DROUGHT IN MAIZE SILAGE
Harvesting, Storing and Feeding Drought Affected Maize for Silage
By Barry McCarter, Maize Product Manager and
Dr Jakob Kleinmans, Forage Products Manager
High temperatures combined with a lack of rainfall can cause drought stress in maize crops. Although nothing can be done to influence the weather, there may be some available management decisions that could minimise the impact of the drought on the utilisation of the crop. Droughts in New Zealand are usually short term in nature and the main effects are moderately reduced yields. However, in more extreme seasons yields and crop quality may be more compromised.
This paper seeks to provide information to assist growers in the following general areas:
TIMING AND EFFECTS OF DROUGHT ON MAIZE
Most maize paddocks are likely to experience some limitation to available soil moisture at some point during most growing seasons. Some reductions in yield may have occurred even in seasons when maize yields approach 12 tonnes of grain or 20 tonnes of silage drymatter per hectare. The onset of drought conditions is primarily caused by inadequate soil available water which is a function of rainfall and soil water holding capacity. In principle, maize crops on sandy soils will encounter drought stress sooner than crops grown on sandy loams or peat soils.
In some regions available soil moisture is progressively being depleted from the root zone due to high summer temperatures, wind and insufficient rainfall. As a result, some growers have expressed concern about the future yield potential of these crops. Late planted crops may encounter stress relatively earlier in their growth cycle, likely before or at pollination.
Drought stress at pollination
The period two weeks before silking through to two weeks after pollination is the most critical in terms of the impact of drought on yield. During this period the total number of kernels per cob is being determined.
Water demands by the plant are high during pollination, especially for silk elongation, pollen germination, and pollen tube growth. Under drought conditions, silk emergence may be delayed compared to pollen shed. If this delay is more than several days, there may be a limited amount of pollen when silks emerge. This can result in incomplete pollination and a reduction in the number of kernels. As the last silks to appear come from the tip of the ear, barren or poorly filled cob tips can result. Drought and high temperatures can also lead to desiccation (drying) of silks, causing poor pollen germination and pollen tube growth. This may also result in a reduced number of kernels.
In addition to disrupting pollination, drought during the early grain fill period can result in kernel abortion. This means that the kernels pollinate but fail to develop. The kernels at the tip of the cob are the most susceptible to abortion particularly during the first two weeks following pollination. As a result of the critical relationship between available moisture, successful pollination and early kernel development, yield losses may be as high as 5 percent per day when severe drought occurs during this period.
Drought stress during grain fill
During the grain fill period, kernel size is being determined.
Drought stress during the dough and dent stages of grain fill decreases yield primarily due to decreased kernel size, rather than decreased kernel number. Drought reduces the rate of photosynthesis in the plant, resulting in less carbohydrate production and less nutrients for production. Drought may also cause premature maturity or black layer formation in the kernels which terminates starch accumulation. If drought is so severe that leaf or plant death results, yield will be significantly reduced. Finally, drought often results in stalk rot development, which can reduce harvestable yield. Researchers estimate that drought stress during the fill stages of development can cause yield losses of up to 3 percent per day.
Figure 1: Stress during grain fill can result in tip die-back or kernel abortion.
WHEN SHOULD DROUGHT STRESSED MAIZE SILAGE BE HARVESTED?
Maize has a remarkable ability to recover from drought stress when normal levels of moisture return, so silage harvest should be delayed as long as possible.
Maize silage with little grain development should be harvested when no further quality and yield development can be expected. Crops with some grain development and the presence of green leaves above the cob can still increase in yield and quality, because they can continue to deliver nutrients to the cob.
Once the upper leaves do not recover overnight and start to dry, the maize should be harvested. As the grain is poorly developed, the drymatter percentage will be lower than typical maize silage (around 22-26%, depending how much moisture is in the stalk and leaves). Depending upon hybrid genetics, a red colour in the lower stem can be a sign of stress due to the inability of the plant to translocate sugars to a normally developing cob.
Table 1 provides a "rule of thumb" or "reference point" for determining whole plant drymatter of drought stressed maize.
Table 1: A decision aid for the timing of harvest in drought stressed maize
|Crop appearance||Small ear due to partial or no pollination||Normal ear development|
|Most leaves have fired (turned brown)
||Harvest immediately||Harvest immediately|
|Green leaves at or above cob||Harvest when green leaf befins to turn brown and DM assessed as above 28%||Assess crop weekly|
|Most leaves are green||Harvest when the stover begins to dry (above 28% DM) to prevent silage run-off (seepage).||Normal harvest but assess crop weekly|
The pictures below were taken of a maize crop grown on a sandy loam soil where less than 13 mm of rain had fallen in the prior six weeks (since flowering). Kernel development had reached milk stage, leaves are rolled and many above the ear are brown resulting in the plants rapidly drying down.
Figure 2: Close-up view of drought stressed maize
Whole plant drymatter = 29.6%. This is the correct stage to commence harvest.
