Gray clay subsoils are massive (that is, they have few cracks), clayey and yellow or yellow-gray in color. The largest areas of gray clays occur in the eastern half of the great southern district of Western Australia. Gray clays are found in low-sloping sections of the landscape, often on valley floors.
Symptoms and causes of poor soil conditions
Strategies to improve soil conditions
Improved Management of Grey Clays
Management practices to improve grey clays
Note soil inversion, soil and root exposure, and incomplete incorporation of the green manure crop. The application of gypsum and/or lime to gray clays is done to change the soil chemistry by reducing the amount of exchangeable sodium on the clay.
Management opportunities to improve soil conditions
Improvements achievable in cropping systems
Weed populations in the crop were reduced when no-till crop establishment was applied, due to the lack of soil disturbance between the sown rows of the crop (Figure 16). Yield increases of this magnitude will pay for most of the costs associated with adopting various combinations of improved practices. The soil loosening treatment caused large and dramatic changes in the top 25 cm depth of the gray clay.
The large reduction in the bulk density of the surface soil in the deepened seedbed, compared to the bulk density of other soil management practices, is shown in Figure 14. The challenge of the deepened seedbed form of soil treatment is that crops on such seedbeds must actually. 2001: Very little precipitation fell in the first half of the season and above average rain fell in the second half (10% less rain than the long-term growing season median) 2002: The season was very dry in the first half and sparsely dry in the second half (20% less rain than the long-term median for the growing season).
The contrast of mid-season growth of wheat on normal (left) and deepened (right) seedbeds in September 2003. On the other hand, the percentage of exchangeable sodium, which is an indicator of the stability of the soil structure, decreased to values less than 4.0, significantly less than the value of 6.0 used to identify dispersive behavior in soils.
Improvements achievable in grazing systems
Alfalfa, being a summer-grown perennial legume, has the potential to: .. a) extract more water from the root zone soil than annual crops and pastures and thus provide a buffer against the onset of winter waterlogging and possibly groundwater recharge; and .. b) increase soil nitrogen and increase yields of subsequent crops. Additional water stored in the 0 to 100 cm profile depth relative to that stored in the profile under a lucerne pasture on a gray clay soil in Mindarabin. The relatively greater amount of water stored in late summer in rye cropping and grazing systems means that the drier soil profile under a ryegrass pasture will experience winter waterlogging, if at all, a month or two later than rye crops and pastures.
However, because profile water storage under Lucerne at the end of the growing season is smaller than that under winter crops and pastures, Lucerne pastures require significant summer rains to provide reasonable amounts of fodder throughout the summer. Importantly, the information in Figure 26 also shows that the drier soil profile below Lucerne (which acts as a buffer against winter flooding) is completely filled again after only one year after returning to a cultivation phase. Studies of the ability of alfalfa pastures to replenish soil nitrogen and increase yields of successive cereal crops over a year or two indicate that expectations for achieving a yield increase should be realistic.
These studies show that it is very dependent on the rainfall of the growing season in the first two seasons after the lucerne grazing to get an increase in the yield. If rainfall in the first one or two years of a growing phase after alfalfa is above average, grain yield increases of around 20% can occur.
Farming Practices for Improving Grey Clays
Cropping systems
The objectives of retaining stumps on gray clay soils are clear.. to protect the soil surface from raindrop impact to minimize spreading, sealing and crusting of the surface soil; .. to maintain and increase the level of organic matter in the soil; .. to facilitate deeper penetration of rain and conservation of soil moisture; and .. to control wind and water erosion. Another practice that helps overcome the challenge of clearing stubble during seeding is to use wide row spacings and sow in the interrows of the previous crop. Stubble retention should be practiced on gray clay soils due to the need to build organic matter, protect surface soil from raindrop impact, and improve deep infiltration and soil water retention.
Apply gypsum at a rate that stabilizes the structure of the soil surface to a depth of 8 cm to 10 cm. Organic carbon represents about 70% of the weight of organic matter in soil, which means that an organic carbon content of 1.4% represents about 2.0%. Inversion tillage will cause about 0.3% of the total organic carbon to decompose, representing about 21% (or 6.3 t/ha) of the soil's current organic matter.
