Cotton is a relatively new irrigated crop in Southern NSW and has proven to be financially profitable. The cotton growers in Southern NSW need to know more about their soils so that they are able to refine soil-related management practices. The growers are facing a number of soil-related challenges and need improved local soils information. The irrigated cotton soils of Southern NSW are quite different from the cotton soils in the northern cotton regions. In Southern NSW the soils are highly variable and also the region has a distinctively shorter growing season which causes other management problems. Parts of the region include rice cropping or have a history of growing rice and this has unique implications on the soil for growing cotton. This scoping study was commissioned by CRDC because there was a recognised lack of understanding on the cotton growing soils and the associated soil management practices in Southern NSW. It was recognised that there was a need to identify knowledge gaps, to establish research questions that relate to the cotton soils and their management in Southern NSW and to report on the current information available on cotton soils.

The approach taken in this study involved two main components as follows: (i) surveys and interviews with growers and consultants and (ii) a desktop study of data and literature for soils and soil management practices. Initially a research focus group was formed to formally receive expert opinion on the level of understanding of irrigated soils in Southern NSW and also to identify some research priorities. Written surveys were completed by the 13 growers and 5 consultants that were interviewed one-to-one. This ensured that the study thoroughly engaged with the local cotton industry. The interviews were semi-structured as they were guided by 9 primary questions. Each interview lasted between 40-60 minutes, was recorded and transcribed. Growers and consultants were selected to cover differences in terms of experience, cotton area, soil type and location. The desktop component of the study involved reviewing and evaluating soils/ soil management practice data and information from Southern NSW and other regions where cotton is grown.

The interview responses indicated that most growers were using high levels of nitrogen in their cotton systems which appeared to be based on a risk management approach. The use of manures and stubble was fairly widespread among those interviewed, however many growers were uncertain about the nutrients supplied from manures. Issues relating to the short growing season were acknowledged by growers; with soil temperature and establishment issues at the start of the season and soil compaction concerns at harvest. The pressure and challenges associated with back-to-back cotton were frequently mentioned, although this may relate to the current water availability and cotton prices. Regardless of the reason there were several soil issues associated with crop rotation such as stubble management, cultivation and compaction which were raised as problematic. On stubble there were issues around getting sufficient breakdown before the next crop and the tie-up of nitrogen. With cultivation the challenge was related to the time pressure for activities such as pupae busting, stubble incorporation and bed formation. Compaction was mentioned as a serious issue by growers/ consultants from all districts in Southern NSW. Several scenarios were identified as high risk for compaction and some respondents provided options to avoid compaction, but there was uncertainty regarding the extent of or impacts from compaction. Comments on irrigation primarily centred around setting start date, and the decisions around irrigation interval during the season. When irrigating most growers described as though there was system (or layout) ‘lock-in’ and once they started irrigating there was very little opportunity for flexibility. Some soil issues such as acidity and salinity do not seem to be widespread, but more spatially isolated to specific cotton soils in Southern NSW. As cotton is a relatively new crop for some growers it appeared as though some respondents were learning through experience. Growers mentioned several different sources of soils information with advice from consultants and information from other growers being very important.

A review of the current soil survey data for Southern NSW was undertaken. The two main on-line databases are: eSpade/ SALIS (NSW Office of Environment and Heritage) and ASRIS (CSIRO). Areal estimates of soil order in Southern NSW showed that Vertosols are the dominant soil in the Murrumbidgee valley and cover 43% of the Lachlan valley. These are very approximate estimates because they are based on very limited soils and landscape data.

Assessment of previous cotton soils research (mostly from Northern NSW) reveals that there are opportunities to utilise results and translate them to Southern NSW. We established that there are limitations to utilising research from elsewhere; however as a guide we identified some key regional factors such as mineralogy or soil pH which strongly influence major soil processes. Likewise the same approach was applied to soil management practices. Again a series of different regional factors was found which have a large influence on the effectiveness or difficulty associated with implementing soil management practices.

The evaluation of databases and literature on soils and soil management practices also identified gaps in understanding for the cotton soils in Southern NSW. Exploration of soil survey databases indicated there are large differences in the coverage and quality of soils spatial data across Southern NSW. Major soil degradation processes including acidity, erosion, salinity and sodicity were each selected with research areas described which relate directly to the soils in this region. Soil chemical properties were examined and in many cases there is no published data available. A lack of understanding on the impact of different management practices on soil physical and hydraulic properties was evident. Quantification of soil hydrology on cotton soils and soil water properties is required. Very little information is available on the soil biological condition of the cotton soils in the region. At the farm scale there is a lot of uncertainty on issues such as compaction, stubble, tillage and crop rotations.

From this scoping study recommendations are made for future research and development activities. We suggest that a soil management practice case study is undertaken to improve understanding on the how and why growers make decisions in four areas: sowing and crop establishment, nitrogen fertilizer applications, irrigation scheduling and with picking and cultivation. We recommend that work is commenced to improve the soil spatial data for the cotton soils of Southern NSW with the highest priority on determining the extent of sodicity. A soil nutrient database is recommended as a means to increase industry confidence on the levels of critical soil test values. Such a database could enable benchmarking and also contain established crop nutrient response curves. Attention on soil physical condition is advised because of the unique soils found in the region and the uncertainty with the impacts from soil management practices. Finally, all future cotton soils research and development undertaken in Southern NSW should aim to produce soil management guidelines to identify and encourage the adoption of best practices.