Managing yield decline in sugarcane cropping systems

This paper summarises the results from ten years of yield decline research carried out by the Sugar Yield Decline Joint Venture in the Australian sugar industry. The research concludes that, although the ultimate expression of yield decline may be through adverse effects of pathogens on sugarcane root systems, yield decline is a complex issue caused by a number of factors being out of balance in the sugarcane cropping system. Soil degradation has been the result of the long-term sugarcane monoculture and how it has been practiced. Specific research has shown that the long-term monoculture, uncontrolled traffic from heavy machinery and excessive tillage along with practices that deplete organic matter all contribute to yield decline. It is argued that changes to the cropping system that will conserve organic matter, break the monoculture, control traffic and minimize tillage are the most appropriate ways to combat yield decline. The technology is now available to incorporate these changes into the cropping system and a more sustainable, profitable and environmentally responsible cropping system is proposed. The proposed system is not prescriptive and many acceptable variations will be just as suitable providing the basic principles of organic matter conservation, breaking the monoculture, controlling traffic and minimizing tillage are no compromised

Estimating Surface Wetness on Plants

Plant surface (leaf, stem, petiole, etc) wetness or leaf wetness is an important agricultural weather variable for the prediction of plant diseases (Yarwood, 1978). The estimation of surface wetness has received considerable attention from a diverse group of scientists but unfortunately, no standard for measuring surface wetness has been widely accepted. Since surface wetness is not a true meteorological variable, as is temperature or precipitation, its measurement has not been routinely made as part of a general observation program by most national meteorological agencies. The main problem of not observing surface wetness on a routine basis has been the lack of agreement about a standard sensor design and protocol for the use of sensors. In addition, most sensors measure surface wetness indirectly and have different physical properties. In order for a sensor to represent a particular crop, plant organ, or environment, the sensor should be calibrated with visual observations of surface wetness. Unfortunately, the collection of visual observations is labor intensive and difficult, since there is no universally accepted definition for plant surface wetness. In this chapter, we will attempt to define surface wetness in physical terms and review methods for determining surface wetness. We also will consider solutions to the lack of surface wetness standardization from both a measurement and simulation perspective. And finally, we will also recommend the most suitable protocols for estimating surface wetness

Reduced tillage planting and the long-term effect on soil-borne disease and yield of sugarcane (Saccharum inter-specific hybrid) in Queensland, Australia

Pachymetra is a major root disease of sugarcane causing yield and economic loss in the Australian sugar industry, with planting of resistant cultivars being the control strategy practiced by the industry. To adopt reduced tillage and not be affected by soil compaction in the old inter-row it is necessary to re-plant into the old crop row. The hypothesis was: would reduced tillage and planting in the old crop row in conjunction with rotation of resistant and susceptible cultivars minimise the effect of this soil borne disease on crop yield? To facilitate the adoption of reduced tillage in the Australian sugar industry randomized block field experiments were undertaken on Alfisols, near Tully, north Queensland and Bundaberg, south Queensland, Australia comparing reduced tillage with conventional cultivation for planting sugarcane Results showed that, providing Pachymetra resistant cultivars were used, there was no yield reduction with reduced tillage. Levels of Pachymetra remained close to the threshold of 40,000 spores per kilogram of soil under the resistant cultivar but increased under the susceptible cultivar as the crop cycle progressed. Planting a resistant cultivar after a susceptible cultivar or vice versa did not affect cane yield. Over a crop cycle of a plant and three ratoons at Bundaberg the average yields of the susceptible and resistant cultivars were 114 and 89 t/ha, respectively, an increase of 28% with the resistant cultivar. Similarly at Tully the average yield for the resistant and susceptible cultivar was 75 and 69 t/ha, a 9% increase in yield with the resistant cultivar.\ud \ud Earthworm numbers recovered quicker under reduced tillage compared with conventional tillage suggesting that in the medium to long-term soil health will benefit by the adoption of reduced tillage for planting sugarcane. Reduced tillage did not affect the population of Pratylenchus zeae and increased the number of Rotylenchus nematodes under stool sprayout compared with all other tillage treatments.\ud \ud It is concluded that sugarcane cultivars are available that allow the adoption of reduced tillage in Pachymetra areas without compromising yield

