Sugarcane - Bioenergy Crop Plants - page 528

Sugarcane is relatively tolerant to soil acidity but limestone application is recommended when
soil pH is below 5.5. Because of the high dry matter yields, fertilizer needs of sugarcane are rela-
tively high. The nutrient content of shoots of a crop yielding 100 t of stalks are around 100-154 kg
N, 15-25 kg P 2 O 5 , 77-232 kg K 2 O, and 14-49 kg S (various authors, compiled by Raij et al. 1997;
Cantarella et al. 2007; Rossetto et al. 2008). Fertilization of sugarcane varies widely depending
on the country, soil type, and yield potential. Sugar crops account for 7.5 million t of the NPK fer-
tilizers used in 2007-2008, representing 4.5% of the world fertilizer consumption (Heffer 2009).
It can be assumed that most of this fertilizer goes to sugarcane because sugar beet cropping area
corresponds to 0.11% of that of sugarcane worldwide (FAOSTAT 2009). In Brazil 23% of the N,
8.7% of the P, and 21% of the K fertilizer are used in sugarcane (FAOSTAT 2009). Nitrogen and
potassium are the nutrients used in largest amounts. Rates of application of N vary from 60 to 200
kg/ha (Raij et al. 1997; Rice et al. 2006). For P, up to 150 kg/ha P 2 O 5 may be applied in low fertil-
ity soils but rates may be much smaller in many regions (Hartemink 2008). The sugarcane plant
extracts large quantities of potassium and fertilization may reach, in kg/ha K 2 O, 150 in Brazil and
Australia, 175 in Costa Rica, 280 in the United States (Legendre 2001; Rice et al. 2006; Rossetto
et al. 2008b).
Despite the high internal requirements of nutrients by sugarcane, the actual chemical fertilizer
demand may be low because of recycling of plant and industrial residues because the mills and
distilleries export basically carbon, hydrogen, and oxygen in sugar and ethanol. For instance, filter
cake, which is generated at a rate of 30-35 kg (18-21 kg dry matter) per tonne of crushed fresh
stalks, contains 1-3% P 2 O 5 and is returned to the fields in natural form or composted with bagasse.
Vinasse, the fluid residue of ethanol fermentation-distillation, is produced at a rate of 10-15 L/L
ethanol and contains an average of 2 g K 2 O/L. Vinasse is applied at rates varying from 50 to 200
m 3 /ha and may supply all of the K needs of the crop that receives the residue. Ashes produced in
the furnaces contain several nutrients, including micronutrients, and are also recycled in the fields.
The relatively low amounts of N used in Brazil is taken as evidence that biological nitrogen
fixation (BNF) may play a role in nutrition of sugarcane (Urquiaga et al. 1992, 1995; Boddey et
al. 2003). Furthermore, Urquiaga et al. (1992) showed that 60-70% of the N accumulated in some
sugarcane varieties came from BNF. However, studies carried out in Australia and South Africa
failed to show that BNF was a significant source of N to sugarcane (Biggs et al. 2002; Hoefsloot
et al. 2005). Recent findings indicate that selected diazotrophic bacteria may effectively increase
yield and supply N for sugarcane (Oliveira 2006; Reis et al. 2008). Although BNF offers a promis-
ing way to decrease sugarcane dependence of N mineral fertilizers, much work remains to be done.
Nutrient recycling in the field can also be improved if leaf burning that precedes harvesting is
avoided. Manual harvesting that prevails in most of the world, especially in developing countries,
is made easy by burning the crop but nutrients such as N and S are lost by volatilization and others
are spread away with the ashes. When sugarcane is harvested unburned either manually or with a
combine machine, a thick mulch of leaves and tops, equivalent to 8-20 t/ha of dry material remains
on the soil, recycling nutrients and organic matter to the soil.
21.3 suGarcane Pests and dIseases
A number of pests and diseases attack sugarcane. Among the insects the sugarcane borer ( Diatraea
saccharalis ) is the most common, and may affect yield and quality of stalk because of the inva-
sion of fungi and bacteria through the holes opened by the borer. The control of sugarcane borer is
carried out with integrated pest management (IPM) that involves scouting of the insect population
and biological control with one of the various natural enemies including Cotesia flavipes, Lydella
minense, and Paratheresia claripalpis . Insecticides are rarely needed.
Pests that live in the soil, roots or stubble include the spittlebug Mahanarva fimbriolata that
sucks the plant, the beetle Migdolus , and several species of termites. The control involves monitor-
ing of infected areas to assess damage levels, management practices such as mechanical destruction