CAN YOU BUILD SOIL CARBON IN A DROUGHT? - ASM MID-TERM UPDATE

December 17, 2019

The answer to this question lies in the soils and what you have been doing to them over the years. Despite the “doom & gloom” there are many great stories out there showing how farmers have adapted to unreliable rainfall and manage to keep producing more with very little other than innovation and smart thinking.

 

In 2019, ASM started five internationally significant farm trials in the Wagga/Junee area and in Forbes NSW. The aim of the project is about measuring the benefits and costs of improving soil quality on the five farms. This includes the completion of a value proposition informed by benefit-cost analysis for compost-based soil improvement. The trials will continue up to December 2020 with additional applications of compost and amendments.

 

Despite the drought there has been already been some phenomenal changes and successes in the soils. Soil carbon is a key indicator of soil quality and results after as little as seven months of treatment show increases from very little right up to almost 1.0% in soil organic carbon. Here is an update of each farm trial at the halfway point of the project.

 

Site 1 Gregadoo Park Crop Production – Andrew & Karly Dumaresq

 

Compost was applied in Autumn 2019 and was sown to canola with conventional fertilizer treatment versus a range of compost treatments with and without fertilizer. Standard practices include no till, stubble retention, MAP at sowing, urea applied as needed through the season and lime/gypsum to lift pH and add sulphur.

 

The trials are located within a paddock that has a variation in soil type from a dermosol on flats at the northern end to a more fertile chromosol on slopes at the southern end. The same treatments were applied to both soil types. Soil samples were taken in September 2019 from each soil type comparing standard fertilizer treatments to compost only replacing all fertilizers.

 

On the less fertile northern flats, compost has maintained nitrogen levels with an increase of 32% in the nitrate form. There is an increase in pH from 6.84 to 7.31 and a 17% increase in nutrient availability (ECEC) and a 47% increase in conductivity. Phosphorous has increased by an average of 59% and sulphur by 90%. Magnesium has increased by 31% and potassium by 33%. Potassium is too high but will be corrected when the farmer continues with the application of lime to increase calcium to ideal levels.

 

A different set of responses to compost was seen on the more fertile southern slopes.  Different responses to the same compost from different soils is a common observation in the ASM R&D program. In this case, compost has maintained nitrogen levels with a 67% increase in the preferable ammonium form. Phosphorous has dropped by an average 32% with sulphur increasing by 43%. Potassium is too high but will be corrected when the farmer continues with the application of lime to increase calcium to ideal levels.

 

Note that soil organic matter and organic carbon have not made significant increases as yet on either of the soil types. There has been a slow increase over past years due to improved management practices. Levels are quite good for conventional farming but further increases are needed to optimize soil fertility and crop performance.

 

Satellite imagery (September 2019) has indicated that canola with the addition of compost (but no fertilizer) is falling behind in production. This treatment looks good in isolation showing that it is possible to produce broad-acre crops without chemical fertilizers. It is a matter of degree with fertilizer providing a slight production advantage. The farmer and his advisor have suggested the differences are due to a lack of nitrogen in the compost-only treatment. However, soil test results (see above) show no deficiency in nitrogen or other nutrients. It remains to be seen if these differences will translate into different yield results after harvest in December.

 

Site 1. Gregadoo Park. No visible difference between fertilizer and compost only treatments – all photos taken in September 2019

This project is funded by the NSW Government Waste Less Recycle More Initiative

 

 

Site 2 Gregadoo Park Pasture Production (phalaris, lucerne, sub clover)

 

This site was sown to a permanent pasture mix of phalaris, lucerne, and sub clover using conventional fertilizer treatment with and without compost. Standard practices include no tillage, controlled grazing, MAP at sowing, and no urea. Lime and gypsum have been applied to lift pH and add sulphur, respectively.This paddock has been sown into a 3-5 year pasture phase to feed livestock but mainly to increase soil fertility for a new cropping program. As a general rule, a managed pasture phase will increase soil fertility while a cropping program reduces soil fertility over time.

 

In the first year of treatment (2019), compost is already making valuable increases in soil fertility. Total nitrogen has increased slightly with a 62% increase in the nitrate form. There is an increase in pH from 6.12 to 6.49 and a 21% increase in nutrient availability (ECEC). Phosphorous has increased by an average of 59% and sulphur by 90%. Magnesium has increased by 31% and potassium by 33%. Soil organic matter has increased slightly.

 

The 2019 season is going well with prolific pasture growth observed soon after compost application with benefits continuing into October. These observations are supported by soil test results in September 2019 (see above). There is very high biomass with good growth and soil moisture across the whole paddock. The paddock is understocked with fat lambs to prevent pasture damage from over-grazing. The perennial pasture grass phalaris is dominant with sub clover also doing very well. Lucerne has established well but has sustained some frost damage. The differences in biomass between treatments is less obvious as the season progresses, however, pasture health remains superior with compost.

 

Site 2. Gregadoo Park. Excellent mixed pasture response from compost.

This project is funded by the NSW Government Waste Less Recycle More Initiative

 

 

 

Site 3 Tracton North Park Crop Production – Ryan & Claire Dennis

 

This paddock is a recent purchase by Ryan and indications are that it has been left with little management of unimproved pasture by the previous owner for many years. It has been sown to canola. Standard practices include no tillage, stubble retention, MAP at sowing, urea applied as needed through the season and lime or gypsum to lift pH and add sulphur.

