Implementation of irrigation practices for profitable resource efficient sugarcane production in the Ord : Final report CSE007

Abstract

Sugarcane is currently the major crop in the Ord River Irrigation Area (ORIA) in terms of area, occupying approximately 4000 hectares or a third of the irrigable area. It is also possible that further expansion could occur soon within the Ord Stage 2 area. The new industry is continuing to develop guidelines for and to initiate implementation of best management practice, to ensure the development of a profitable and sustainable industry. This project contributed to the provision of an extension service which is critical in assisting the industry in this development. Irrigation water application in excess of 30 ML ha-1 yr-1 was common commercial practice when sugarcane production commenced in 1995. High irrigation application not only impacted on profitability but also contributed to rising water tables and land degradation. Consequently this project aimed to build capacity in the community to save water and labour and to reduce rising water tables.

The APSIM-Sugarcane model (Keating et al., 1999) enabled the initial testing of scientific hypotheses of sugarcane production in the Ord. During the previous SRDC project (CSR022) certain adjustments were required for APSIM simulations under Ord conditions but these were not entirely satisfactory. In CSE007 it was necessary to introduce growers to a framework based on the Penman-Monteith (PM) equation. This framework is concerned mainly with daily crop evapotranspiration (ETC) for which it is more suited than APSIM-Sugarcane but does not consider much detail on crop physiology or soil physics. A number of experiments were conducted to improve both the APSIM and PM frameworks for a better working knowledge of the soil-plant-atmosphere continuum in the Ord.

From the APSIM based scheduling experiments we concluded that a 50% soil water deficit represented the lower limit of readily available water (RAW). It was then possible to derive RAW values (56 to 68 mm) for the major soil types in the Ord in the interests of balancing requirements for high sugar yields and reduced water use. Lodging rules introduced to APSIM for conditions in the east were able to explain a ‘slow-down’ phenomenon noted repeatedly in earlier experiments after about 30 t ha-1 biomass had been produced. More recently an early ratoon crop accumulated biomass rapidly up to 55 t ha-1 before slowing down. While the slow down was triggered by a combination of crop mass, soil water content and storm rainfall the physiology of the slow growth process remains unresolved.

The project made extensive use of a Bowen ratio energy balance (BREB) system which measures energy being used to evaporate water from the crop and soil (ETC). Daily water use in the Ord seldom exceeded 8 mm d-1 compared to original estimates from APSIM of more than 12 mm d-1. Annual net irrigation requirement based on the PM framework was 670 to 1628 mm and these estimates have been used to assess water requirements for sugarcane production in Ord stage 2.

The recent establishment of irrigated sugarcane in the Ord offered a chance to try new concepts of participatory action research (PAR). The end result of the PAR process was ‘WaterBalance’, a computer program which growers adopted readily as a scheduling tool as a result of their involvement in its development. In January 2006, three Ord growers were actively using the prototype WaterBalance to schedule their irrigations. These growers had a total of 22 blocks on the system. A fourth grower obtained weekly updates on the current scheduling interval via fax or email. WaterBalance was later superseded by WaterSense which combined WaterBalance with an earlier web-based irrigation tool for growers using limited water in the Bundaberg/Isis region. One Ord grower continues to use WaterBalance while the others have switched to WaterSense which has now been endorsed by the BSES Limited and the Cooperative Research Centre for Irrigation Futures. In all regions adoption by those growers familiar with the background research has been immediate. Indications are that the combined use of the Internet, PAR and concurrent research and demonstration will open the way for the adoption of research findings in the management of irrigation and possibly other aspects of sugarcane farming.

Evaluation surveys were conducted in 2003, 2004 and 2006 to assess perceptions and practices about irrigation and how these were influenced by the project. The 2004 and 2006 surveys in particular indicated how much irrigation practices had changed since the initial benchmarking survey was conducted by Wood et al (1998). This original survey reported an average water application per crop of 40 ML ha-1 and by 2006 growers reported an average use of nearly half this amount.