Abstract

Keywords

Introduction

Vertosols (cracking clay soils) are the predominant cropping soils in north-eastern Australia, and are typically uniform to at least 1 m depth (Webb et al. 1997). These soils can hold up to 250 mm/m of water, however, the presence of high levels of salinity, sodicity, acidity and high concentrations of chloride and sodium in the subsoils reduces soil water extraction and crop yield on many areas of the northern grains region (Dubbo NSW through to Emerald Qld) (Dang et. al. 2008). Subsoil constraints are estimated to cost growers around $80/ha over 1,400,000 ha in foregone income, which equates to at least $112 million per annum in the northern grains region (SIP08 2007). Poor water use by crops resulting from subsoil constraints also potentially contribute to environmental damage due to the mobilisation of salts from increased runoff and deep drainage.

The Grains Research and Development Corporation (GRDC) identified subsoil constraints as an important limitation to crop production in the northern grains region of Australia. Under strategic investment the five year Combating Subsoil Constraint Project (SIP08) commenced in 2002 targeting subsoils that constrain grain yield in the cracking clay cropping lands from Dubbo in NSW to Emerald in Qld. To help determine the impact of the project, surveys at commencement and completion of the project were undertaken to gauge growers’ and advisors’ knowledge, attitudes, skills, aspirations and practices (KASAP) relating to subsoil constraints. The surveys also identified the deficiencies and opportunities to achieve the KASAP targets and allowed growers’ and advisors’ input into what aspects of subsoil constraint research, development and extension needs most attention to the future subsoil constraint project.

Methods

In 2003, a 12 question survey was developed and completed by both growers and advisors (private and government) in the northern grains region. The survey collected KASAP information related to subsoil constraints that occur in the districts of the respondents. Surveys were collected at industry trade shows (AgShow; AgQuip), farmer meetings, workshops, field days, action-learning workshops and over the telephone.

During the last six months of the project (2007) a final project survey was conducted in the same geographic location. Respondents were asked to answer similar questions as in 2003, with the intention of comparing the 2007 results to that of the 2003 survey to determine the impact of the project. In 2007, stakeholders were first sent a copy of the survey in the mail, however due to a very poor response rate a professional survey company was engaged to contact stakeholders over the telephone.

To ascertain whether the responses in 2007 had changed from those in 2003, differences in responses between groups (farmers and advisors) were determined using a chi-square test.

Results

Stakeholder involvement

A total of 421 growers and 93 advisors responded to the 2003 survey and 392 growers and 49 advisors responded to the 2007 survey. Compared to growers, a greater proportion (P<0.001) of advisors have 'participated in workshops and/or field days' and fewer had 'never heard of the project' (Table 1).

Table 1. Level (%) of involvement in the project by stakeholders (2007 responses)

Involvement	Total	Growers	Advisors
Never heard of the project	32	36	6
Have heard, but never participated	37	38	29
Participated in workshops and/or field days	23	19	55
Actively involved	6	6	6
Other	2	1	4
Number of respondents (n)	435	386	49

Awareness of subsoil constraints

In 2003, a greater proportion (P<0.001) of advisors than growers responded that subsoil constraint were 'somewhat of a problem' with fewer responding 'small problem' and 'not a problem' (Table 2). The 2007 survey results showed a greater proportion (P<0.001) of advisors responded 'somewhat of a problem' compared with growers (Table 2). This is the same as the 2003 response, indicating that most advisors still believe subsoil constraints affect between 10-50% of land in their districts. Although there was no significant difference in the responses between the two survey periods (2003 and 2007), it is worth noting the proportion of advisor respondents indicating ‘not sure’ decreased from 15% to 0% during this time (Table 2).

