Agronomy in a variable farming system

Take home messages

• Farming systems that can rapidly adapt have the greatest ability to manage climatic variation.
• Growers need to match all elements in their system to improve flexibility – equipment, labour, soil type and stubble management.
• Growers must have flexibility in their system and have a number of levers ready to pull when circumstances change – e.g. changing crop type/variety, sowing timing and tactical fertiliser usage to match yield forecasts.
• Perennial pastures and a proportion of trading stock are essential components in managing production variability in a grazing system.

Introduction

Growers have been managing a variable climate since agriculture was first practised in Australia. Their adaptability has allowed agriculture to flourish in an environment very different from their European forebears. A legitimate and challenging question to begin with is, “what is our ‘normal’ climate like”?

Figure 1 highlights the variability in averages over seven-year periods for recorded history in Dubbo. A grower who worked in the 1950-1980 period would have a very different opinion on average rainfall to his/her predecessors, whilst the past 40 years is closer to the long-term average.

Figure 1. Seven-year rolling average rainfall for Dubbo (period from 1894 – 2013).

However, while this highlights changes over longer time frames, it does not indicate variability in a shorter period. It is this shorter-term variability that has a large impact on decision making at the paddock level. For example, will there be sufficient moisture to plant the crop in the desired window, or grow pasture before cold winter temperatures limit growth? Will there be enough rainfall to incorporate applied nitrogen (N) at the desired topdressing stage?

Figure 2 highlights the variability and challenges growers face in Central West NSW when it comes to planting a crop on time. We know that wheat yield declines by 4%-7% for every week a variety is planted outside its window (Matthews et al. 2018), so making the most of limited sowing opportunities is critical. There are a number of areas that farm businesses need to critically analyse to determine if they can minimise yield loss due to climate variability.

Figure 2. Chance of receiving a planting rainfall at Dubbo (Source: CliMate app).

Factors that farm businesses need to analyse to minimise yield loss due to climate variability

Plant, equipment and labour

Given the opportunities to plant based on sufficient soil moisture appear to be decreasing (Figure 2), it is critical a business has sufficient scale in its planting equipment to sow the desired crop area when conditions are suitable. For example, a 10m machine that can operate at 8km/hr, a 16-hour day (after allowing for two hours of maintenance, refilling, etc) could plant 10m x 8,000m/hr ÷10,000m²/ha x 14hrs = 112ha per day. If the cropping program is 2,000ha, this will require 18 days of planting to sow the entire crop. This does not include extra delays due to weather, moving farms, unexpected breakdowns, etc.

The above calculation requires that sufficient labour be available to operate for a 16-hour day. The business may be able to employ extra seasonal labour to operate a longer day but needs to weigh up the costs of potential losses/mistakes if operators are inexperienced. Another alternative is to consider larger equipment, but the extra capital cost of this must be weighed against the decrease in labour demand. Or would the same sized equipment utilising better ground-engaging technology (seed/soil contact, consistent depth, etc) get more crop up on limited moisture?

Any decisions involving plant/equipment and labour must be considered in conjunction with each other. The judicious use of contractors to fill peak demands may be the most efficient and cost-effective means of completing time critical tasks. Contract chemical/fertiliser application is a good example where the opportunity to cover the entire crop area may be limited (too wet, too dry, too hot, too cold, too windy,) and contracting can ensure application occurs in a timely fashion. Timely control of fallow weeds has been shown to significantly increase plant available water at sowing (often 30mm-50mm) and mineralised fallow N (often 30-60kg/ha), usually representing returns on every dollar invested of $3-$8, but sometimes in excess of these figures. In some soils, water use efficiency of moisture stored deep in the profile can be as high as 60kg grain/mm (Cameron and Storrie, 2014). Such returns are more consistent in highly variable environments.

