How Much N Does Your Maize Crop Really Need?
Over the past few weeks, I’ve had several conversations about nitrogen (N) management in maize crops for the coming planting season.
It's not uncommon for farmers to be able to grow maize silage that yields 18-24 tDM/ha for around 25-35c/kgDM in the stack on paddocks that need renewing. Growing costs can be reduced even further by growing maize in an effluent paddock, which can significantly reduce (or in some cases eliminate) fertiliser input requirements.
This drops the cost of maize to 18-25 c/kgDM. That looks pretty attractive compared to buying in alternative feed sources that can range from 50-100 c/kgDM. However, this analysis only tells part of the story when growing maize on farm, and there are other considerations that can influence the return from your maize crop.
First, you need to ask whether the area you want to grow your crop on really needs renovating. The reason for this is that if the paddock is already high producing, the difference in the total extra drymatter production gained by growing maize will be less, increasing the cost per kgDM (Table 1).
Table 1: Value of maize grown on low vs high pasture producing paddocks
| Poor Performing paddock | High performing paddock | ||
| Maize yield | tDM/ha | 20 | 20 |
| Less: Pasture production during maize cropping period | tDM/ha | 4 | 7 |
| Equals: Total extra feed produced | tDM/ha | 16 | 13 |
| Cost to grow and harvest maize silage1 | $/ha | 16 | 13 |
| Cost of additional feed supplied |
Furthermore, you will have missed the long-term opportunity to increase pasture production by renovating the poorest performing paddocks on the farm.
Second, maize growing costs can be reduced significantly if you can grow it on highly fertile effluent paddocks.
Dairy effluent typically has higher concentrations of nitrogen and potassium, which maize can utilise to achieve maximum yields (12kg of N and 10kg of K per 1 tDM maize silage yield). With maize being a deep-rooted crop, it is perfectly suited to utilise this free source of nutrients and reduce the growing costs per kgDM (Table 2).
Table 2: Cost of maize grown on low v high fertility paddocks
| Maize silage yield (tDM/ha in the stack) | |||||||
| Yield | 16 | 18 | 20 | 22 | 24 | 26 | 28 |
| Cost on low fertility paddocks ($kgDM)2 | $0.40 | $0.34 | $0.30 | $0.27 | $0.24 | $0.22 | $0.20 |
| Cost on high fertility paddocks ($kgDM)2 | $0.29 | $0.25 | $0.22 | $0.20 | $0.18 | $0.16 | $0.15 |
Finally, while maize yield and costs are very important, so too is having flexibility around the timing of when you sow and harvest your maize crop.
Consider maize hybrids that suit your environment and the nature of your seasonal feed supply and demand requirements.
For example, being able to sow your crop three weeks later when pasture is growing at 64kg DM/ha/d, equates to 20 tDM of additional pasture silage from 15ha. Alternatively, being able to harvest three weeks earlier could help you to bridge any autumn shortfall of feed you might have normally expected. Talking to your local Pioneer representative will help you establish the best hybrid option for your location and on-farm requirements on farm.
Wade Bell is Genetic Technologies farm systems manager. Contact him at This email address is being protected from spambots. You need JavaScript enabled to view it.
