Better pastures, better crops

Take home messages

• Grass fodders will generally grow more dry matter in a year than legumes and in the vegetative stage their feed quality is equivalent to legumes.
• Most common are the annual legume fodders (balansa, arrowleaf and persian clover) and they can produce significant amounts of high quality fodder under favourable growing conditions.
• Perennial fodders, especially lucerne, will dry the soil profile more than annual fodders. This may compromise subsequent crop yield if seasonal rainfall is below average
• Effective nodulation and husbandry of legumes is critical to achieve nitrogen (N) fixation. Just because a legume grows and looks healthy does not mean it is maximising N fixation
• Controlling seed set, especially in very late season weeds that germinate and grow outside the efficacy of in-crop herbicides is essential to achieve significant and sustained reduction in annual ryegrass.
• Crop yields after a fodder phase may be worse if growing season rainfall is below average because of potential lower starting soil moisture and inability to control the mineralisation of N rich organic matter that can ‘cook’ the crop.

Introduction

The inclusion of a pasture ley phase in a cropping system is not new. A simple computer search reveals pasture ley was at the forefront of farmers and scientists in the 1940s (Roe, 1956), with them grappling with the same issues as we are now around organic matter, fertility and soil structure decline and weeds. Since then new varieties and rotations, advances in chemicals (herbicides, fungicides and insecticides), the adoption of minimum or no till systems along with (until recently) depressed livestock commodity prices has resulted in widespread adoption of ‘continuous cropping’ on many farms.

The pasture ley phase has largely been ignored. yet the issues of weeds, disease, fertility decline, especially N, and to a lesser extent soil structure remain. Data from the recent national soil carbon program through the Volcanic Plains of south west Victoria on similar soil types and rainfall shows a difference in soil carbon, especially the rapid turnover and humic portions of the organic carbon pool under different land uses (Table 1).

Table 1. Total organic carbon (TOC) and organic carbon fractions

In 2012 a GRDC funder project Pastures in Crop Sequencing (SFS00022) explored the opportunities of using a pasture phase in the high rainfall zone to improve crop performance. Fourteen trials and one demonstration were conducted in Victoria and South Australia. The Victorian trials were conducted by Southern Farming Systems and the South Australian trials by MacKillop Farm Management Group and Agriculture KI.

The project examined a range of fodders including variations in sowing rate, phase length and termination practices e.g. spraying, hay cutting, etc. Many parameters were measured including biomass, weed populations, N fixation and subsequent crop yields and quality. Results from individual trials have already been reported (GRDC Grains Research Update Bendigo 2017; Dubbo 2018; Paridaen et al, 2015; SFS final report on GRDC website). This paper aims to summarise the findings under five themes:

1. Dry matter production
2. Grain production after fodders
3. Soil nitrogen
4. Weed control
5. Changes to soil moisture

Results

Dry matter production from fodders

Several factors influenced the total amount of dry matter produced from the fodders sown. Seasonal conditions, species choice, time of sowing and perenniality all had an impact.

A range of fodders were grown across three years (2012 to 2014). During this period the growing season rainfall varied from well above average (decile 8 & 9), to around average (decile 4 & 5) to well below average (decile 1 & 2). As a consequence dry matter production also fluctuated dramatically, with growth more affected by the drier rather than the wetter growing season (Figure 1).

Figure 1. Annual drymatter (t/ha) for a range of fodder species from 2012 to 2014 at Inverleigh – common sowing rate.

A ‘typical’ year was 2012 (roughly average rainfall) and yields were commonly around 7 to 10t/ha for ‘grasses’ (oats and ryegrass) and 1.5 to 6t/ha for legumes. Aerial seeding legumes (arrowleaf, balansa, Persian) were generally higher yielding than sub clover or lucerne.

In 2013 (an above average season), yields for crop varieties sown as a fodder (peas, beans, oats, wheat, vetch) were typically between 10 and 14.5t/ha. Pasture grasses in the same year yielded between 3.3 to 11.1t/ha, but typically around 5 to 8t/ha and legumes between 1.2 and 8t/ha, typically around 5 to 6t/ha. Lucerne was commonly the lowest yielding legume even under favourable growing conditions.

A much drier year was encountered in 2014, resulting in some species failing to establish and lower dry matter production. Perennial grasses such as phalaris and soil seed burial legumes such as sub clover sown the previous year responded more favourably than the annual varieties that required resowing. Pasture grasses that established, commonly yielded between 4 to 9t/ha, with legumes between 1 to 6t/ha. The higher legume dry matter yields were recorded with sub clover and the poorest with established lucerne.

In one trial the ‘weeds’ or nil treatment were allowed to grow (with seed set controlled) and were compared to the dry matter produced by sowing a dedicated species. In 2012, yields from the nil treatment were approximately one third to one half as productive as sown species, however in 2013 (decile 8 or 9) dry matter production was half of the grasses but equal to most legumes.

