Cool season production of tropical grasses

Arthur Cameron, Principal Pastures Agronomist, Darwin

There is interest in growing fodder under irrigation during the Top End Dry Season to supply live cattle export yards and cubing/pelleting plants with hay.

Tropical grasses generally do not grow well under irrigation during the cooler months of the year in the Top End of the Northern Territory. Sugargraze Forage sorghum (Sorghum sp) and Finecut Rhodes grass (Chloris gayana) have been shown to produce commercial yields of 25 to 35 tonnes per hectare per year at Douglas Daly Research Farm (DDRF). Both of these options for fodder production under irrigation have limitations. The Forage sorghum generally needs to be resown every year to maintain a productive stand. In the Top End, the Finecut Rhodes grass is not liked by cattle as a fodder, and it has a high tensile strength, which makes it difficult to grind and make into fodder cubes and pellets.

There are a number of other tropical grasses which have cold tolerance, and may be suitable as alternatives to Forage sorghum and Finecut Rhodes. The cool season growth of seven other tropical grasses is being compared with that of Finecut Rhodes at Coastal Plains Research Farm (CPRF) to select one or more cultivars which have equivalent or better cool season growth and/or better acceptance by cattle and better grinding characteristics.

Seven of the grasses were sown by seed in December 2014. The eighth grass, Strickland Finger grass, was planted by runners in February 2015. The grasses planted and the first year’s yield results are presented in Table 1 (below). The establishment was good except for the Premier Digit grass which was attacked by Crab grass leaf beetle larvae. While Strickland finger grass and Premier digit yields were lower overall, the yields were similar for all of the grasses at the final harvest

The trail continued this year to get a full dry season’s results. Samples from each harvest will be submitted for nutrient and quality analysis.

GrassDM kg/ha (2015)Total DM Kg/ha
6 May25 Jun11 Aug29 Sep17 Nov
Finecut Rhodes 5980 5500 3000 6900 7080 28450
Gulfcut Rhodes 6980 4720 2690 7350 6990 28720
Reclaimer Rhodes 7730 4990 2850 6570 7500 29640
Premier digit 940 1540 2110 4940 7120 16640
Strickland finger grass 4690 4360 2450* 6030 6770 24370
Gatton panic 7340 6510 2230 4930 6340 27350
Nucal panic 8980 4630 3590 6538 7880 31320
Splenda setaria 9280 5870 2290 6210 6320 29980
Mean 6490 4760 2660 6180 7000 27100

Table 1. First year yield results. *Strickland finger grass yield was decreased by selective grazing by wallabies prior to the 11 August harvest

The plots were cut and cleared off on 23 February 2016, then fertilised. The irrigation was turned on to water the fertiliser in, and left turned on because of the low rainfall wet season. Results to date for 2016 are presented in Table 2 (below).

Grass

DM kg/ha (2016)

Total DM Kg/ha

6 April

31 May

26 July

13 Sep

25 Oct

Finecut Rhodes

3850

4520

5800

6500

2480

23140

Gulfcut Rhodes

3590

4990

6830

5950

1830

23190

Reclaimer Rhodes

4060

5120

6280

6730

2280

24470

Premier digit

4110

3130

3240

3820

4040

18330

Strickland finger grass

4790

3710

3820

4270

3520

20110

Gatton panic

4370

3950

3910

4180

2840

19250

Nucal panic

6380

4020

4780

5630

6150

26950

Splenda setaria

2720*

4920

4910

3620

4370

20550

Mean

4230

4300

4950

5090

3440

22000

Table 2. Second year yield results.  *Splenda setaria yield was reduced because it was set back when the plots were sprayed for broadleaf control with metsulfuron methyl/2,4-D amine

At the clearing cut, the site was dry. Nucal clearly had the best yield, estimated at 5 tonnes/ha, with the rest about the same yield except for the 2 Digitarias, which were slightly lower.

The Rhodes grasses lost an estimated 10 to 15% of plants following this clearing cut. There was no apparent mortality in the other five grasses.

Please note that the dry matter yields presented here are at 0% moisture. Hay generally is about 12% moisture, so hay yields would be that much higher.

One of the impressive Nucal plots at Central Plains Research Farm on 26 October 2016

One of the impressive Nucal plots at Central Plains Research Farm on 26 October 2016

At the harvest on 13 September, some of the grasses were displaying symptoms of potassium deficiency, so the potassium application for the final period was doubled.

At the final harvest it was noticeable that the plant populations in most of the Rhodes grass plots and in the Gatton panic had declined. This is reflected in the yields from the final harvest.

The two-year total yield is presented in the Table 3 (below).

Grass

Total DM 2015

Kg/ha

Total DM 2016

Kg/ha

Total DM over both years

Kg/ha

Finecut Rhodes

28450

23140

51600

Gulfcut Rhodes

28720

23190

51900

Reclaimer Rhodes

29640

24470

54100

Premier digit

16640

18330

34970

Strickland finger grass

24370

20110

44480

Gatton panic

27350

19250

46600

Nucal panic

31320

26950

58570

Splenda setaria

29980

20550

50530

Mean

27100

22000

49100


Table 3. Total yield over the two years.

Overall, the yields of all the grasses were satisfactory. The annual yield for 2016 was five tonnes lower than 2015. This was because the first cut in 2016 was only a clearing cut, as the trial was not fertilised but managed to produce a hay cut by February. The highest yield was Nucal panic at 58 tonnes followed by Reclaimer Rhodes at 54 tonnes.

Last updated: 19 December 2016