Figure 3: Drought stressed maize silage
This picture represents the visual appearance of the crop from the road. Much of the lower half of the plant is brown. The leaves above the ear are rolled and some are beginning to turn brown (fire). Note moisture levels within such crops will be highly variable so a number of drymatter determinations will need to be made in order to decide on the time to commence harvesting. Drymatter readings from green plants ("grass green") in lower lying areas are illustrative of paddock variability. Green plant drymatter = 25.2%.
ENSILING CHARACTERISTICS AND FEED VALUE
Nutritional composition of drought stressed maize silage
The nutritional composition of drought stressed maize silage is strongly dependent on grain set and development of cobs, which can be reduced significantly when there is a water deficit at the time of pollination. Sugars build up in the green parts of plants with no cob or partly filled cob resulting in nutrients only partly being translocated to the cob and converted to starch.
Silage quality analysis, in drought stressed maize crops in Germany in 1999, showed elevated sugar levels of 15-23% DM (normally 10-15%) and correspondingly low starch concentrations of only 5-20% DM (normally 25-30%). The variation between crops was large, depending on the magnitude of drought damage (Figure 4).
Figure 4: Starch and sugar in crops on nine German farms (Pioneer 1999)
Analysis from East German farms experiencing drought stressed maize silage with little or no ear and strawy stover showed low starch and reduced energy density (15% less than normal crops) as well as a very high drymatter percentage. In crops with little or no ear and green stover it was found that energy density was not reduced as much (10% less than normal crops) due to high sugar levels in the stover. When ears are missing the drymatter percentage is low. Maize with poor ears and green stover usually resulted when there was a water deficit at pollination but subsequent rainfall allowed the plant to recover. Maize with poor cobs and strawy stover did not recover later as a result of on going drought conditions. (See Table 2).
Table 2: Nutritional composition and energy concentration of drought stressed maize silages
|Maize field conditions||Drymatter %||Crude protein
|No or little grain
- stover mainly green
|No or little grain
- stover mainly strawy
(Data from harvest 1994 after Hertwig and Pickert 1999)
Drought can also lead to elevated nitrate levels.
Nitrate is the pre-cursor for plant protein. Nitrate moves rapidly from the soil into the plant and is converted into protein by plant enzymes. The speed of conversion of nitrate to protein is affected by a range of factors including shade, cloudiness, mineral deficiencies and drought. Under drought conditions, nitrate uptake is slowed, but not as much as the loss of enzymatic activity. As a result nitrates tend to build up especially in the lower part of the stem.
Nitrate levels are highest in younger plants because maize nitrogen uptake is about 65-70% completed by the time the plant reaches flowering. The biggest risk of nitrate poisoning occurs when grazing or green-chopping crops prior to flowering. More mature (post-flowering) crops can also have high nitrate levels but the risk is lower.
After rain, nitrate levels fall but only if there is a cob that is a sink for plant protein. Crops that have severe drought stress and no cob development, may still have high nitrate levels even after the drought breaks.
If you are chopping and greenfeeding drought stressed maize, consider lifting the cutter bar to around 30 cm to reduce the amount of nitrate in the harvested material. Contact your local veterinarian to conduct a nitrate test before you feed non-ensiled drought stressed maize.
During the ensiling process 40-60% of nitrate is degraded to gaseous nitrogen products (sometimes referred to as silo gases). Silo gases, which may show as brown to yellow coloured gas emissions under plastic covers are extremely toxic.
Silage quality effects
The silage quality of drought stressed maize depends on the drymatter and sugar level. Strawy stover is difficult to compact and is more prone to heating at feed-out. It is important to chop this material short and compact it well (>230 kg drymatter/m3).
Green maize silage with drymatter lower than 28% tends to produce silage effluent. To reduce the risk of silage run-off and poor fermentation it is recommended that maize silage is harvested above 28% drymatter. When harvesting wet maize silage ask your contractor to lengthen the chop length and turn the plant processor off.
Since the maize plant holds a large amount of moisture in the base of the stem, lifting the cutter bar can also increase the drymatter percentage of the forage that is harvested and decrease the risk of run-off. New Zealand research shows that increasing the cutting height from 100 mm to 600 mm increased maize silage drymatter by 3.4% but also decreased yield by 2.5 tDM/ha.
A high sugar level in low cob percentage maize often leads to high residual sugar in maize silage. Research has shown that this high residual sugar may lead to increased yeast activity and heating during the feeding period.
In both, strawy high drymatter maize silage as well as green low drymatter maize silage, there is a risk of poor fermentation and heating. The best defence against poor fermentation and heating is to follow proper harvest guidelines.
Maize silage harvest guidelines
For more information on harvesting maize silage see Pioneer Technical Insight 302: Harvesting a maize silage crop which is available from www.pioneer.co.nz.
Alternatively phone the Pioneer Advice Line toll-free on 0800 PIONEER (0800 746 633).
