Weed Suppression, Biomass and Nitrogen Accumulation in Mixed-Species and Single-Species Cover Crops in a Tropical Sugarcane Fallow

Lawrence Di Bella,Megan Zahmel,Lukas Van Zwieten,Terry J Rose

doi:10.3390/agriculture11070640

Lawrence Di Bella, Megan Zahmel + Show 2 more

Open Access

https://doi.org/10.3390/agriculture11070640

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Abstract

While mixed-species cover crops are gaining worldwide popularity, their utility in the ‘plough-out’ period in tropical sugar cane systems has not been investigated. Field trials investigating weed suppression (one season only), biomass production and nitrogen accumulation of single-species and mixed-species cover crops were conducted over two seasons on a commercial sugarcane farm in the Australian tropics. Mixed-species cover crops showed strong weed suppression, and were among the top treatments for biomass production each year, but did not yield the highest biomass in either season. Sunn hemp (Crotalaria juncea cv. Global sunn) produced the most biomass in the drier-than-average 2016–2017 season (>10 t dry matter ha−1), while soybean (Glycine max cv. Leichardt) produced the most biomass (5.3 t dry matter ha−1) in the wetter-than-average 2018–2019 season, highlighting the influence of seasonal conditions on species’ biomass production. The inclusion of multiple species in a short-term cover crop in the tropics where extreme weather events can occur can thus be seen as a risk mitigation strategy given the risk of failure of any given species in a given season.

Highlights

Sugarcane (Saccharum officinarum) is cultivated on an estimated 27 million ha across the globe [1], predominantly in tropical regions
Sugarcane in the Australian tropics is typically harvested annually with four or more ratoon crops grown before cane is removed [2]
The continual production of sugarcane in the same field over time has led to observations of yield decline, which appears to be related to a decline in soil health and build-up of pathogens associated with the sugarcane monoculture [4]

Summary

Introduction

Sugarcane (Saccharum officinarum) is cultivated on an estimated 27 million ha across the globe [1], predominantly in tropical regions. At the start of a production cycle in Australia, sugarcane is established from vegetative propagules known as ‘billets’ or ‘setts’ and the first crop is termed ‘plant cane’. This crop is typically harvested after a year and the sugarcane plant regrows from the roots and crown (‘stool’), remaining in the soil to produce a ’ratoon crop’. Sugarcane in the Australian tropics is typically harvested annually with four or more ratoon crops grown before cane is removed [2]. While ratoon crops can have lower yields than plant cane crops, the cost of production is typically lower [3]. The continual production of sugarcane in the same field over time has led to observations of yield decline, which appears to be related to a decline in soil health and build-up of pathogens associated with the sugarcane monoculture [4]

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