What to do with a frosted crop
1. Harvest the grain
Some affected crops will recover after a frost and compensate for lost yield, provided there is sufficient soil moisture and nutrients available. If the damage is minimal and/or occurs outside the critical periods in crop development, the crop may go on to produce a normal crop or experience a slight yield penalty. Estimate the damage and use gross margins to establish the grain yield required to recover harvest costs.
Follow the steps below to estimate the effect of the frost on yield potential:
- Estimate the un-affected yield potential (e.g. 3 t/ha)
- Estimate the proportion of heads not affected (e.g. 7/10 heads will set grain normally)
- Calculate frost affected yield (e.g. 3 t/ha x 0.70 = 2.1 t/ha).
In continuous cropping systems high stubble loads may still be present, despite the reduced grain yield, and need to be managed so that a crop can be grown the following season.
Frost-affected grain is suitable for livestock feed. Research has found that severely frosted cereal grains may have slightly lower energy and digestibility levels than unfrosted crops; however, in all cases, tested levels were within the acceptable range for valuable stockfeeds.
2. Fodder conservation (hay or silage)
Where frost has damaged the head and affected grain filling, cereal crops can be cut for hay. Grain will not form where the head has turned white or brown—although thorough examination of the heads is required for a correct assessment. Consider the demand and opportunity for marketing hay, potential for on-farm storage and use of hay from the frosted crop and the likely costs and returns from haymaking.
Using contractors for cutting, raking, baling and stacking hay can be very expensive. It is important that you have an understanding of the likely market demand before committing to hay making.
A pulse crop with frosted pods early in the season may recover some yield potential through its indeterminate growth allowing flowering and pod set to continue under favourable conditions. If recovery is unlikely, frosted pulse crops can be used for good quality fodder conservation. To estimate the forage yield you can multiply the anticipated grain yield of the crop had it not been frosted by 1.0 to 1.5. If any unfrosted grain is present in the pods, this would boost the forage yield.
There is not the same urgency to cut frosted pulse crops quickly (as it is with cereals), because the feed quality does not decline rapidly after a frost. If there is a lack of soil moisture this may influence the timing of cutting for hay to ensure the crop is cut before leaf drop. By this stage the grain yield is also better known.
A failed cereal crop can be used as standing feed for livestock. Introduce stock to frosted cereal crops after the damage has become visible and potential grain yield versus biomass yield assessed.
Frosted pulses have minimal grain present, so cannot be considered ideal for finishing livestock, even though the forage available is of better quality than pulse stubble residue or a standing frosted cereal crop.
Estimate crop biomass and determine the number of grazing units required. Use gross margins to check if any expense in purchasing livestock would be justified.
In many cases hay freezing the damaged crop before grazing will maximise the fodder quality and rotation benefit. This will maintain feed quality and prevent weed seed set.
4. Green or brown manure
Ploughing in the green crop or spraying out any remaining crop and weeds will return organic matter and nutrients to the soil, manage crop residues and improve soil fertility and structure.
Other factors to consider include planning the crop to be grown on the paddock next year and managing the stubble of the frosted crop, using the opportunity to effectively manage weeds in the frosted paddock, determining if the necessary machinery and contractors are available for conserving fodder and assessing the risk of water or wind erosion on the frosted paddock.
Chapter 5 in ‘Managing Frost Risk’ [http://www.grdc.com.au/Resources/Bookshop/2007/06/Managing-Frost-Risk-a-guide-for-southern-Australian-grains] provides detailed information on the pros and cons of the options above and more.
Plant recovery and compensation in pulses and canola
Time of flowering affects tolerance, and the ability to compensate after the frost has occurred. For example, chickpea often loses early flowers to frost but it can continue flowering as long as water is available, thus compensating for the loss of early flowers.
Canola flowers for a 30–40 day period, so compensatory growth can sometimes occur. A series of consecutive frosts can result in a forced delay of pod set, leading to poor seed fill, especially if a dry finish occurs.
Monitor pod development and seed fill by tagging some reference plants and checking them a few days later for development or senescence (dying).
Plant recovery and compensation in cereals
Sometimes a ‘process of elimination’ is required to decide whether crop damage has occurred. For example, if the anthers are healthy, then check for stem damage. If the stem is severely damaged, then it is unlikely that grain will form properly. If the stem is only lightly or moderately damaged, monitor grain growth and development by tagging some plants and checking them a few days later as experience has shown that grain can form properly if conditions are mild during grain filling.
Testing feed quality of frost-damaged grain
A feed test is necessary to determine the extent of frost damage, particularly any changes to energy or digestibility. Sending a sample of grain to the NSW Department of Primary Industries Feed Quality Service [http://www.dpi.nsw.gov.au/aboutus/services/das/feed-quality-service]. Contact the service before sending samples.