Improving the sustainability of irrigated maize (Zea mays) on sodic soils in the Lachlan Valley of New South Wales

Abstract

In recent years, the expression “Sustainable Agriculture” has entered public discourse on social, economic, and ecological issues, especially in the context of analysing the negative effects of certain crop production practices. For example, efficient irrigation is now essential due to the ever-changing political environment in respect to water access. Furthermore, interest in alternative weed control methods has grown with an emphasis on reducing tillage and pesticide use.

To achieve a sustainable agro-industry, new systems for crop production must be found. One such system, for irrigated maize on sodic soils in the Lachlan Valley was hypothesized and tested in the research reported here. This system incorporated the use of drip irrigation on permanent beds, with the use of residue retention through zero tillage and the use of legume cover crops over winter. Growth, yield and water use efliciency of maize grown under different irrigation methods were measured in order to provide information towards the formulation of guidelines for best irrigation practice management. The new cropping system was compared to the standard practices of the Lachlan Valley such as flood irrigation and conventional tillage.

In an experiment conducted to compare four irrigation methods border check (B) irrigation used 6.3ML of irrigation water; drip (D) irrigation reduced this volume by 52% and furrow (F) and permanent bed (P) irrigation had intermediate water requirements. From 15 DAS, crop LAI and dry matter were lowest in B and highest in D compared with other irrigation methods. Despite the large difi‘erences in crop growth, grain yields were similar in all treatments except B, which was reduced by up to 15%. The water use efficiency of yield ranged from 1.80 (in border check) to 4.05 (in drip) t/Ml due to the large differences in the quantity of water applied to each treatment.

During the production of the legume cover crop over winter, dry matter yields were lower than expected from the literature. Poor growth may have been attributable to herbicide residues remaining in the soil from the maize crop. Experiments were conducted to test the tolerance of the clover species Trifolium subterraneum cv. Nungarin, Trifolium balansae cv. Paradana and Trifolium vesiculosum cv. Zulu to the herbicides atrazine and metolachlor, that are commonly used in maize production systems in the district. All three clover species showed low tolerances to the herbicides, with subterranean clover showing the highest tolerance. Substantial retardation of growth occurred in the subterranean clover with atrazine concentrations of less that 1% of the recommended rate (9 g ai/ha).

Sustainable production of irrigated maize on sodic soils in the Lachlan Valley of New South Wales will involve the adoption by farmers of Best Irrigation Management Practices (BIMP’s). Such practices identified in the literature or by experimentation in this thesis include the following: i) the application to soil of gypsum and lime; ii) the use of permanent beds for cropping, and preferably with drip irrigation; iii) the production of a winter cover crop; and, iv) the use of zero-tillage where practical.

Management of cropping systems will continue to be influenced strongly by economic factors, as growers try to remain viable. Soil erosion, continuous cropping and soil fertility, interactions between crops, and nitrogen cycling and management must be addressed. Farming practices which include reduced tillage, crop rotation, opportunity cropping, legumes and fertilizers can be better utilised by farmers to improve sustainability and subsequently profitability.