In the north of Australia rainfall is reliant on the monsoonal effects to create the main rainfall periods which is from October through to March. Our property has an average rainfall per annum of 896 mm or in the old scale 35.8”.
The pastures we utilise for cattle production are all native grasses they have adapted to grow in the boom and bust of the rainfall occurrences. Relative to the pasture requirements, it is very important to not only receive the volume of rain but to receive it in steady amounts through the hot months of the year to continue that growth and good plant root and leaf establishment.
If rains are received there is a massive growth period of grasses, herbages and trees, if rains stop during very hot periods such as February then a lot of the pasture feeds tends to be dried off and not have the volume and mass level it would have achieved if rains had continued. Their mass of production is deminished as is their seed production capabilities.
In the north when a wet is referred to as a light wet or there have been long periods in between rains then it is often referred to as a poor wet season. The problem is not so much in the initial few months of the dry season, April to September as the feed body is still relatively high enough to allow animal grazing and keep good condition on the animals for weight. The worry for the grazier is the last stages of the dry, when feed loses it protein and nutrient level due to normal haying off. A poor wet means the body of feed is simply not available and drying off starts a few months before it usually would. This makes for a very long dry period in which cattle need to find suitable grazing materials until the next rains come. If the wet season doesn’t arrive until December then the periods of September to the rains can be difficult for the cattle to maintain body condition and health.
Figure 3 – Dry Season- This is a photo (Oct 2013) of a black soil flat with mainly speargrass but also palatable plants of what I think are types of rat tail grasses. This area has cattle on it and while it looks like it has a large body of feed, much of it is either not palatable this time of year or has little nutritional value. Cattle will maintain their condition here for a number of months yet.
In our case the problem was realised several years ago that we were too reliant on natural waters, we had a number of springs and large waterholes that we pumped from to give a clean drink to cattle in the dry season. We weren’t happy with the springs though as the pigs wallowed in them. They still went stagnant to a degree latter in the dry and the water quality simply wasn’t good enough as through the dry their levels sometimes drop. We worried that with a light wet or a particularly long dry season, if the rains were unseasonably late in the year these springs would simply dry up as their surface replenishment had not occurred.
In the 5 years we have been here we have seen two springs that have dried up this dry season, they simply didn’t get the surface replenishment to maintain their flows.
2010/2011 – was a great season, we had light showers in November which was a good start, with really good downfalls in December, these kept up through January ensuring a very heavy soakage of the country, with large volumes of water filling creek systems, at one stage our river peaked at 13.5m. While the rainfall dropped in February it still kept raining and then peaked again in March. This set up a great year for grass growth and high volumes of pasture feed for livestock.
Figure 6.- Wet season – This is our stockyard. A vine grows on it which I don’t know the name of that literally covers our whole yard every year. To clean it up, we just let a few pet cows in and they soon eat it back when fresh and green.
2011/2012 – wet season was OK. It started well in December peaked in January and then dropped to nearly nothing in February. Early in the year is very hot and with young grasses not yet hardened off by the time the March rains came in 2012 many were actually burnt off and had died. The March rain assisted in plant growth but not to the volume of the previous year. The dry season though of 2012 wasn’t too bad as there was enough water and ground moisture to allow good volumes of grass growth.
Figure 7 – Dry Season – Feed that has hayed (dried) off about mid way through the dry season. some of this is speargrass and soft spinifix, not palatable when dry grazing grasses but are important to keep the soil together. Amongst it is some oat grasses and Kangaroo grass which is good fodder.
2012/2013 wet season was pretty lousy wet season. It started very well, In December we received a week of 25mm every day, good steady soaking rain, it was looking to be a great wet season with the ground getting well soaked and grass grown without the massive volumes of water to cause erosion. Then it literally stopped, January and February were shockers for rain, most growth that occurred in December was burnt off by the heat. While we received a saving rain in March and this grew good feed while the weather was still warm. It didn’t have the substantial volume or growth that would mean a late dry season feed coverage was going to be available. Our river barely got above the 5m marker the whole wet which is very unusual and even nearly stopped running in February.
As a comparison of just how poor the 2012/13 wet was, it is the 4th lowest wet season tally received in my records of 39 years. The worst was 1991/1992
Over the last 39 years some huge rainfalls have been recorded
Figure 10- Dry Season – October 2013. This area is on a basalt rock ridge, in the wet it grows very good palatable grasses, because they are preferred by the stock they will graze this area heavily thorugh the dry. This paddock has been destocked now but ideally you wouldn’t want to see the coverage loss any greater through grazing as it would deteriorate its ability to regenerate when there is a rain event.