Nutrient Management for Forage Maize
By Mark Scott, Greenmount Campus, CAFRE and Trevor Gilliland, AFBI, Crossnacreevy
Forage maize has been considered by farmers as a ‘hungry’ crop and for this reason land intended for growing the crop has been received both slurry and farmyard manure. In addition, many growers will place inorganic nutrients in the seedbed. This practice can mean in some instances that crops are over supplied with nutrients compared to RB209 recommendations. This article looks at two projects which show that there is no additional gain in yield or quality from the over supply of nutrients to forage maize.
AFBI Research
In addition to conducting the Forage Maize recommended list variety trials, the research team at Crossnacreevy have been investigating the nitrogen requirements of the crop, under local growing conditions.
Contrary to popular belief maize does not have a greater need for nitrogen than other cereal crops. The Crossnacreevy studies have shown that the relationships between soil nitrogen supply, dry matter yield and plant nitrogen concentration in maize are similar to other crops. So, supplying excess nitrogen fertilizer, above plant requirement did not result in higher yields. The work has shown how maize utilises the nitrogen supply as it matures towards 30% starch content. When provided with the correct fertilizer rates the crop will reach a balanced concentration of nitrogen that keeps the plant vigorous and able to achieve its full yield potential but also mature at the required time. The target nitrogen concentration is around 0.9% in the plant tissue. Higher levels of up to 1.2% can be regarded as ‘luxury levels’, and any higher than this is unquestionably excessive.
Current on-farm fertilizer strategies have sought to ensure that maize crops were not nitrogen deficient. Due to the very high yield potential of maize (over 20t/ha DM has been achieved), it has been assumed that very high application levels were essential. For this reason RB209 recommendations have been viewed with a degree of scepticism. The evidence compiled by Crossnacreevy however contradicts this mis-held belief. Crop analysis shows that virtually all the crops had excessive nitrogen concentrations and were significantly above crop requirement. Such excessive fertilizer application represents an unnecessary cost against what is already an expensive crop and may lead to a potential environmental problem. In addition the evidence suggests the plants stay green and their rate of maturing slows leading to later harvesting with the associated problems.
Current RB209 fertiliser guidelines allow for nitrogen application rates of up to 120 KG/ha, but must be take into account the amount of nitrogen in the soil that is available for plant uptake throughout the growing season. The recommended rate for each crop can be calculated from the RB209 guidelines using factors such as the soil type, rainfall, previous cropping history and expected yields.
CAFRE Technology Work
A current CAFRE Technology project looking at several aspects of forage maize was established at Greenmount in 2007 to ensure the best information was available to dairy farmers on the management of the forage maize crop and feeding it to dairy cows. These important aspects of management include:
- Yield and quality achievable
- Sowing date
- Use of plastic
- Nutrient management
- Harvest date
In 2009 the forage maize growing cycle was followed on 10 farms located throughout Northern Ireland. Crop details were fully recorded and analysed from soil analysis through to yields and forage analysis.
Through the recording of soil analysis and nutrient application on the 10 farms it was established that there is no improvement in either yield or quality through the over application of nitrogen (N), phosphate (P) or potash (K) compared to RB209 recommendations. Various amounts of P and K were supplied with the majority of this coming from slurries and farm yard manure. Increasing levels of P and K application did not improve either yield or quality. There was a wide range in the application of N on the monitored crops. As with P and K there was no apparent trend in yield or quality with increasing application rates, in fact the highest yielding crop of the 10 farms had N applied at recommended levels.
The results of this project show that any over application of nutrients above RB209 recommendations will be wasted. In today’s financial and environmental climate this waste is undesirable and uneconomical. The nutrients wasted on this crop would be better utilised by other crops on the farm therefore reducing overall fertiliser bills.
Summary
- CAFRE Technology work and AFBI Crossnacreevy research both clearly agree that by adopting RB209 recommended rates crop yields will not be affected. Indeed farmers can achieve a better economic return, avoid inhibiting the maturing crop and protect against the damaging effects of nitrogen pollution on the environment.
- Nutrient application rates must be calculated from recommendations on an individual basis using information on previous cropping, soil analysis and expected yield
- Always take account of nutrients applied via slurries and farm yard manures before applying inorganic fertiliser
- A simple nutrient application calculator is available by following the links at http://eservices.ruralni.gov.uk/onlineservices/FarmNutrient/FarmNutrient.asp or alternatively DEFRA’s recommendation booklet (RB209) can be used to work out appropriate application rates.
Michael Graham, Greenmount Farm Manager, Mark Scott, Dairying Technologist and Jim Fulton, Assistant Farm Manager observe sowing of the 2010 Greenmount crop on 14 April. 2000 gallons per acre of dairy slurry was ploughed in and the nutrient balance up to RB209 recommendations is supplied via inorganic fertiliser
