Summary

Trials showed that on-row sowing benefits are mainly attributed to lower levels of surface salts in the soil at the on-row position. Both lentil and barley recorded significant yield gains associated with on-row sowing compared to inter-row in both seasons which translated to large partial gross margin returns. Soil surveys across coastal areas of YP demonstrated that approximately 40 per cent of paddock zones would benefit from on-row sowing.

Background

Yield benefits have been reported with on or near row sowing in coastal areas of Yorke Peninsula. The mechanisms behind improved early crop vigour that lead to increased grain yield were not well understood.

Research Aims

The core objectives of the project were to:

• Demonstrate yield benefits from on or near row sowing of previous crop stubble lines under different phosphorus management programs through replicated trials.
• Use on-farm demonstration trials to assess variations in soil type within paddocks.
• Survey soil conditions for 2022 on-row sowing vs near row sowing.

In The Field

Replicated trials were conducted at Anna Binna, a moderately saline site and Thiepvale, a highly saline site across two seasons to assess the response of barley and lentil to phosphorus applied with the seed in the on-row or inter-row position.

Soil surveys were conducted in 50 paddocks prior to the 2022 growing season, primarily along the western and eastern coasts of YP. Samples were taken either on previous year’s sowing lines or in the inter-row at a depth of 0-10cm and fully characterised.

Demonstration sites were established in 2022 and 2023 where growers were encouraged to run strips of crop sown in previous stubble lines adjacent to crops sown in the inter-row. All sites were characterised using previous season NDVI or yield maps.

Results

In replicated trials, soil salinity was significantly higher in the off-row sowing position which hinders crop uptake and the utilisation of applied P in P deficient soils. The increase in salt around the seed causes emergence and early vigour effects which translates to reduced grain yields.

Over two seasons of replicated trials at the Anna Binna site, there was a combined yield increase in barley and lentil of 1.42t/ha in the on-row position at the optimum phosphorus rate of 20kg/ha compared to no phosphorus.

Trends were similar over two seasons at the higher salinity Thiepvale site, with strong yield responses to phosphorus in the barley phase in the on-row position. Lentils recorded no yield gain from applied phosphorus in either sowing position.

Lentils are more sensitive to induced salt from applying fertiliser with the seed, with both sites recording reduced germination and biomass when moderate to high fertiliser rates were applied with the seed.

At both sites significant yield improvements at the optimal phosphorous rate translated into an increase in partial gross margin of over $800/ha in the on-row position compared to off-row over the two seasons.

Soil surveys demonstrated in the on-row sowing position nitrate N was lower, Colwell P was higher, and salinity was lower. A significant increase in soil moisture in the on-row position compared to inter-row was not recorded consistently across all 50 paddocks.

Results from demonstration sites were similar to replicated trials and paddock surveys. Moisture was higher in the on-row position, particularly at the surface (0-5cm). Nitrate N was higher in the inter-row and concentrated at the surface. Soil salinity was concentrated at the surface but decreased in the on-row position. Low production zones were linked to higher soil salinity and lower available phosphorus.