Dr Jian Jin is a problem solver who is particularly drawn to understanding mechanisms in new farming systems that have potential to improve grain production.

His GRDC-supported postdoctoral research began in 2016 as part of a project to understand the amelioration processes for subsoil application of organic and other amendments in the southern region.

The researcher was supervised by Agriculture Victoria researcher Professor Roger Armstrong at Horsham. Dr Jin’s role was to show how subsoil amelioration treatments were able to deliver changes in soil physical properties, root growth, canopy development and crop yield.

Equipped with a degree in agronomy from Northeast Agricultural University, China, Dr Jin completed a PhD in 2016 at La Trobe University, studying soil carbon and nutrient cycling, plant nutrition, crop physiology and agronomy.

“I am keen to conduct research that improves understanding of the nature of practical problems and provides integrated solutions in the fields of soil management, crop physiology and agronomy,” he says.

Dissecting responses to amelioration

Dr Jin took crop and soil measurements on four selected treatments at two of the Victorian experimental sites where dense sodic clay subsoils are a major constraint to crops: Tatyoon in the high-rainfall zone, and Kiata in the medium-rainfall zone.

The objective was to understand how subsoil amelioration treatments deliver changes in soil properties, root exploration, crop water use, the development of the crop canopy and biomass, and grain yield, under different rainfall regimes.

The four treatments in Dr Jin’s study were only applied at the start of the experiments in 2018, and included (1) an unamended control, (2) 10 tonnes per hectare of gypsum placed at 20 to 30 centimetre depth, (3) chicken manure added to topsoil, and (4) chicken manure added at 20 to 30cm depth. Chicken manure pellets were applied at 20t/ha at the Tatyoon site and 15t/ha at the drier Kiata site.

Both sites experienced two dry seasons with dry springs followed by a wetter year. At Tatyoon, the annual rainfall was 436, 442 and 557 millimetres for 2018, 2019 and 2020, respectively. At Kiata, the corresponding annual rainfall was 249, 225 and 430mm.

At the Tatyoon site in 2018, the manure-subsoil application resulted in 8.1t/ha of wheat, 23 per cent above the control yield of 6.6t/ha. However, in 2019 and 2020 when barley and faba beans were grown, the mean yield increases with the subsoil manure of 0.3 and 0.2t/ha, respectively, were not statistically different to the control. Yields in the surrounding paddock were similar to those in the control treatment.

At the drier Kiata site, there were no significant increases in grain yield compared to the control in 2018 and 2019, in part reflecting the dry seasonal conditions (decile 1 to 3).

Dr Jin says the deep banding of manure at the wetter Tatyoon site had positive effects on the soil, including an increase in rainfall infiltration into the subsoil. This could potentially minimise the development of perched water tables (causing waterlogging),which are quite common on sodic clay subsoils in this region.

Root growth increased in the soil around the subsoil manure, which was associated with increased crop water use. Consistent increases in crop canopy photosynthesis, transpiration efficiency and green leaf duration were observed with the manure amendment.

However, these benefits failed to deliver crop yield increases in the second and third years of the trial.

We think this may be due to the subsoil constraints at Tatyoon not being severe enough to limit crop yields in these years when the crop was less reliant on subsoil moisture in spring.

Although opportunities to meet face to face were restricted by COVID-19 in 2020, Dr Jin has benefited greatly from Professor Armstrong’s supervision and interaction with the wider research team across four states.

“Designing resilient cropping systems and understanding the drivers of these systems is going to be imperative for growers to maintain profitability as we experience climate change and I am keen to focus my future research on these issues for the benefit of the Australian industry.”

More information: Dr Jian Jin, 0406 091 227, j.jin@latrobe.edu.au