Queensland Department of Agriculture and Fisheries senior research agronomist Darren Aisthorpe was one of the researchers who visited Biloela and Emerald recently to discuss trial data from the northern farming systems project.

CENTRAL Queensland growers may need to critically assess their farming practices if they are to remain profitable and productive in the future.

With issues such as soil fertility decline, increasing soil-borne pathogens and herbicide resistant weeds posing a challenge for many farming operations, growers are beginning to query whether their current farming systems will be sustainable over the long-term without a strategic `rethink’ of crop sequencing, crop intensity and nutrient inputs.

Over the past five years, the Grains Research and Development Corporation (GRDC), Queensland Department of Agriculture and Fisheries (DAF), CSIRO and New South Wales Department of Primary Industries (NSW DPI) have invested in a flagship northern farming systems project that is investigating whether system performance can be improved by modifying the farming system.

The project includes six regional sites stretching from central Queensland to central west NSW and a larger site at Pampas on the eastern Darling Downs, while an additional four sites were added in 2017 as part of a southern NSW-focused project.

These regional sites are comparing a set of five to eight system modifications to the local baseline farming system, while the Pampas site is comparing 38 different systems, which vary in their crop intensity (the number of crops sown/year), the use of break crops and/or legumes, and nutrient supply strategy.

At Emerald, the farming systems being investigated are:

• Baseline – a conservative zero tillage system targeting one crop per year. The crops include wheat, chickpea and sorghum with nitrogen (N) and phosphorus (P) rates on cereals targeting median seasonal yield potential.
• Higher legume – an increased frequency of pulses (that is, one pulse every two years) to assess the impact of more legumes on profitability, soil fertility, disease and weeds, with N and P rates on cereals targeting median seasonal yield potential.
• Higher crop intensity – increased crop intensity to 1.5 crops per year when water allows. Crops include wheat, chickpea, sorghum, mungbean and forage crops/legumes with N and P rates on cereals targeting median seasonal yield potential.
• Higher nutrient supply – examining the economic and agronomic implications of increased N and P rates targeting 90 per cent of yield potential based on soil moisture in a variable climate environment. Crops and other practices are the same as the baseline system.
• Higher soil fertility – repeats the higher nutrient supply system but with the addition of 60 tonnes per hectare of manure. This treatment was designed to see if higher initial soil fertility could be maintained with greater N and P inputs targeting 90 per cent of yield potential based on soil moisture.
• Integrated weed management – This minimum tillage system is focused on one crop/year but employs a wide range of practices to reduce the reliance on traditional knockdown herbicides in central Queensland farming systems. Crops include wheat, chickpea, sorghum and mungbean.

QDAF senior research agronomist Darren Aisthorpe said the project was initiated in response to industry analysis’ showing that only around 30pc of northern crop sequences are achieving 80pc of their water use efficiency, suggesting system efficiency could be significantly increased in many instances.

“In combination with emerging farming challenges with fertility, weed and pest management, there is a recognition within industry that modifications are required to maintain the productivity of farming systems,” he said.

“Growers, consultants and researchers from across the northern region were consulted in the project design to ensure it addressed the major challenges being experienced in the different regional production areas.

“The research assesses six distinct farming systems however we realise that over time, many growers may use a combination of several within their farming operations.

“As researchers, we understand that growers are primarily concerned with maintaining gross margin returns and the practicality of modifying or introducing new practices to achieve this.

“The purpose of separating out individual farming systems enables us to make useful comparisons as to their individual contribution to productivity, profitability and soil health.”

Now into the fifth year of trials, Mr Aisthorpe said the six systems were beginning to show differences due to modifications in the crop rotation, nutrition and agronomic management.

“Some of the take-home messages to date are that crop intensity is the biggest driver of system productivity and getting it wrong had the biggest impact on profitability across the northern region – $200 to $700/hectare/year,” he said.

“At Emerald, higher crop intensities had higher productivity but not higher profitability while lower crop intensities had lower costs and a higher return on investment per crop, which is certainly more favourable under drier conditions.

“Higher legume frequency had similar profitability but with higher costs – there were very few savings in fertiliser inputs as the nutritional requirements of the crop put an increased draw on the available nutrition in the soil, relative to the baseline system.

“Crop diversity had variable results across the regional trial site locations but what was evident was that there’s merit in using a benchmark of $2.50 gross income/millimetre of rainfall as a measure of system effectiveness or efficiency in converting rainfall into income over a prolonged period.”

Some of the central Queensland implications for growers in the findings included:

• The baseline system slipped behind most systems on most indices, showing a conservative nutrient approach many not be ideal for central Queensland.
• The higher legume system benefited significantly from the two chickpea crops in 2015 and 2018.
• The manure applied in the higher soil fertility system has resulted in the system leading in most indices.
• The integrated weed management system has produced the highest amount of plant material as a direct result of the higher target plant populations and improved establishment from the narrower row spacing.

In this system, yield response has been good to date because of the improved populations; however, it has not been able to match the higher nutrient, legume or fertility treatments. Using only an `average yield’ nutrition program, nutritional demand for the system may begin to exceed any water limitations, resulting in compromised yields, particularly in high yield potential seasons.

Regardless, the higher biomass should result in higher organic matter levels over time.

• From a sustainability point of view, only the higher nutrient supply system is holding ground with respect to nutrient rundown.
• All other treatments except higher soil fertility are seeing declines in soil P, N and organic carbon.

“This work has raised a number of questions, particularly about the sustainability of both the higher legume system because of the nutrient removal of the grain, but also the integrated weed management system with the significantly higher biomass productions for no extra grain to date.”

Source: GRDC

Contact Darren Aisthorpe , DAF Emerald or to download a copy of a recent GRDC Update paper on the project click here