Sorghum vs maize

16 Oct, 2017 08:47 AM
It is critical for farmers to understand feed gaps both in terms of timing and nutritional value...

Sorghum and maize can each play a part in providing home-grown feed on dairy farms but farmers need to carefully prepare and follow a plan to obtain the most value from these crops.

Murray Dairy through its Accelerating Change project has run a series of workshops to help farmers understand the keys to success if they are thinking about growing maize and/or sorghum.

The Accelerating Change project aims to support farmers to develop profitable and resilient businesses through driving feedbase and irrigation management efficiencies

Three summer crop workshops were run by Murray Dairy, and included presentations and demonstrations from Landmark cropping agronomist Matt Nihill, soil scientist Christian Bannan, Lallemand silage consultant David Lewis and Murray Dairy extension officer Lisa Birrell. The workshops covered the agronomic, ensiling, financial and nutritional considerations of growing a good crop and effectively utilising the feed.

When evaluating whether summer crops are a good fit within a dairy feedbase system, the main factors farmers need to consider are:

What feed gap the crop would fill.

  • The cost:benefit analysis of the crop by looking at yield, nutritive value and inputs including water and fertiliser requirements.
  • The infrastructure available to grow, store and feed the crop.
  • The skills and capability available to each farm to support growing each crop.
  • Murray Dairy extension officer Lisa Birrell said it was critical for farmers to understand feed gaps both in terms of timing and nutritional value and what they wanted out of the forage type.

    If farmers were chasing a feed gap in autumn and wanting to bulk out autumn pasture, then maize silage was an excellent option. However, if they had a feed gap in summer or were looking for something to replace a perennial pasture over summer then they could directly graze sorghum, which minimised the capital infrastructure needed and also directly substituted pasture in the rotation.

    Sorghum could be conserved as silage in a bale, however nutritive value was quite low compared with the more traditional summer fodder crops such lucerne, and ensiling must occur at the same time as optimal grazing to maximise quality, Ms Birrell said.

    Mr Nihill said to get the best results from summer cropping, it was vital farmers understood the commitment and outlay required to achieve high yields with both crops. He likened growing maize to baking a cake - the recipe needs to be followed to the letter to achieve the best outcome. This included preparation, site selection and sowing, in-crop management, harvest, storing and feed-out.

    In the second workshop of the series, an on-farm tour in the Riverina looked at the impact of subsoil constraints on maize performance. A key outcome of the day was that correctly identifying and diagnosing soil constraints was critical to ensure that agronomic management would be effective at fixing any limiting factors.

    This is important to consider when selecting sites to grow maize to ensure that preparation is suitable, as many soil constraints cannot be addressed once the crop is up and growing. For example, would the site respond to deep ripping to allow better water infiltration? Is it acidic or alkaline? Is lime or gypsum needed and what is the weed pressure like?

    "If there has been a history of summer grasses, potentially look at another paddock option because it is hard to control those in sorghum or maize," Mr Nihill said. It could also be difficult to grow these crops on pugged pasture paddocks, particularly if they had previously been susceptible to summer grass weeds.

    "If it is pugged alone, we could work on doing some sort of cultivation," Mr Nihill said. "If there is a history of grasses, then certainly I would look at getting good control over this summer in preparation for a summer crop in the following summer.

    "That's not to stop you from putting a winter crop in between time but the grasses that want to grow over the summer need to be controlled over summer."

    Growing maize

    Mr Nihill said maize was a rewarding crop to grow but the following factors were vital:

  • The paddock was well prepared.
  • The farm business was prepared to invest adequately, both financially and with attention to detail.
  • All critical stages - sowing, watering, fertilising and harvesting/ensiling - were done at the correct time.
  • Advice was sought from other growers and agronomists with expertise in maize growing.
  • The farm could work effectively with contractors.
  • The farm had the infrastructure to feed out with minimal wastage - including silage storage facilities.
  • Maize could provide a low-protein top-up feed when the herd was grazing autumn pasture. It might still need some effective fibre (scratch factor) but that depended on chop length.

    Ms Birrell said maize was fantastic for putting on some body condition, particularly around joining time or in late lactation or for dry cows. It was advantageous in that it did not present the same acidosis risk as grain.

    Maize typically provides about 11 megajoules of metabolisable energy (ME) per kilogram of dry matter, with crude protein levels of about 7-8 per cent and neutral detergent fibre level of about 40 per cent.

    Mr Nihill said it was vital to select the right paddock and prepare it correctly. Factors to consider in selecting the paddock were whether adequate irrigation water was available for flood irrigation, how long it would take for water to drain from the paddock, how much weed pressure there was in the paddock and the soil structure and fertility.

    The ideal paddock was one that took between four and eight hours to flood irrigate and drain, with anything up to 12 hours still acceptable. In paddocks that took between 12 and 18 hours to irrigate, the crops should be planted in beds, while paddocks that took longer than 18 hours should not be considered for maize. This was because maize was not tolerant of water logging, particularly in the establishment phase.

    Mr Nihill said farmers needed to be prepared to spend time and dollars on combatting potential weeds. If the paddock was prone to summer annuals and couch grass, it would be better to prepare it over two years.

    Soil testing well before planting was important to determine limitations in the soil. Critical major nutrients were phosphorus, nitrogen and potassium as well as the micronutrient zinc.

    Table 1 shows the weekly requirements for maize for key nutrients and water.