Ensiling low drymatter maize silage
Maize silage that is harvested at less than 28% drymatter (around ½ milk-line) can lose a lot of valuable nutrients in the form of silage run-off. Low drymatter silage is also prone to poor quality fermentation. To achieve the best possible results:
- Lengthen the chop length
- Turn the plant processor off
- Use a quality fermentation enhancing silage inoculant such as Pioneer® brand 1132 for short term storage. For longer storage times of more than 30 days use Pioneer® brand 11C33, which helps to prevent heating and mould growth.
- Consider lifting the cutter bar to increase the plant drymatter percentage. (NZ research showed that increasing the cutting height from 100 mm to 600 mm increased maize silage drymatter by 3.4% and decreased yield by 2.5 tDM/ha)
- Compact the stack but don't over roll
- Cover, seal and weigh down the cover with tyres that are touching.
It is generally recommended that maize silage should be harvested at 30-38% whole plant drymatter. However, when there are feed deficits, it may be necessary to start using the maize silage ahead of the normal harvest time by greenfeeding. Maize silage can be greenfed anytime from 6-8 weeks after planting onwards.
Ideally the feed should be precision harvested and carted to the herd. If the crop is drought stressed or very immature, contact your local veterinarian and test crop nitrate levels before feeding.
Deciding when to greenfeed maize silage
It is often difficult to decide whether to greenfeed a maize crop or leave it, especially if the crop is still accumulating yield.
Reduce feed demand
The first management step in dry conditions should be to reduce feed demand. This can be done by:
- Removing genuine culls from the milking herd
- Herd testing and drying off high somatic cell count cows and low producers
- Getting the calves off the milking platform or feeding them meal
- Drying off any young animals in the herd (1st and 2nd calvers) that are in low condition score
- Putting the herd on once-a-day (to reduce stress on cows and farm staff)
Once these options have been taken, attention turns to feeding the rest of the herd. The aim is to milk as many cows as possible for as long as possible without compromising either winter feed supplies or cow condition at calving.
Trials in the mid-1990s at Waimate West showed that very large responses to supplementary feed could be gained if cows which could have been dried off early were kept in milk.
Feed grass and forage crops
Ensure that the herd is on as long a grazing round as possible. If the cows are beginning to leave behind a grazing height of 7 clicks or less then it is likely they are not getting enough grass alone.
Next, feed any crops that have been grown for greenfeed purposes. These will include brassicas and sorghums. Under intense heat conditions brassicas can wilt and lose yield. They should be fed off first. Test for nitrates before starting grazing.
Feed stored feeds
Once it rains the dry grass rots and it takes around three weeks for new grass to grow. It is important to have three weeks of stored feed on hand to feed the herd when it rains. After you have set aside three weeks of feed, look at your other stored feed options.
Grass silage is an excellent alternative for dry conditions. Some farmers may have maize silage left over from the previous season. Maize silage is a great source of energy and is excellent for maintaining cow condition.
If a high proportion of the diet is maize silage, low crude protein levels may negatively affect milk yield. Consider feeding maize silage in conjunction with a protein source such as good quality grass silage or soybean meal.
Consider buying in feed
Depending on time to harvest, maize crops may not have reached their yield potential. In the six weeks prior to harvest, under "normal" conditions, maize silage will accumulate yield at around 200-300 kgDM/ha/day. Greenfeeding early reduces the crop yield and increases the cost per kgDM.
Example 1: A maize silage crop that would have yielded 25 tDM and cost 15 c/kgDM is greenfed at 6 weeks prior to normal harvest time. The greenfeed yields 12.5 tDM/ha and therefore costs 30 c/kgDM.
Consider buying in alternative feeds only if they can be sourced for less than the cost of the greenfeed maize or if there is a lack of protein. Always ensure that three weeks of feed is on hand for when the drought breaks.
As the crop gets closer to harvest, the value of the lost maize yield potential decreases and the case for greenfeeding maize gets stronger. With 15 days to go before harvest, the potential yield loss is only around 3-4 tDM/ha and therefore the cost of that maize reduces to around 18 c/kgDM.
Greenfeed maize is a good source of energy and fibre. Nutritionally it contains lots of sugar and while it is still green, it also has a reasonable amount of protein. This gives it an energy content of around 10 MJME/kgDM and crude protein of between 8-12%
If greenfeeding maize, make sure that the worst crops are used first. These are either currently drought stressed and/or have a low yield potential. Once the paddock has been chosen, there are a number of ways maize can be green-fed.
Grazing in situ
This is the least advisable method as the wastage rate can be high. If there are no other options, feed maize silage behind an electric wire. If the plants have cobs make sure all the cows have access to the crop at once to reduce the risk of acidosis (grain overload).
Cut and carry
If you have your own harvester, cut the maize on a daily basis and cart it to the herd.
If a contractor is required to undertake the harvest, either chop enough maize for several days and leave it in a pile, or stack and ensile enough maize to last until the main crop is ready for harvest. Under normal circumstances, maize silage can be piled and fed for up to a maximum of three days. However watch out for excessive heating and/or mould growth.
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Revised: February 2014
Expires: February 2016