The looseness of the seedbed is not maintained if it is subjected to compaction by traffic. Note the ability of the renovation tools to leave plants effectively undisturbed while thoroughly loosening the soil. Most, if not all, of the runoff will be generated by the unseeded roadway area.
Once the tracks are wet in winter, perhaps 50% to 80% of the rain that falls on the tracks will run off.
Grazing systems
There is very clear data showing that a perennial ryegrass-based pasture is much more productive than a perennial summer-growing alfalfa pasture. However, there is clear data that also shows that an alfalfa pasture (Figure 36) provides high quality forage in the summer-autumn forage gap period and that this pasture dries the profile more than any other herbaceous pasture. Such a combination of pasture types naturally also offers the farmer the opportunity to graze the alfalfa pasture during winter and spring and thus help to keep the ryegrass pasture in good condition.
There are two ways in which pasture and crops can be combined - a 'one year in, one year out' 1:1 crop:graze, or phased management, where cultivation and grazing are practiced alternately. On the other hand, phase farming represents the best of both worlds for gray clay management in mixed farming operations. It gives the farmer the opportunity to use all the better forms of soil management and crop rotation and to use both winter and summer growing perennial pastures.
There is no data or a substantial body of farmer experience on which to base advice on what the optimal phase duration is. 3 The pasture phase should include perennial pastures separated by winter and summer growth to capture the benefit of a quality stock feed supply for the summer-autumn feed gap and to avoid soil degradation of overgrazed and bare pastures during this period.
No-tillage seeding
Machinery Requirements for Improving Grey Clays
Stubble management
Gypsum and lime application
The latter alternative in a no-till regime is limited to the sown rows and is therefore quite incomplete. Research efforts are underway to inject gypsum and lime into the soil in a no-till regime to increase efficiency and reduce costs, but this falls far short of commercial reality.
Green manure incorporation
Deep cultivation and renovation
The former alternative leads to considerable breakdown of soil organic matter, which in the case of gypsum applications for structural improvement somewhat defeats the purpose. The undulating coulters, split shanks and steeply raked, flat cover crops that serve as bladed ploughs. The shanks and mulch sweeps are assembled to cut through the full width of the seed bed between each tractor traffic line.
Note that the entire bed is loosened and the disc harrows hanging from the back of the beam break up the crust without turning the soil over.
Controlled traffic Tractors
Note that here the measuring wheels of the bar have rows that are seeded immediately inside their track, so that the next seeded row (26 cm spacing) on the return trip causes the tire track to be obscured by seeded crop. If the crop area is not large, the air seeder can be mounted on the tractor. However, confirmation of the possible extension of their track width to 4 m, (ie to multiples of 2 m) must be obtained from the manufacturers (Figure 48).
Less expensive trailed tank sprayers can be easily adapted to a 6-foot or 6-foot track width by extending the axle on the sprayer tank to match the track width (Figure 49). Fertilizer spreaders are easily made in the farm workshop and mounted on the back of the tractor (Figure 50). Swaths can be aligned to fall between the harvester tracks to facilitate picking up the crop during harvesting (Figure 51).
Dump truck tires of 0.45 m wide with dump truck rims of the same size can be made to fit 3.66 m track width by welding the mounting disc into the rim at the correct position. Plus, the industrial grade rubber in these tires means they never need to be repaired or replaced.
Basis for comparisons
Comparisons of management options Cropping systems
Economics of Improved Practices for Grey Clays
A gross margin analysis similar to that for cropping practices was not possible for the limited data collected on grazing production. However, the complementary grazing productivity of winter-growing perennial grassland and a summer-growing Lucerne meadow has been used to illustrate their impact in terms of eliminating the need for supplemental late-summer-fall feeding. Assuming both types of pasture were adopted, the need for supplementary feed would almost completely disappear.
If this were the case, the average grazing gross margin for wool-producing sheep would increase from . This very conservative estimate represents a minimum annual average increase of 9% in gross margin profit for such a grazing company.
Five-year Average Gross Margins
