Aerobic Rice with or without Strategic Irrigation in the Subtropics

Sachesh Silwal,David J Midmore,Surya P Bhattarai

doi:10.3390/agronomy10111831

Sachesh Silwal, David J Midmore + Show 1 more

Open Access

https://doi.org/10.3390/agronomy10111831

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Abstract

Modern rice varieties adapted to aerobic (dryland) conditions have expanded to new rice growing systems thanks to their plasticity in adapting to rainfed and irrigated conditions. This is important because, as water becomes scarce in paddy rice regions (as it is already in Australia), there will be a move towards tropical to subtropical dryland rainfed rice with attendant problems of drought and low temperature. To assess rice adaptability in the wet season of the semi-arid subtropical conditions of coastal central Queensland, field experiments were established for a late season (in January) planting in 2014 and early season planting in November 2015 with 13 varieties developed by Australian Agriculture Technologies (AAT) Ltd were seeded in a vertisol soil. This was to assess their adaptation to rainfed conditions and their response to strategic irrigation. Water scarcity and low temperature prior to and at flowering were important factors constraining yield. Early flowering varieties in the late season planting escaped the otherwise cold and drought stress during the reproductive stage and had higher yields. In the second year, earlier planting made possible with strategic irrigation avoided the low temperature constraint on yield, but without follow-up strategic irrigation, yields were still low. The average yield of varieties increased from 1.5 times (AAT 4) to 16.3 times (AAT 15) with strategic irrigation compared with rainfed yields averaged across years. The increase in yield with strategic irrigation was associated with a greater leaf area index, spikelet fertility, and instantaneous water use efficiency during flowering. Strategic irrigation concentrated roots in the top 15 cm, but differences in yield between varieties under rainfed conditions were not related to root properties. It is important to consider variations in flowering time, yield potential, and drought patterns when developing rice varieties for rainfed semi-arid tropical conditions, as well as when quantifying the benefits of strategic irrigation.

Highlights

Rice (Oryza sativa L.) is predominantly grown in the tropical lowlands as a flood irrigated paddy crop mainly with indica ecotypes
Despite being considered low yielding, some adapted aerobic rice varieties can produce a high yield with a high harvest index (HI) when grown without nutrient deficiency and/or drought [1]
We conclude that acceptable rice grain yields up to 5 t/ha can be achieved with strategic irrigation when enabling early season sowing and avoidance of late season detrimental cool temperatures

Summary

Introduction

Rice (Oryza sativa L.) is predominantly grown in the tropical lowlands as a flood irrigated paddy crop mainly with indica ecotypes. In water-scarce areas in many countries, rice is grown as an upland crop (or aerobic rice) mainly with japonica ecotypes. Aerobic rice is grown in soil often kept below water saturation. Improving water productivity for rice production is a global driver for the rice industry. Non-flooded irrigation for rice production systems has been seen as an effective way of improving water productivity, when moving rice production to new regions with limited water. Despite being considered low yielding, some adapted aerobic rice varieties can produce a high yield with a high harvest index (HI) when grown without nutrient deficiency and/or drought [1].

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