The type of equipment then becomes a serious consideration. For example, disc machines can generally get across the country faster than tines, but often have to wait an extra day or two before they can start planting after rain. Disc machines have limitations when seeking moisture but can operate under heavy stubble loads with precise placement, where more moisture is often conserved, than many tine machines. Investment in effective choppers/spreaders on harvesters can keep the topsoil wetter for longer, but the planter must be able to handle the residue. Thus growers need to consider how soil type, row configuration and stubble management will affect what equipment they will choose to enable them to plant crops as efficiently as possible.

Dry sowing is one means of managing variable sowing rain by having a proportion of crop in the ground prior to rain arriving. All captured rain is then available for germination and none will be lost due to a disc or tine opening the soil. Such a system is dependent on good agronomic practice to have minimal weeds present (particularly annual grasses) and be able to effectively utilise pre-emergent chemistry (most pre-emergents do not perform very well under dry conditions and can cause crop damage when rain is received).

Stubble retention and management

Stubble retention has been one of the cornerstones of zero tillage farming systems, with the key benefit being an increased ability to capture and retain fallow rainfall. Maintaining high levels of ground cover (>65%) and practising zero till has shown to improve fallow efficiency from as low as 10% to as high as 30% (Freebairn 2016).

Retaining heavy stubbles whilst maintaining the flexibility to manage climate variability requires a high degree of management and technology. This may include control traffic and high accuracy guidance for inter-row sowing and/or disc machines or coulters to improve trash handling. Emergence of small seeded crops such as canola may necessitate strategic stubble removal after it has provided its fallow benefits.

Crop and variety choice

Growers can use stored moisture knowledge to select the crop and variety types best suited to a particular field. For example, a field may be switched to chickpeas instead of canola if insufficient moisture is present during the sowing window for canola. Not only does this decision allow for more time to replenish the profile, it utilises a crop that has a lower total water demand.

Within a crop, options are also available to manage variable starting soil moisture. For example, if growing wheat and available moisture is low, a field may be better suited to a low biomass variety than a bulkier one, e.g. Lancer compared with EGA Gregory. The variable nature of autumn breaks (Figure 2) means that growers need to take advantage of sowing opportunities. Research has shown that it is beneficial to plant longer season wheats (e.g. EGA Wedgetail) earlier in order to take advantage of early sowing rains, rather than waiting to plant shorter season varieties (Fettell et al. 2016).

Long season canola is another option available for growers with stock. Planting can occur in the previous spring-summer or early autumn, with grazing able to occur strategically depending on summer/autumn rainfall. The crop is then well established at the time of the traditional canola sowing window. The main challenge to this system in the local area is depletion of the moisture profile that is generally required for spring growth and grain fill. Conversely, if the profile is full at sowing, it gives the opportunity to capture subsequent rainfall and reduce runoff throughout the growing season.

In seasons with delayed breaks, growers could plant short season winter crops such as safflower and linseed. However, these crops have niche markets and variable commodity prices to consider as well.

Central West NSW is challenging for summer cropping due to its limited suitable soil types, unreliable summer rainfall and high evapotranspiration losses. Short season crops such as mungbeans use less water and can be sown to avoid the worst of the hot conditions. The red loam soils of the area have inherently lower water holding capacity, so growers need to carefully evaluate their risk profile when considering such crops. On soils that can hold larger quantities of stored moisture, crops such as cotton and sorghum could be considered.

A lack of understanding how residual chemicals break down is an area for potentially large losses in cropping systems. Many chemicals rely on microbial degradation, which happens most readily under mild, moist conditions. Isolated heavy falls interspersed with hot, dry conditions can easily result in slower breakdown of residues than rainfall totals alone suggest. The summers of 2017/2018 and 2018/2019 are excellent examples of this.

Fertiliser usage

Nutrition is one of the single largest expenses in many dryland crops, so matching requirements to usage is critical. The Central West of NSW is home to a wide variety of soil types, with moisture holding capacities ranging from 50-200mm (sands to heavy vertisols) (Ladson et al. 2004) and soil depth from as little as a few centimetres to tens of metres. An increase in climatic variability means a greater reliance on stored moisture to maximise crop yields. Optimising fertiliser use depends on setting realistic target yields. Assuming a water use efficiency of 20kg/mm moisture, soils holding 200mm could conceivably yield 3t/ha more wheat than a soil that can hold no more than 50mm. Base nutrition would be very different between these two soil types.