These results illustrate the range in dry matter production possible from species across different growing conditions. Therefore, the choice of species will depend on the outcomes sought from the fodder phase. These can be summarised as follows:

• For maximum annual dry matter production and grazing consider annual grass species such as oats and annual ryegrass. If a longer fodder phase is sought, consider short-lived perennial ryegrass or phalaris.
• If a legume is required then consider annual aerial seeding varieties such as arrowleaf, balansa or persian clover. If a longer fodder phase is sought, consider subclover however, be prepared for lower growth in the first year.
• If maximum N fixation is required but no grazing, then consider peas or beans.
• Avoid using lucerne in short term rotations as dry matter production was lower than other legume species (and it does affect subsequent crop yields if rainfall is below average).

Fodder quality was consistently high, with digestibility for the legumes throughout the growing season commonly above 75% (10.8MJ ME/kg) and protein above 15%.

Grain production after fodders

An increase in grain production in subsequent crops is a common objective from using a fodder phase. The likelihood of achieving this results is highly dependent on in-season rainfall and the length of the fodder rotation.

One year of fodder

Results from only one year of winter legume (arrowleaf, balansa, Persian, sub clover, peas, beans) showed in most cases no difference in subsequent grain yield of canola or wheat, when the winter crop growing season was favourable (decile, 4, 8 or 9). The exceptions were higher yields at one site after balansa clover or peas. One year of grass fodder resulted in significantly lower yields and could be explained by lower soil N (refer to discussion on soil N).

The second year of crop showed no significant difference in yields from the one year of any species, with the exception of lower yields after oats and serradella. There was no impact on yield of the third crop after the fodder.

Two years of fodder

A two-year fodder phase had an impact on grain yield with most grass fodders (+/- companion legumes) and unsown treatments. Yields were considerably higher compared to treatments that had been fallowed or were in a continuous crop rotation (Table 2). There were no significant differences in protein or screenings.

Table 2. Canola yields in 2014 at Inverleigh after two years of a fodder phase

*Significant differences as indicated by different letter.

Crops sown in 2015 after two years of legume fodder showed a significant reduction in grain yield at the location with decile 1 growing season rainfall but no significant yield loss at the site receiving decile 5 rainfall. This would suggest yield decline following two years of annual legume may occur in very low rainfall years. Both protein and screenings were higher suggesting moisture was limiting.

Three years of fodder

Three years of fodder followed by a crop was only tested with one trial and at two locations. Decile 1 growing season rainfall prevented successful crop establishment at one site (Inverleigh). There were no differences in yield at the other site (Lake Bolac), however yields were well below expectations (approximately 1.2t/ha for canola).

Soil nitrogen

Measuring changes in soil N was challenging, especially given the dry conditions, failed establishment and some crops being ensiled to manage weeds. Most testing was undertaken on a long-term trial, and the two sites at Inverleigh and Lake Bolac showed marked differences in N accumulation under various legumes.

Inverleigh ‘responded’ largely in line with accepted ‘rules’. Total soil N was higher in the legume plots than the grasses and the highest was 17kg/ha of N fixed by Persian clover per tonne of dry matter grown. The accumulated N after two years of fodders resulted in marginally higher canola yields under legumes (except for lucerne) even though it was a decile 2 growing season rainfall. After three years of crop (only 1 year of fodder) there was no difference in barley yields or differences in grain protein, suggesting most of the accumulated N had been used or lost.

In contrast, Lake Bolac did not show increases in total soil N even after three years of legume fodder (Figure 2).

Figure 2. Total soil nitrogen (0-60cm) at Lake Bolac (left) and Inverleigh (right) after two years of Persian clover or annual ryegrass (fodder grown in 2012 and 2013).

Canola yields in the following year from fodder were not significantly different from the common annual legumes such as Arrowleaf, Persian and sub clover compared to the ryegrass. Balansa clover was the exception with significantly greater canola yields after one or two years of fodder. No plant N fixation work was conducted at this site and the fodders appeared visually OK, however there may have been some nodulation issues at the Lake Bolac site that prevented adequate N fixation.

Ongoing work and reports by Belinda Hackney NSW DPI have identified poor nodulation as a major issue in pastures throughout NSW (Hackney et al, 2017) and studies have identified a number of contributing factors including low soil pH, low soil phosphorus (P) and sulphur (S) and already high levels of mineral N (so legumes become ‘lazy’). Residues from herbicides may also be a contributing factor, especially with group B herbicides (Ballard, 2017), despite following the recommended plant back requirements (e.g. Hawthorne, 2007).

The dry conditions no doubt confounded some of the potential yield, and therefore, N response. While yield increases from the legume treatments were only recorded at one location, most showed no significant improvement in yield after the fodder phase. Significant grain protein responses were recorded after one year of legume at several sites but not at others, however screenings were commonly higher under the legume treatments, suggesting inadequate soil moisture limited potential yield.