Effect of breaks on sugarcane growth: relations between glasshouse and field studies

The effects of varying types and duration of breaks (other crops, pastures or bare fallows) and soil fumigation on subsequent growth of sugarcane crops were investigated in a series of five field experiments in Australia. Results from the first series of test plantings have shown breaks can produce significant effects on sugarcane growth and yield - at least as large as those from soil fumigation. These responses have generally been characterised by marked differences in shoot establishment and early growth in the first 70-90 days. Glasshouse studies conducted using soil from the same sites showed significant (P<0.05) effects of break history on early shoot growth (35-45 days) at four of the five sites. Positive responses to soil fumigation were also recorded at three of the five sites. Fumigation with methyl bromide produced minimal effects on early growth in soil that had been bare fallowed (-15% to 2%), or soil that had been fumigated in the field (-4% to 29%). Fumigation of soil from continuous cane treatments typically increased early cane growth by 25-30%. Most breaks had effects intermediate between the control and the bare fallow - both in early growth and response to fumigation. Shoot dry matter in unfumigated soil in the short-term glasshouse studies was strongly correlated with field shoot numbers at 70-90 days after planting and with dry matter production after 8 months. Correlations were either much weaker, or had disappeared entirely, by final harvest due to unexplained differences in growth rates among treatments during the final 4 months. Growth in fumigated break soil in the glasshouse was not correlated significantly with growth in the field, indicating that biotic factors were associated with these early growth differences in the field. These findings suggest that short duration pot experiments may be a useful research tool to study the biotic effects on early growth of sugarcane. This will provide more rapid experimental cycles and significant cost savings compared to field studies. However, other evidence suggests that results from such studies will not necessarily be a good indicator of ultimate crop yield

Biological studies of soils in paired old and new land sites growing sugarcane

The growth of sugarcane in soils from land monocultured with sugarcane, and from land which had either never been cropped with sugarcane, or just recently cropped, was compared under glasshouse conditions. In general, cane growth in new land soils was greater than in monocultured soil (shoot growth 7.4%, root growth 21.4%). Responses to soil pasteurisation were investigated in some soils and were greater in monocultured soils suggesting that root growth constraints were larger in the monocultured soil (210% response in monocultured soils v. 64% in new land soils). Assays for sugarcane root pathogens suggested that Pachymetra chaunorhiza was a major contributor to the old/new land growth responses, but it is unlikely that Pythium spp. were factors in the growth differences. Monitoring of other groups of organisms in soil from one site suggested that sugarcane monoculture may affect populations in the broader biological community

Management practices to improve soil health and reduce the effects of detrimental soil biota associated with yield decline of sugarcane in Queensland, Australia

Yield decline (YD) of sugarcane is a widespread problem throughout the Australian sugar industry. It is defined as "the loss of productive capacity of sugarcane-growing soil under long-term monoculture". Factors contributing to YD are the monoculture itself, excessive tillage of the soil at planting and severe soil compaction resulting from the use of heavy machinery during the harvesting operation. Collectively, these crop management practices have led to the development of sugarcane-growing soils that are low in organic C and cation exchange capacity, have a high bulk density and have a low microbial biomass. This in turn is associated with a build up of populations of detrimental soil organisms, which affect the growth and health of the sugarcane root system. Significant yield increases have been demonstrated following pasteurization or fumigation of the soil or treatment of the soil with fungicides or nematicides. Several detrimental soil organisms associated with YD have been identified, including a fungal root pathogen (Pachymetra chaunorhiza) and the lesion nematode (Pratylenchus zeae). Experimental evidence, however, suggests there are many other unidentified detrimental soil organisms associated with YD. In order to circumvent YD, major changes to the cane cropping system need to be considered. Different rotation breaks (sown pasture, alternate crops, bare fallow) were evaluated for their impact on soil health and the composition of the community of organisms in soil previously under cane monoculture. Despite the breaks having different effects on populations of beneficial soil biota, all breaks reduced populations of known detrimental soil biota and significantly increased the yield of the following cane crop. A single legume-based break crop appeared to be sufficient to capture the majority of these benefits. Other possible management options including the use of organic amendments and minimum tillage techniques are discussed