Photo A: Infiltration into water repellent soil of a one per cent blue dye solution in water. taken about two hours after blue dye application on 22 September 2011 and (b) nine days later following 27 mm of rainfall, on 1 October 2011 in a wheat crop sown on 25 May 2011 at Wanilla, South Australia..

Photo A: Infiltration into water repellent soil of a one per cent blue dye solution in water. taken about two hours after blue dye application on 22 September 2011 and (b) nine days later following 27 mm of rainfall, on 1 October 2011 in a wheat crop sown on 25 May 2011 at Wanilla, South Australia..

Photo B: Blue dye solution entered the soil via root pathways in the surface repellent layer, but below this layer water spread horizontally, more evenly wetting the non-repellent sub-soil. Photos: CSIRO and SARDI: reproduced from Roper et al. 2021.

Photo B: Blue dye solution entered the soil via root pathways in the surface repellent layer, but below this layer water spread horizontally, more evenly wetting the non-repellent sub-soil. Photos: CSIRO and SARDI: reproduced from Roper et al. 2021.

Seeding next to the previous year’s crop row (near-row seeding), can increase grain yields on water-repellent soils.
That is the conclusion by a group of CSIRO scientists and State Government agricultural research officers, who held long-term field trials at four sites – near Moora, Pingrup and Calingiri in Western Australia and Wanilla in South Australia.
In earlier research, published by the CSIRO team in 2013, it was shown that the combination of no-till and stubble retention preserved old crop roots, which behaved as pathways for water infiltration into water-repellent soil, effectively by-passing repellent surface soil layers.
This led to the hypothesis that near-row sown crops would perform better than inter-row sown crops. Furthermore, some farmers experimenting with seeding position noticed yield advantages with near-row sown crops.
Hence, the field evaluation compared near-row sowing with inter-row sowing on water-repellent soils.
Near-row sowing (sometimes referred to as on-row sowing) is usually aligned within 2cm of the previous year’s crop row to avoid disturbing existing root pathways.
The key results showed significant increases in above-ground plant biomass accumulation (Moora) and grain yields (Moora and Wanilla) by near-row sowing compared with inter-row sowing, particularly under no-till and stubble retention.
But these differences were reduced after moderate or deep cultivation, which either buried repellent surface soils or disrupted root pathways.
At Calingiri and Pingrup, where near-row sowing had been practised for more than four years, and at Wanilla, soil water contents were higher in the crop row than the inter-row by up to four per cent, and this was associated with significantly reduced repellency (Calingiri and Pingrup) and larger communities of wax-degrading bacteria (Pingrup; the only site at which microbial communities were measured).
The paper’s conclusion was that near-row sowing may enhance crop production directly through improved water infiltration down old root pathways, and indirectly by reduced soil water repellency in crop/stubble rows.
The authors believe near-row sowing is potentially a low-cost management tool for enhanced crop production on water-repellent soils.
At the Moora site, where soils were severely repellent, near-row sown crops produced more crop biomass than inter-row sown crops throughout the growing season regardless of tillage practices which included no-tillage, moderate tillage (off-set disc) and deep tillage (spader).
This translated to significantly higher grain yields in near-sown crops than inter-row sown crops, except for the spaded treatment which yielded the same for both near-row and inter-row sown crops.
There were no differences among near-row sown treatments regardless of previous one-off tillage treatment. Near-row sowing under no-till yielded similarly to those sown near-row following tillage (off-set disc or spader) without the additional cost of the tillage treatments or the associated risks of erosion and loss of soil organic matter.
However, soils with extreme soil water repellency may require intense amelioration management, in the form of strategic (one-off) deep tillage or clay application to increase in-row plant and root system densities capable of channeling enough water down the soil profile to benefit near-row sown crops in the following season.
Furthermore, strategic deep tillage can overcome multiple soil constraints such as compaction and subsoil acidity through lime incorporation and improve subsoil fertility, in addition to overcoming topsoil water repellency.
Deep tillage should only be used as a one-off treatment to ameliorate significant soil constraints.
Repeated intense cultivation can significantly reduce soil organic matter by disrupting stable organic matter networks and promoting its decomposition by soil microorganisms.
Organic matter is important for crop productivity because it increases water holding capacity in soil and provides nutrients for soil microorganisms and for plant growth.
This was demonstrated previously by the CSIRO team in a 10-year field trial, on the South Coast of WA, which showed that low soil organic carbon and surface crop residue cover, caused by repeated cultivation and stubble burning, reduced soil water contents and grain yields.
Furthermore, rebuilding soil organic carbon and surface crop residue cover at the South Coast trial site, following the return to no-till and stubble retention, was extremely slow.
At the Wanilla site in South Australia, near-row sowing again produced significantly higher grain yields than inter-row sown crops. However, there was no effect of cultivation on yields at this site, probably because tillage intensity was very low compared with the Moora site.
Visual observations and soil measurements pointed to a hydrological explanation for the yield benefits seen under near-row sowing, and this was independent of the severity of repellency.
Similar to observations made by Roper et al. (2013), blue dye solutions, applied to the surface of soil at Wanilla, flowed down the soil profile through root channels, by-passing the surface repellent soil layer (Photo A) which was severely water repellent.
Once the solution reached the more wettable subsoil below, water moved horizontally, wetting up this layer more uniformly (Photo B).
These root pathways have been shown to persist well into the following season (Roper et al. 2013) and hence, have the potential to improve water availability to new crops sown in their vicinity.
Measurements of soil water contents in the crop rows compared with crop inter-rows supported this visual evidence.
Observations at Pingrup, indicated that soil water contents were consistently higher in crop rows than the inter-row (by up to 4%) and that this was associated with a progressive decline in the severity of repellency and an increase in the numbers of wax-degrading bacteria.
This implied that reductions in soil water repellency in the crop or stubble row were due, at least in part, to microbial decomposition of waxes responsible for water repellency.
These findings are supported by Gupta et al. (2018) who showed that microbial biomass and microbial diversity were significantly greater in the crop and stubble rows than in the inter-rows in sandy soils at two locations in South Australia.
The results of field trials reported in the near-row sowing paper support anecdotal evidence that the benefits for crop productivity on water repellent soils under the combination of no-till and stubble retention can be enhanced by seeding close to the previous season’s crop rows (near-row sowing) to take advantage of water infiltration down old root pathways which both promotes plant growth and stimulates populations of wax-degrading bacteria.
The paper’s authors were:
Margaret M. RoperA,* , Phil R. WardA, Giacomo BettiB,E, Stephen L. DaviesB , Nigel WilhelmC, Ramona KerrA, Shayne F. MicinA and Terry BlackerD
Author affiliations, A: CSIRO Agriculture and Food, Wembley, WA; B: Department of Primary Industries and Regional Development, Geraldton; C: South Australian Research and Development Institute, Urrbrae, SA; D: South Australian Research and Development Institute, Port Lincoln; E: CSIRO Agriculture and Food, Glen Osmond, SA.
The full publication can be accessed via the link:https://doi.org/10.1071/SR21142 and selecting the PDF button.

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Publish Date: 
Tuesday, June 28, 2022