data is based on 80% of the grain meeting the malt market specification with the remaining 20% entering the animal feed market. Crops that consistently perform above the mean margin included winter wheat, spring malt barley and winter oats.

Spring malt barley was less profitable than winter wheat in 2020, 2021 and 2022. In 2020 and 2021 this can be attributed to lower premium prices than the 2020 – 2024 average. In 2023 and 2024 spring malt barley was more profitable than winter wheat. In 2023 this can be attributed to a higher premium price than the 2020 – 2024 average while in 2024 it can be attributed to poor winter wheat yields. The financial performance of one crop in comparison to another varies between years. This fluctuation is driven by yield variations due to the influence of weather and prices for grain and straw.

Table 3: Crop margins (€/ha)

Table 4: Price Malt vs Feed (€/tonne)

Risk reduction

By growing a variety of crops you reduce your risk. If one crop performs poorly, another may perform well. This helps to provide a more consistent financial return between years. The average margin of winter oilseed rape at €636 per hectare was the lowest among crops. To achieve an attractive margin for winter oilseed rape in comparison to alternative crops it has to both yield well and have a desirable price per tonne.

Six-year crop rotation

Crop margins should be evaluated over the course of a rotation. The following tables look at three different crop rotation: a winter crop rotation, a continuous malt barley rotation and a combined winter and spring crop rotation. Over the course of a six-year rotation, spring malt barley (SMB) is €60 per hectare more profitable than a winter crop rotation and €37 per hectare more profitable than a combined winter and spring rotation.

When comparing the profitability of rotations, the short and longer term risks and opportunities associated with each, should be considered. Crop rotation with a variety of winter and spring crops can be both practical and economically beneficial by spreading risk, spreading workload, increasing machinery and labour capacity. The experience of tillage farmers in south Wexford shows that when good crop rotation are implemented economic benefits follow.

Table 5: Six-year crop rotation comparisons

Case study: David and Rebecca Kehoe, Ballymurn, Co. Wexford

David Kehoe and his wife Rebecca farm an arable enterprise in Ballymurn, south of Enniscorthy in Co Wexford. Land farmed is generally within a 12km radius of the farmyard. Crops are established with both a plough and non-inversion tine cultivator. Crops on the farm include winter wheat, winter barley, winter rye, winter oats, winter oilseed rape, spring beans, spring malting barley and maize.

“I have adopted a combined spring and winter crop rotation on the farm since 2011,” David said. “The primary reason for adopting this rotation at the time was I had a variety of soil types and not are all were suited to spring barley. Also, winter crops within a rotation offered a more attractive and sustainable margin.”

“Another attraction of growing a mixture of crops is I did not have all my eggs in one basket. It’s a question of spreading risk. In recent years I have expanded the range of crops by adding winter rye and maize.”

Issues with grass weeds

David added: “Many arable growers locally have issues with grassweeds including sterile brome, canary grass and resistant wild oats. Thankfully, I have none of these weed problems, which is a consequence of growing a mixture of crops.

“Since COVID-19 the cost of machinery has risen sharply and good labour is harder to access. Growing a mixture of crops has enabled me to spread my workload and utilise available machinery and labour more efficiently. It is probably fair to say that I am a believer in ‘You reap what you sow’!”

This article was first published in the November/December of Today’s Farm. Access the full publication here.