Table 2. Awareness (%) of subsoil constraints in 2003 versus 2007

	2003		2007
Problem level	Growers	Advisors	Growers	Advisors
Not a problem	7	0	15	0
Small Problem (0-10% of land affected)	26	8	31	11
Somewhat of a problem (10 – 50% of land affected)	32	62	28	79
Major problem (50 – 100% of land affected)	20	15	13	11
Not sure	15	15	14	0
Number of respondents (n)	421	93	385	47

Overall knowledge of subsoil constraint

The end of project survey asked stakeholders to rate how their knowledge of subsoil constraints had changed over the last five years. Compared to advisors, a greater proportion (P<0.05) of growers had indicated that their knowledge had not improved in all areas (Table 3). A greater proportion of advisors indicated that their knowledge of the cause of various subsoil constraints' had improved moderately, and knowledge of 'the impact of subsoil constraints on crop performance’ had improved a lot (Table 3).

Table 3. Responses (%) to four areas of subsoil constraint knowledge

Areas:	Hasn’t		Slightly		Moderately		A lot
	Growers	Advisors	Growers	Advisors	Growers	Advisors	Growers	Advisors
The cause of SSC	13	2	39	29	28	48	19	21
Which SSC are present	20	2	33	33	26	39	21	26
SSC impact on crop performance	17	0	30	26	35	36	18	34
Ways of managing soils with SSC	17	2	36	36	30	43	18	19

Knowledge of the impacts of subsoil constraints

In 2003, a high proportion of both respondent groups agreed that subsoil constraints ‘limit plant rooting depth’ and ‘reduce plant available water (PAW)’, and this level of agreement was maintained in 2007 (Table 4). However more growers in 2007 were unsure whether subsoil constraints ‘limit rooting depth’, ‘reduce PAW’, and ‘can be successfully managed’ compared to advisors (Table 4). More growers agree that subsoil constraints ‘reduce sustainability’, whereas more advisors are unsure if subsoil constraints ‘reduce sustainability’ (Table 4).

Comparing 2007 results to 2003, a lower proportion of growers in 2007 were unsure if subsoil constraints ‘limit plant rooting depth’, whereas a lower proportion of both groups were unsure if subsoil constraints ‘increase disease risk’ and ‘make management more difficult’ (Table 4). These results indicate a change in knowledge by both groups, as fewer growers and advisors are unsure about the impacts of subsoil constraints.

Table 4. Responses (%) on the impact of subsoil constraints

Subsoil Constraints	Agree				Disagree				Unsure
	Growers		Advisors		Growers		Advisors		Growers		Advisors
	2003	2007	2003	2007	2003	2007	2003	2007	2003	2007	2003	2007
Limit plant rooting depth	82	84	98	98	2	4	0	0	16	12	2	2
Reduce Plant Available Water	80	83	98	94	3	3	0	4	17	13	2	2
Can be successfully managed	52	66	52	67	3	3	1	6	46	31	47	27
Reduce crop yield	83	91	92	96	2	2	4	0	15	7	3	4
Reduce profitability	85	90	86	83	3	1	5	2	12	8	9	15
Reduce sustainability	53	72	67	45	9	10	14	26	39	18	18	30
Increase disease risk	34	42	33	38	12	19	12	21	54	40	55	42
Make management more difficult	74	82	87	89	6	9	2	4	20	9	11	6

Managing subsoil constraints

In 2003, a significantly higher proportion (P<0.001) of advisor respondents (68%) compared to grower respondents (39%) indicated that they manage soils with subsoil constraints differently to those without (Table 5). In 2007 these responses have significantly increased, with 68% of grower and 90% of advisor respondents indicating that they manage soils with subsoil constraints differently to those without (Table 5). In comparison to the growers surveyed, the proportion of advisors in 2007 who had clients that were managing soils with subsoil constraints differently to those without was significantly higher (P<0.001) Table 5).

Table 5. Responses (%) to manage soils differently with subsoil constraints

Response	Growers		Advisors
	2003	2007	2003	2007
Yes	39	68	68	90
No	49	13	12	0
Don’t have SSC	12	19	1	2
Don’t advise on SSC	na	0	19	8
Number of respondents (n)	421	385	93	49

Of the growers who were managing soils with subsoil constraints differently, a range of techniques were used including: selecting tolerant crops/varieties, zero/minimum tillage, different fertiliser programs, deep ripping and replacing cropping with pastures. The range of techniques being advocated by advisors included: crop and variety selection, crop rotations, adjusting yield predictions and inputs (fertiliser, seeding rate) based on severity of subsoil constraints, quantifying zones where differences occur and managing inputs within them, adjusting enterprise selection (cropping vs pasture vs trees) depending on subsoil constraints severity and crop profitability, and ameliorating sodicity problems with gypsum.