Weeds

Annual ryegrass and wild radish were the two weeds studied in these trials. Initial weed counts were usually undertaken in July, however ongoing observations illustrate the problem with late germinating weeds, especially annual ryegrass. Mid-crop measurements were not providing an accurate understanding of carry-over weeds. More recent observations were also taken in October and November to pick up very late germinating weeds that had not been controlled by knockdown or in-crop herbicides.

Annual ryegrass

Results clearly show annual ryegrass populations can be dramatically reduced with only one year of a fodder; either a legume, grass or cereal fodder. Achieving adequate seed set control is the key. The only trial where annual ryegrass populations increased was the result of no spring intervention with the fodder treatments. To highlight the importance of seed set control, a canola treatment in the same trial that failed due to waterlogging was sprayed out in spring. This resulted in a dramatic reduction in annual ryegrass the next year compared to the untreated fodders. Increasing the fodder duration from one to two or three years generally had a continuing, albeit smaller benefit in lowering ryegrass populations in the fodders. This also appears to provide greater time with lower plant numbers in subsequent crops.

Other tactics such as increasing crop or fodder sowing rates above common practice and stubble burning proved ineffective in enhancing annual ryegrass control. Delaying sowing time was effective in gaining improved mid-winter weed control however the delay resulted in lower grain yield and no difference in end of season ryegrass numbers because of the late germinating weeds described previously. This confirms the issue of late germinating weeds that are beyond the effectiveness of in-crop herbicides.

Wild radish

Control of wild radish was largely ineffective. While a decline in numbers was observed in the first year of one trial, equivalent or even increased populations of wild radish were recorded, with different fodders or different treatments such as spray-grazing or stubble burning. In one trial the first year of canola after one year of fodder had to be abandoned (crop ensiled) because of very high wild radish numbers. This was irrespective of the treatment applied.

Wild radish was still present in considerable numbers in the first year of crop after three years of fodder. This is not surprising given the longevity of wild radish seed but does bring into question the long-term effectiveness of a short-term fodder phase as a tactic to control this weed.

Other tactics such as increasing crop or fodder sowing rates above common practice, stubble-burning and spray grazing proved ineffective in achieving long term weed control.

Changes to soil moisture

Apart from the lucerne treatment, most annual fodder species dried the soil profile by a similar amount. With adequate winter rainfall in 2013, the soil profile was full (sometimes waterlogged) by the end of winter and the water used by various fodders in that year was similar. Crops grown in the 2013 year showed no yield difference that could be related to differences in starting soil moisture created by the previous fodder.

2014 was a dry year and starting soil moisture after two years of fodder were the same between Persian clover, sown ryegrass and the nil treatment (% w/w of 39%, 38% and 42% respectively). There was no significant grain yield difference between treatments.

The exception was in 2015 at Frances in South Australia, where there were differences in starting soil moisture due to the treatments and a strong correlation with grain yield. In this trial the lowest soil moisture was under lucerne, followed by the grasses (perennial ryegrass and phalaris). Highest soil moisture was under crop fodders (oats for hay, peas for green manuring) and a fallow treatment and this correlated with higher grain yield.

Similar differences in soil moisture between fodder treatments were not measured at other sites.

This data shows that perennial fodders such as lucerne, phalaris and perennial ryegrass are likely to deplete soil moisture from the profile more than any of the annual fodders (annual clovers, annual ryegrass) but less than crop species such as oats or peas sown for fodder or green manuring and then terminated before the end of the growing season. Adequate growing season rain is required to avoid compromising subsequent grain yield because of the extra moisture depletion.

References

Ballard R (2017). Strategies to improve N2 fixation by sub-clover and lucerne. 58th Annual conference of the Grasslands Society of Southern Australia.

Hackney B, Jenkins J, Powells J, Edwards C, Orgill S, DeMeyer S, Edwards T, HowiesonJ, Yates R (2017). Nodules or not – a survey of pasture legume nodulation in central and southern NSW. Proceedings of the 2017 Agronomy Australia Conference, 24 – 28 September 2017, Ballarat, Australia.

Hawthorne, W (2007). Residual herbicides and weed control. Pulse Southern Pulse Bulletin PA 2007#03. Pulse Australia.

Paridaen A, Celestina C, Vague A, Falkiner S, Watson D, Nicholson C (2015) Adding value through pasture and fodder break crops - is the current break crop broken? Proceedings of the 17th ASA Conference, 20 – 24 September 2015, Hobart, Australia.

Roe R (1956). Ley farming. CSIRO Armidale

Acknowledgements

The findings in this paper are the result of many years of research and investigation by a lot of people involved in the Pastures in Crop sequencing (SFS 00022) and Grain and Graze (SFS00028) programs from 2008 to 2016. There are too many people to mention. However, the program would not have been possible without the significant and ongoing contributions of growers through the long-term support of the GRDC.

Contact details

Cam Nicholson
Nicon Rural Services
32 Stevens Street, Queenscliff, Vic 3225
0417 311 098
cam@niconrural.com.au