While phosphorus has long been the lynchpin for pasture and livestock production in Western Australia, its status as most limiting nutrient is fading behind decades of application. Now other nutrients are more likely to limit production.
Nitrogen is one nutrient that could now be the most limiting nutrient for many high rainfall livestock industry enterprises. For most, fertiliser nitrogen is typically applied once per year to hay crops and not at all on other paddocks. Nitrogen can also come from legumes such as sub clover (if nodulating adequately) and the breakdown of soil organic matter, and this may be adequate for farms with low stocking rates. However, those with higher stocking rates need to produce enough quality fodder to get through the feed gap, which seems to be getting longer with a drying climate and late starts to the season. Also, a surplus of fodder can allow early season deferral of grazing so pastures can establish adequately at a time when growth rates are low and the risk of over-grazing is high. While there are many factors that contribute to quality fodder production, adequate nutrition is critical.
One producer interested in seeing whether better nitrogen management can improve fodder production and sustainability in a drying climate is Nannup beef producer Mark Scott.
“We’ve been suspicious over the past few years that nitrogen has been our limiting factor for fodder production across the farm. We’ve been rotationally grazing but haven’t been getting what we consider to be the full benefit, particularly in August when we tended to struggle to provide enough feed during the feed gap when it got cold. And we weren’t getting good establishment of pasture early in the season.”
By process of elimination, Mark decided that nitrogen might be a key limiting factor in production. However, he wasn’t sure how to best manage nitrogen or whether there would be a significant response to using more regular applications of nitrogen through the season compared to one or two in spring.
In 2019, Mark found support from South West Catchments Council, who helped design and monitor a replicated trial comparing yield response from different nitrogen regimes. The treatments included:
- Four applications of urea at 80 kg per hectare (equivalent to 37 kg of nitrogen per hectare) at early June (pre-grazing) and again after each graze in late June, July and August
- A single late August application and
- A nil-nitrogen treatment.
“The trial showed us that we could get a really good response from more regular applications of nitrogen. We did four pasture cuts per treatment (one per plot) and estimated a hay yield of 6.8 tonnes of dry matter per hectare compared to 3.8 tonnes for the spring nitrogen and 3 tonnes for the nil.”
The nitrogen trial was monitored with a drone 5 times between July and November. The above photo was taken the day before hay cut on 21 October and when pasture biomass was sampled. (HN = high N rate, N = 4 applications through year; S/N = single spring application; and Nil = no nitrogen.
Mark also applied a similar fertiliser regime to the remainder of the paddock and said his hay yield averaged just under six tonnes per hectare.
“It has cost a lot, but we estimated that we produced a minimum of ten tonnes for the year in grazing and hay. That’s about $70 per tonne of dry matter which I think is a pretty reasonable figure.”
The key to the practice is to have a systems approach.
“We soil tested to begin with, applied basal fertilisers of phosphorus and sulfur at the trial site and also potassium outside of the trial area as recommended by soil tests. We also applied appropriate lime. We seeded 20kg of ryegrass and 5kg sub clover with a seeder rather than aerial seeding which we were doing because the farm is hilly, and that seeding helped incorporate the lime into the ground. After germination we controlled insects. Then we’ve applied nitrogen in early June before the first grazing because the paddock was late in the rotation, and then nitrogen applications consistently after each grazing. We also tissue tested later in the season.
“I’m a little bit suspicious that if you leave any one of those elements out of the system or you don’t do it properly you won’t actually get a good response.
One of the key factors in making nitrogen profitable is to ensure the increased pasture growth is utilised by stock and not wasted. That is where a well-managed rotational grazing system can help.
“The rotational grazing is a big part of it. In the trial area the first graze was only for half a day (200 cows in 6.5ha), so we didn’t put a lot of pressure on it and let it establish properly. We started grazing late (June 19) and our first rotation through June was 32 days and then 36 days in July and August with a 21-day rotation in spring on non-hay paddocks. This helps to maximise utilisation.
“Part of the system is that if we are putting on nitrogen, we’ve got to be aware of what form the nitrogen is and what its acidifying capacity is. If we’re adding nitrogen, we’ve got to add lime to counterbalance soil pH.
“We’ll definitely carry on with the system next year. The only thing we might change is that some of the tissue tests have come back a bit short in zinc. So, we will investigate putting zinc on with the basal fertiliser and also as a foliage spray when we spray for mite. I think also with high levels of nitrogen and high levels of production we will start to hit other limitations so need to keep testing. We will also use lime and gypsum again at 2t/ha, and next seeding we will drop clover and just use 30 kg of straight ryegrass. The reason is that we aren’t getting good clover establishment and it’s expensive to buy. Until we get a better soil balance and establishment, ryegrass will give us a better return, especially with our high stocking rates.
“The system winds up because you produce more fodder to fill the feed gap and that allows you to defer grazing more at the start of the season and let the pastures establish roots and become more productive through the year. Ultimately that helps secure us in a drying climate. If we can produce enough fodder on farm to protect us from those late starts, then it makes us a more sustainable business even with a drying climate.”
This project is supported by South West Catchments Council, through funding from the Australian Government’s National Landcare Program and Western Beef Association Inc.