Discussion

In comparison to growers, advisors were more aware; more actively involved in the project; and learnt more about the causes, impact and management of subsoil constraints. The impact gap between growers and advisors reflects the project strategy of directly targeting advisors through the action learning workshops, with the anticipation that information would then flow to a large number of growers. Advisors are also more likely than growers to independently seek information from researchers. Results indicated that information didn’t flow from the advisor to their client as anticipated, possibly because some growers simply employ a professional to advise them what to do, rather than fully explain the complexities of the soil chemistry of subsoil constraints. Overall, there was indication that both groups were more confident in their knowledge of subsoil constraints at the end of the project than at the commencement, and this is evidenced by the lower proportion of unsure responses in 2007.

The SIP08 project was the principal consortium undertaking subsoil constraint RD&E in the GRDC northern grains region. While subsoil constraint RD&E was concurrently conducted in other parts of Australia, information derived from this project resulted in significant changes to the number of growers and advisors who manage soils with subsoil constraints differently to the soils without. In 2003, 68% of advisor respondents and 39% of growers indicated that they manage soils with subsoil constraints differently, compared to 90% of advisors and 68% of growers in 2007. This willingness to participate in activities (and ultimately change practices) can be attributed to the high interest in soil related issues at the time. However, about 30% of both groups are unsure if subsoil constraints can be successfully managed in the long term. Both groups are better equipped to make more informed decisions about subsoil constraints, which will enable the ongoing economic performance improvement of districts with subsoil constraints.

Conclusion

At the commencement of the project, many growers and advisors were already aware of how much land is impacted by subsoil constraints and which constraints occurred in their districts. This level of awareness over the last five years is broadly unchanged. A large number of growers and advisors have participated in project activities; however there has been a larger impact on advisors compared to growers. Significant increases in knowledge of the impacts and management of subsoil constraints are apparent.

More growers now believe subsoil constraints can be profitably managed, and consider that they have the skills to cope with subsoil constraints. This is reflected in a significant increase in the number of growers and advisors indicating that they manage soils with subsoil constraints differently. The evaluation of stakeholders has assisted in the development and formation of the next subsoil constraints project in the northern grains region: Advanced Techniques for Managing Subsoil Constraints.

Acknowledgments

We thank the DPI&F Communication and Information team (Stephen Smith) and Business Information Unit (Susan Jones) for coordinating and undertaking mail and phone surveys. The contribution of Brenda Leighton who undertook data entry, and both David Reid and Christina Playford (DPI&F Rockhampton) who undertook the statistical analysis are acknowledged. Special thanks go to the growers and advisors who kindly responded to both surveys.

References

Dang YP, Dalal RC, Mayer DG, McDonald M, Routley R, Schwenke GD, Buck SR, Daniells IG, Singh DK, Manning W and Ferguson N (2007) High subsoil chloride reduces soil water extraction and crop yield from Vertosols. Australian Journal of Agricultural Research 59: 321-330.

SIP08 (2007). Combating subsoil constraints: Project results book. (Eds. Dang, Y, Buck S et. al.), pp. 72. (Queensland Department of Primary Industries & Fisheries).

Webb AA, Grundy MJ, Powell B, Littleboy M (1997) The Australian sub-tropical cereal belt: soils, climate and agriculture. In ‘Sustainable crop production in the sub-tropics’. (Eds AL Clarke, PB Wylie) pp. 8-26. (Queensland Department of Primary Industries, QI 97035).

• "Global Issues. Paddock Action." Edited by M. Unkovich. Proceedings of 14th Agronomy Conference 2008, 21-25 September 2008, Adelaide, South Australia.