Sustaining soil resources on dairy farms based on crops in southern Queensland

Chataway, Robert G. (2004). Sustaining soil resources on dairy farms based on crops in southern Queensland PhD Thesis, School of Natural and Rural Systems Management, The University of Queensland.

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Author Chataway, Robert G.
Thesis Title Sustaining soil resources on dairy farms based on crops in southern Queensland
School, Centre or Institute School of Natural and Rural Systems Management
Institution The University of Queensland
Publication date 2004
Thesis type PhD Thesis
Supervisor Ken Rickert
Tom Cowan
Total pages 261
Collection year 2005
Language eng
Subjects L
300100 Soil and Water Sciences
300901 Farm Management, Rural Management and Agribusiness
Formatted abstract

The forage base on many dairy farms in southern Queensland relies on a succession of grazed cereal crops rather than pastures. Cropping based farms are most common where rainfall is less than 800 mm/annum, soils are clay based and irrigation is limited. A program of annual cropping based around cultivated fallow periods and minimal fertiliser inputs has been possible for many years due to the structural stability and inherent fertility of the regions dominant arable soils (Vertosols). However in the long-term these farming practices are not sustainable as they rundown soil fertility, expose the soil to water erosion and increase the chance of soil structural decline. There is a need for systems of farming that better sustain the soil resource base and are as or more productive. A six-year research and development project was conducted to evaluate a number of strategies used by the grains industry to maintain soil productivity. These strategies concerned tillage, cropping frequency, nitrogen (N) fertiliser use, annual legumes, ley pastures and the use of feedlot manure.  


A survey and a series of on-farm experiments, with varying levels of farmer participation, were the main research activities used to evaluate strategies. The methodology used in the research sought to embody principles of Farming Systems Research (FSR), with its emphasis on participation, multi-disciplinarity and holism.  


One hundred and twenty farmers representing 20% of all producers in the region completed a mail-out survey. The survey sought information on farmer's practices and attitudes to arable land management with specific questions on pasture use, cropping frequency, zero tillage and plant nutrition. The survey showed that dairy farmers were generally familiar with and understanding of the potential benefits of alternative approaches to farming. However, issues were raised that needed consideration in the transfer of practices developed for grain cropping to dairy forage production. These included concern that an increased emphasis on pastures would result in lower and less-reliable forage production; that double-cropping is practiced out of necessity rather than in the belief it is a better way to farm and that zero tillage may not be suitable on clay soils that have been trampled by cattle. Farmers also indicated their desire for a greater role for legumes in future farming systems.      


The field studies were conducted on a number of farms in the Darling Downs and South Burnett regions. At two sites located on contrasting soils, a well-structured Black Vertosol and a structurally impaired Sodosol, 15 different cropping and pasture systems were evaluated in two randomised, replicated experiments. Forage systems were evaluated for their productivity, water use efficiency (WUE), impact on soil fertility and their potential to protect the soil from erosion. These trials were conducted under raingrown, grazed conditions. Mean annual rainfall during the trial period was 595 (Vertosol site) and 667 mm (Sodosol site) relative to a long-term mean of 662 mm/annum. Following the establishment of these major experiments, additional investigations were undertaken by another eight groups of farmers and agency staff to evaluate specific technologies further in their regional area. These groups involved a higher level of farmer participation, focused only on one or two technologies and used a combination of field trials, discussion and expert questioning in their evaluation of technologies.  


The major field studies showed that the choice of cropping season (summer versus winter) was more important than particular agronomic interventions for sustaining the productive capacity of the soil resource base. Summer cropping systems, based on nitrogen fertilised grass forage crops had an overall WUE of 9.5 to 15 kg DM/ rainfall. Soil organic carbon (OC) levels generally rose under these systems and when combined with zero tillage the potential to provide high levels of surface cover over the fallow period was high. On the other hand winter dominant systems were more vulnerable to soil OC decline and erosion. They were also relatively inefficient users of water with less than 20% of the summer dominant rainfall being stored over the fallow period and an overall WUE of 4 to 7 kg DM/ rainfall.  