    If nitrogen application was split, at least 50 per cent (200-300 kg/ha urea) should be generally pre-drilled, placed at least 5 centimetres below the seed so as to not contact the seed. The remaining 50 per cent should be applied by the end of silking (week 10).

    Another option for soils that were not sandy or light was to apply all the nitrogen pre-sowing in a deep band at least 25cm below the seed.

    All phosphorus should be applied at or before sowing. Ideally, place DAP 5cm below and 5cm to the side of seed row. Colwell P levels should be above 90 ppm before considering a reduced fertiliser rate.

    Maize required high levels of potassium, which should be applied before planting if soil testing or paddock history indicated this was required. Deficiencies might occur in silage and hay crops where removal was high.

    Mr Nihill said maize was susceptible to zinc deficiency, which could be a reason why crops did not respond to N applications as expected. Zinc was rarely deficient where manure had been applied recently. Farmers should tissue test to be sure as soil tests weren't always reliable in predicting crop response to zinc fertiliser. A zinc deficiency could be remedied with a foliar spray.

    A liquid starter fertiliser, also known as Pop Up, which contains N, P and Zn, could be applied close to the seed. This could be particularly beneficial for early plantings where nutrients such as phosphorus and zinc were less available. In turn, this could increase seedling emergence and early vigour.

    When planting, farmers should prepare the paddock to make it easy for a precision planter to be used.

    They should seek advice when selecting a hybrid - looking for one with a suitable comparative relative maturity (CRM) to suit the season, taking into consideration that longer CRMs could increase yield potential for silage, but would mature later, which lengthened the harvest window and implicated timely sowing of the following crop. It was also important to ensure the planting population was correct, generally 80,000 to 95,000 seeds per hectare.

    Mr Nihill said achieving a weed-free crop started well before the crop was to be sown. Weeds competed with maize for moisture, sunlight and nutrients. Use a knockdown, even in low weed numbers, and use a post-sowing pre-emergent (PSPE) if necessary. There were limited pre-emergent and post-emergent herbicide options with maize so farmers might consider inter-row cultivation or shielded sprayer in the first 3-4 weeks if chemicals were not effective.

    The main insect pests of maize were wireworm, cutworm and heliothis. Using a seed treated with imidacloprid could help with wireworm, but it was vital growers knew the paddock history and monitored crops for these pests.

    Mr Nihill said water management was vital in maize crops. It was a big determinant of yield.

    Farmers should be aware of the critical stages for water demand and should keep well ahead of these. A moisture probe could be useful to plan ahead for water requirements.

    Growing sorghum

    Mr Nihill said sorghum could provide a good fit for a farm looking to fill a summer feed gap or where paddocks needed to be renovated due to pugging or weeds. It could be conserved as hay or silage to be fed as part of a ration for dry cows, but not as a standalone feed, and it was lower value than maize silage.

    Sorghum typically provides about 8-11 MJ ME/kg of DM, with crude protein levels of about 7-18 per cent (although not all the protein is digestible and therefore accessible to the cow) and NDF level of 50-65 per cent. The quality declines quickly once it was past the ideal grazing height.

    Ms Birrell said farmers also needed to be aware of the animal health risks of grazing sorghum, particularly prussic acid and nitrate poisoning. Prussic acid poisoning was not readily treatable and levels increased in hot, humid conditions or if sorghum crops were stressed.

    Mr Nihill said agronomically, forage sorghum could be more forgiving than maize. It was still vital to be prepared and invest in key areas including paddock preparation, sowing, nutrient management and pest and weed control.

    The main nutrient requirements of sorghum were P and N. Typical fertiliser rates for irrigated crops were 150 kg/ha DAP at sowing and 100 kg/ha urea, applied both pre-drilled and top dressed.

    "Certainly one of the issues to consider is keeping nitrogen up to the sorghum," Mr Nihill said. "When you are removing that sorghum through grazing of fodder conservation, you are also removing nitrogen, so to get the sorghum to reshoot and grow - whether that be cutting or grazing - it is certainly a good idea (to apply nitrogen)."

    The main weeds to control were broadleaf weeds once the crop had emerged. Grass weeds needed to be controlled before sowing.

    Mr Nihill said pre-irrigation watering was the preferred option. Water was also a limiting factor for yield for sorghum, which did not necessarily use less water than maize.

    Like maize, sorghum variety selection was also important.

    Sorghum-sudangrass hybrids offered good cold tolerance, quick growth and recovery, intensive production suited to dairy cattle, high feed quality and could also be used for silage or hay production.

    Sudan x Sudan varieties could only be planted when soil temperature had reached 16 degrees Celsius and was rising. They offered fast growth and regrowth, had a prolific tillering habit, had superfine stems and were super sweet and leafy. These varieties produced higher quality hay, were highly palatable at all stages of maturity and had low prussic acid levels.

    Mr Nihill said grazing management was critical. The aim should be to graze when the crops was between 60 centimetres and a metre to reduce the risk of prussic acid and optimise quality.

    It was also important to keep on top of grazing. If the height became out of control, quality was lost. Ensiling at this stage would not improve quality.

    The Accelerating Change project is also looking at the fit of winter cereals in dairy feedbase systems and how to increase return on investment in these crops by improving agronomic management. D

    For more information on summer and winter crops, and how to improve them on farm, visit the Accelerating Change website

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    Carlene Dowie

    Carlene Dowie

    is editor of Australian Dairyfarmer magazine


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