The risk of too much N resulting in small grain and ’haying off’ in cereals has long been known. Recent research suggests growers can minimise their N risks in some crops more than others. Application of excess N in canola has consistently shown no negative yield impacts (O’Brien and Street, 2017). Other research has suggested that applying N to wheat any time up until the end of tillering is often equally efficient than earlier applications (Daniel et al. 2017). This allows growers to spread their risk by applying all canola N at (or close to) sowing, whilst being more strategic with their cereals, assisting with both cash flow exposure and logistics.

The ability to apply N in a timely fashion is critical as there may only be one opportunity in front of a rain event. Therefore, the issue of plant and labour affects this decision as well, in other words; the ability to spread urea or spray out liquid fertiliser quickly enough to cover all the required area.

Pastures

For mixed growers, perennial pastures should provide a significant portion of the feed supply system. They are ideally suited to variable climatic conditions for a number of reasons. They do not need to be established every year, therefore respond immediately to available moisture. After prolonged dry spells, species such as lucerne, digit grass and phalaris rapidly produce feed due to their extensive root systems. Annual pastures and fodder crops need to be sown and established before they can provide value to the stock enterprise, therefore are less flexible in the system.

Due to their perennial nature, such pastures only have one establishment cost. This can be significant when averaged over the lifespan of a well-managed pasture. Being neither Mediterranean-style winter dominant rainfall, nor equatorially affected summer rainfall, the Central West does not have a wide range of suitable species of high persistence. Lucerne is by far the most widely adapted but is very much a ’feast or famine’ species. Digit and some other grasses are quite productive if they can be established, but their feed quality is limited. Perennial winter grasses can find it difficult to persist under hot, dry summer conditions. There is room for improvement in our range of perennial species suited to the local area.

(On a side note, there has been some progress in the development of perennial wheat, which would provide many of the advantages of a perennial pasture into a cropping system, but this is some time away from being commercially available.)

Growers need to scrutinise their flock/herd composition in a variable environment. The ability to match feed supply and demand (whilst considering other management issues such as husbandry and markets) greatly influences profitability and reduces exposure to feed shortages. Maintaining a significant proportion of trading stock (whether bred, purchased or both) in the mix allows for strategic reduction in numbers if feed production declines. This not only avoids having to feed all stock, it can delay the start of supplementary feeding for the core stock that remain.

References

Matthews, P., McCaffery, D. & Jenkins, L. (2018). Winter crop variety sowing guide. NSW DPI.

CliMate app

Cameron, J. & Storrie, A. (2014). Summer fallow weed management - manual. GRDC Publishing www.grdc.com.au/GRDC-Manual-SummerFallowWeedManagement

Freebairn, D. (2016). Improving fallow efficiency. GRDC Update (https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2016/02/improving-fallow-efficiency)

Fettell, N., Hunt, J., Flohr B., Haskins, B & Whitworth, R. (2016). Longer season wheat varieties - What are the opportunities? GRDC Updates (https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2016/07/longer-season-wheat-varieties-what-are-the-opportunities)

Ladson, T., Lander, J., Western A. & Grayson, R. (2004). Estimating extractable soil moisture content for Australian soils. Cooperative research centre for catchment hydrology.

O’Brien, B. & Street, M. (2017). High Nitrogen Fertiliser Strategies on Canola. GRDC Updates (https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2017/02/high-nitrogen-fertiliser-strategies-on-canola)

Daniel, R., Kilby, D. & Bailey, L. (2017). Nitrogen Management In Wheat 2016 - Method, Timing And Variety. GRDC Updates (https://grdc.com.au/resources-and-publications/grdc-update-papers/tab-content/grdc-update-papers/2017/03/nitrogen-management-in-wheat-2016)

Contact details

Glenn Shepherd
IMAG Consulting Pty Ltd
glenn@imag.net.au