With respect to particular technologies, zero tillage was found to be able to be successfully incorporated into dairy forage systems. While it gave no production advantages over conventional tillage in fixed summer or winter cropping programs it preserved crop residue better and where cropping frequency was increased enabled crops to be established with improved timeliness.  


Current industry standard rates of nitrogen fertiliser (55 kg/ha.crop) were found not to be limiting summer or winter forage production on the Sodosol soil. However a higher rate   used in the summer cropping program on the Vertosol (175 kg /ha.crop) was generally beneficial, increasing the overall WUE from 9.5 to 15 kg DM/ rainfall. For the winter crop at this site, a yield response to additional N fertiliser applied (55 versus 105 kg/ha.crop) was recorded in only one of five years.  


Annual legumes grown in rotation with grass forage crops were found to offset fertiliser N requirements and increase overall forage quality. Summer legumes offered greater comparative advantages over tropical grasses than winter legumes over temperate grasses, however legumes were generally less effective than the grass forage crops in rebuilding soil OC. Where farmers wish to include more legumes in their cropping program, or have an emphasis on cool season forage production they may consider the application of feedlot manure as a strategy for improving soil OC. The studies found that feedlot manure (15-25 t/ha) gave rapid improvements in soil OC and N concentration.  


With respect to pastures, lucerne leys were relatively easy to establish, produced highquality forage, and provided substantial residual soil N benefits. In contrast, lucerne and grass mixes were harder to establish than lucerne on its own and they gave no production or soil restoration advantages. A third alternative, tropical grass swards fertilised with 200 kg Nlha.annum, were not easy to establish but showed greater potential to restore soil OC than the lucerne based leys. However, forage quality was low, growing costs high relative to lucerne and the improvement in soil OC was not greater than that achieved under a series of annual summer grass crops.  


The eight additional investigations undertaken by groups of farmers and agency staff focused on evaluating; the usefulness of feedlot manure as an adjunct to bagged fertiliser, the productivity of alternative ley pastures and the value of zero tillage as an alternative to conventional tillage in farming systems. With respect to feedlot manure, the investigative groups determined that where farms are located in close proximity to suppliers the manure was a cost effective ·mixed fertiliser' However, if soils are well structured, and a mixed fertiliser is not required, a targeted manufactured fertiliser will generally be preferred. The pasture studies provided a better appreciation of the strengths and weaknesses of various ley mixes. The studies reinforced findings from the major field evaluations and farmers' own experiences that it is difficult to routinely establish tropical grass and legume pasture leys in the South-west dairy region and that the temperate grass Bromus willdenowii is worthy of further investigation for use in short term leys. Investigations into zero tillage supported findings from the plot studies that zero tillage could be successfully incorporated into a grazing and cropping system. The issue of compaction of heavy clay soils by cattle was reviewed, and it was determined that if cattle could be kept off cropping soils when wet that this problem could be mitigated.  


In evaluating and developing strategies to better sustain the soil resource base on dairy farms, the project team moved, over time, toward a methodology that placed greater emphasis on participation, multidisciplinarity and holism - Farming Systems Research. The project went some way toward using a FSR approach; single technologies were combined in various ways to form different 'forage systems' for evaluation, farmer opinions were sought on attitudes to arable land management, and farmers participated in the development, critiquing and testing of systems through a series on-farm experiments. However, the project fell short of FSR ideals in a number of aspects and future studies with similar goals should ensure; a greater effort in multidisciplinarity in the initial description and identification of constraints of the farming system, a greater emphasis on farmer involvement in project development and the interpretation of field study findings, and less emphasis on on-farm experiments and more on developing ·conversations' with farmers to better understand the social and economic implications of proposed interventions.  


In conclusion, FSR offers potential benefits to the study of complex farming systems such as cropping based dairy farming in southern Queensland. There is a range of technologies suited to farming systems in this region that will enable productivity and sustainability to be achieved. Most importantly farming programs need to place a greater emphasis on summer over winter cropping.

Keyword Dairy farms -- Queensland, Southeastern
Soils -- Queensland, Southeastern
Vertisols -- Queensland, Southeastern

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