*For the purpose of this article, when referring to a summer crop the article is referring to millet or sorghum
Tom Farran, DEPI Tatura
It is approaching that time of year when many farmers are weighing up their summer feed options. Over the last couple of years many farmers in northern Victoria have been growing a summer crop to fill the common feed gap experienced on many farms at that time of year. This article is going to explore some of the key learning's and mistakes local farmers have made over recent years and what tips and advice they collectively have that can help get the best out of a summer crop.
While summer crops may be green and look impressive on a scorching hot summer's day, the reality is they can only be described as moderate quality feed for dairy cows. Generally the taller they get the poorer the quality will be. Another factor that can often be overlooked is summer crops can have quite low amounts of some minerals.
Due to the lower quality and higher fibre content of summer crops, you will need to restrict the total amount in the cow's diet if you want to maintain a relatively good milk production level over summer.
The grazing management of a summer crop has a significant influence over the quality of the feed the cows ingest. Making sure the crop is always grazed as soon as it is ready helps to achieve a high quality crop. It is important that minimum plant height guidelines are adhered to for sorghum prior to grazing to avoid animal health issues.
Farmers who have been grazing millet every time it reaches about gumboot height have found the cows have been milking much better off it compared to when they used to graze it at about knee height.
The taller a summer crop gets the more mature it is. The quality drops off very quickly as the crop matures. Summer crops are very unforgiving in this regard.
To maintain good production it will be necessary to make sure some higher quality forms of feed are also going into the diet. This may be good quality pasture and high quality home-grown conserved fodder. For other farms this may mean purchasing in high quality supplements and fodder. Developing a plan including a feed budget is time very well spent. This plan will most likely need adjusting as the season progresses, but at least it is a starting point and is a way of making sure you have thought about it and sought advice if needed.
Amount of area to grow
A big mistake often made when growing summer crops is to sow too large an area. The issues with this are:
- it is harder to maintain grazing pressure which results in poorer quality feed;
- cows can not physically keep up with the growth; and
- the crop uses up too much water.
Summer crops are sporadic in the way they grow, sorghum more so than millet. They respond very quickly to the weather. During hot weather, particularly if it is humid, they will grow very rapidly. However, if they experience some cool days their growth slows dramatically. The issue farmers often have is if they have a large area of summer crop and the growth rapidly accelerates, they can not simply speed up the rotation because the cows are already eating as much as they can. The catch is if they can not speed up the rotation then the quality of the crop rapidly declines. If paddocks then get skipped over instead of being grazed and are made into silage, the costs involved (planting, growing, watering and conserving) are normally much higher than a substitute feed of similar quality could have been purchased for.
To maintain a good milk production level there is a limit to the amount of average - poor quality feed a cow can eat. This factor is a good determinant of how much summer crop to grow on your farm. A very rough rule of thumb to use is the total amount of summer crop being eaten should not exceed seven to ten kilograms of dry matter per cow per day depending on the size of the cow and your production targets. For example, if a summer crop is expected to grow at one hundred kilograms of dry matter per day during its peak on one hectare of land, then the maximum amount of summer crop that should be grown is one hectare for every ten cows (100kg/DM/ha of expected production÷ 10kg/DM/cow dietary limit).
Irrigation water is another consideration. For many farms the sums may add up at the current price to purchase temporary water to grow a summer crop. However, consideration still needs to be given to the total amount of water needed for the farm this irrigation season. You need to make sure you will stay inside your annual water use limit. A water budget is vital to make sure this is going to be achieved. The best use of water in this region has been proven to be during spring and autumn and on good quality perennial pastures over summer. So it is very important to make sure there is enough room left inside your annual use limit to irrigate these crops and pastures first before irrigating a summer crop.
In ideal conditions millet will be ready to be grazed for the first time after approximately five to six weeks when the plants are well anchored in the soil. It can then be grazed every ten to twenty days until March. Begin grazing millet at a height of 25-30 centimetres in order to achieve maximum quality. Previously the common recommendation was to wait until the plant reached 60 centimetres (knee height). However the farmers who have been grazing it at 25-30 centimetres have found a far better milk response and also a much greater ability to stay in control. It is likely that by grazing at 25-30 centimetres the total yield will be lower, but the trade off for better quality feed offsets this.
Only graze the millet down to a height of ten to fifteen centimetres (ankle height). Grazing below this height will 'eat' into the plant reserves and as a result regrowth will be compromised. It is important not to wait too long before re-grazing as the quality declines sharply as the plant matures and future regrowth is poor if plants are allowed to go rank.
Most sorghums can not be grazed until they reach a certain height due to the risk of prussic acid poisoning. This height varies for different varieties and this information should be made available to you when purchasing the seed.
The taller the sorghum gets the poorer the quality will be, so for most sorghums it is best to graze them as soon as it is safe to do so and graze them down to around fifteen centimetres in height. To avoid the risk of prussic acid poisoning, do not graze sorghum until it has reached a height greater than the recommended height for the variety (usually 60 centimetres but varies with different varieties). Do not graze the sorghum when it is drought stressed, water logged or stressed for any other reason. It is normally fairly obvious to determine if sorghum is stressed as its colour turns purple/blue. Never put hungry stock onto sorghum and if possible offer them hay or a runoff paddock when grazing it for the first grazing. Sulphur stock blocks may help reduce some animal health risks of sorghum, but should not be relied on.
Preparation and fertiliser
Careful planning, preparation and timing are critical to growing a good profitable summer crop. Making sure soil bed preparation and sowing methods are appropriate, providing adequate fertiliser, managing irrigation well and making sure all operations happen on time are all critical ingredients to growing a good crop.
Timing is critical with summer crops. Everything happens quickly and being a couple of days late with something often spells disaster.
Summer crops are high yielding crops. This means they require high amounts of nutrients to achieve this. If you attempt to skimp on fertiliser you will get lower yields. Also beware, skimping on fertiliser will have an impact on the next crop or pasture grown as the summer crop will have mined nutrients from the soil, particularly nitrogen and phosphorus.
For summer crops to be a profitable crop, the two key ingredients needed to achieve this are good yields and good quality. Trying to save money on establishment costs (fertiliser and soil preparation for example), will often dramatically reduce the yield. Without good yields all the costs involved in growing the crop can not get diluted. If the crop is not managed well and the quality declines then this will always be an expensive feed on a dairy farm as there is very limited room in a cow's diet for poor quality feed.
Top lessons learned
- Do your sums to determine if a summer crop would provide the most cost effective form of feed.
- Summer crops are no silver bullet in terms of quality.
- Limit the area of summer crop gown in order to:
- Stay in control;
- Minimise milk production losses;
- Avoid having to conserve.
- Do a feed and water budget to determine:
- Whether a summer crop is needed, or will you already have enough feed;
- If it would provide the right quality of feed you need;
- How much area to sow;
- If you have enough water to spare inside your annual water use limit.
- Graze summer crops frequently to maximise quality:
- Millet grazed at 25-30 centimetres in height;
- Sorghum at the minimum height that is safe.
- If the summer crop starts to get out of control – take decisive action immediately.
- Do proper preparation and do not take short cuts. Make sure you apply adequate fertiliser or you will be disappointed with the end result.