 

In the first year of treatment (2019), compost is already making valuable increases in soil fertility. The farmer has included an additional treatment with guano side-by-side with the compost treatment. This has been beneficial in soil test results but to an overall lesser degree than compost. The soil analysis below is restricted to the compost trial site.

 

Compost application has increased soil organic matter by 18% with further increases needed. Total nitrogen has increased 33% with a 3-fold increase in the nitrate form and a 30% in the ammonium form. There is an increase in pH from 6.79 to 6.96 and a 32% increase in nutrient availability (ECEC) and a 3-fold increase in conductivity to an ideal level. Phosphorous has increased by an average of 3-fold and sulphur by 7-fold. Calcium has increased by 25% but is still too low. Magnesium has increased by 74% and potassium by 84%. Potassium is now too high but will be corrected when Ryan continues with the application of lime to increase calcium to ideal levels. Iron has fallen from toxic to acceptable levels.

 

The organic amendments compost and guano were surface applied as separate treatments then ploughed in to a depth of about 15cm. Cultivation was included in this case to remove the fungal pathogen rhizoctonia. Some minor soil loss occurred after a summer storm before sowing. This is always a risk with cultivation. Standard practice for Ryan is no-till with stubble retention. There were no obvious differences across treatments in September despite major improvements in soil test results for the compost treatment (see above). It remains to be seen if these differences translate into yield differences after harvest in December.

 

Site 3. Tracton North. No visible difference between fertilizer and compost treatments

This project is funded by the NSW Government Waste Less Recycle More Initiative

 

 

 

Site 4 Heaven Crop Production – Jason & Carolyn Willis

 

Jason & Carolyn are making the transition from conventional to organic cropping systems. Jason has experimented with and evaluated a range of biological treatments and amendments. At this point he is impressed with results from better management practices combined with organic amendments such as guano and seaweed extracts. The recent addition of compost to his program has delivered outstanding results superior to other amendments.

 

ASM experience over many years in our on-farm R&D Program has repeatedly demonstrated that soils with a history of good management on organic farms often respond rapidly and dramatically to the addition of good quality compost. This is also the case for this site.

Standard treatments include fish emulsions and guano. The addition of compost to a barley crop this year has increased soil organic matter and organic carbon by around 40%. Total nitrogen levels have increased by 53% with an increase of 66% in the nitrate form and 4-fold in the ammonium form. There is a 10-fold increase in pH from 5.93 to 7.08 and a 58% increase in nutrient availability (ECEC) and a 12% increase in conductivity. Phosphorous has increased by an average of 3 to 4-fold and sulphur by 3-fold. Calcium has increased by 43% to an ideal level for plant nutrition, which we find very unusual in southern NSW. Magnesium has increased by 76% and potassium by 47%. Magnesium and potassium are now too high but will be corrected when the farmer continues with the application of lime to increase calcium to ideal levels from a base saturation perspective. The only downside is a strong increase in sodium to mildly sodic levels. Once again, the addition of more lime will help to address this situation.

 

The increase in soil organic carbon, in seven months, is unprecended as far as we can find from published research and may represent a world first. This 10 hectare trial site has ‘drawn down’ around 1,500 tonnes of carbon dioxide equivalents from the atmosphere and only used 50 tonnes of compost. Soil carbon in the form of Australian Carbon Credit Units (ACCUs) is a financial product (recognised nationally and internationally) and the value of this carbon increase is approximately $18,000. It would also represent a 600% return on investment.

 

The compost treatment has delivered dramatic results with barley on this property. There was a rapid and strong visual response from the crop and topsoil as early as July with obvious differences between treatments. The crop has continued to perform well with small and timely rainfall events through the season. More recently, moisture stress is beginning to have an influence into spring with visual differences in crop performance less obvious between treatments. Productivity results will be known in December.

 

Site 4. Heaven. Guano (LHS) vs Compost (RHS). Greater crop vigour with compost.

This project is funded by the NSW Government Waste Less Recycle More Initiative

 

 

Site 5 Kara Kara Crop Production – Scott Mattiske

 

This site near Forbes has been sown to wheat using conventional fertilizer treatment with and without compost. An additional variable is compost surface-spread versus incorporated into the soil down to 15cm. Standard practices include no tillage, stubble retention, MAP at sowing, urea applied as needed through the season and lime or gypsum to lift pH and add sulphur.

 

Unfortunately, this part of NSW around Forbes is experiencing severe drought conditions. Scott took a calculated risk in sowing wheat in Autumn when sufficient soil moisture was still available. There was enough moisture for seed germination and seedling emergence but follow-up rainfall has been minimal. The treatment with compost cultivated into the soil had poor seedling emergence compared to compost spread on the surface. This may be due to moisture loss with soil disturbance but the crop has recovered and caught up apart from some dead patches. Despite harsh conditions the crop is still going but some surrounding farms have already cut and bailed for fodder to feed lambs born around now to avoid buying in feed.

 

 

Summing up

 

Drought is always a risk for field projects in broad-acre agriculture in Australia. Fortunately, sufficient rainfall in 2018-2019 has been received to sustain the season for the four project sites in the Riverina region. The Kara Kara site further north at Forbes has been less fortunate. However, there was sufficient soil moisture to sow wheat for the winter season. This site would normally have access to irrigation water from the Lachlan river. Extreme drought conditions have prevented access this year. It remains to be seen if this crop survives to deliver a complete set of performance data for the 2019 season.

 

ASM has produced a new set of guidelines for farmers who want to build their soil quality and soil carbon stocks. If you would like a free copy, please send me an email at norman.marshall@australiansoil.com.au.

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