Effect of a sugarcane-legume cropping rotation system on cane yield under irrigated conditions in Côte d'Ivoire
To find an alternative to the use of nitrogenous fertilizers in sugarcane cultivation, this study was initiated in order to improve soil fertility and sugarcane yield by growing legumes. The trials were carried out on-farm according to split-splot design in ferké 1 sugar bowl northern Côte d’Ivoire. The main factor was the cropping system (4 levels) and the subsidiary factor was the treatment with urea (3 levels). On the experimental plot, two legumes fallows (Soybean and Lablab) were grown in rotation with sugarcane. The sugarcane yields obtained were compared with those of the conventional system and those obtained after natural fallow using only nitrogenous fertilizers. In main crop as well as ratoon crop, sugarcane yields were statistically identical for all four cropping systems. Nevertheless in ratoon crop, the effect of treatment with urea was significant. Thus, the input of half-dose of urea was the best treatment with urea. During the two years of cultivation, sugarcane yields were statistically different; the effect of years being significant on sugarcane yield, with the first ratoon as the best crop year with an average yield of 58.4 Tc/ha. Legume cultivation as a preceding crop has enabled subsequent canes to provide yields that are statistically identical to those of other cropping systems that use only nitrogenous fertilizer. It has also helped to halve the use of urea in ratoon crop and finally to obtain higher sugarcane yields in ratoon crop.
To find an alternative to the use of nitrogenous fertilizers in sugarcane cultivation, this study was initiated in order to improve soil fertility and sugarcane yield by growing legumes. The trials were carried out on-farm according to split-splot design in ferké 1 sugar bowl northern Côte d’Ivoire. The main factor was the cropping system (4 levels)
and the subsidiary factor was the treatment with urea (3 levels). On the experimental plot, two legumes fallows (Soybean and Lablab) were grown in rotation with sugarcane. The sugarcane yields obtained were compared with those of the conventional system and those obtained after natural fallow using only nitrogenous fertilizers. In main
crop as well as ratoon crop, sugarcane yields were statistically identical for all four cropping systems. Nevertheless in ratoon crop, the effect of treatment with urea was significant. Thus, the input of half-dose of urea was the best treatment with urea. During the two years of cultivation, sugarcane yields were statistically different; the effect of years being significant on sugarcane yield, with the first ratoon as the best crop year with an average yield of 58.4 Tc/ha. Legume cultivation as a preceding crop has enabled subsequent canes to provide yields that are statistically identical to those of other cropping systems that use only nitrogenous fertilizer. It has also helped to halve the use of urea in ratoon crop and finally to obtain higher sugarcane yields in ratoon crop.
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Int. J. Agr<strong>on</strong>. Agri. R.<br />
Introducti<strong>on</strong><br />
Sugar<strong>cane</strong> (Saccharum <str<strong>on</strong>g>of</str<strong>on</strong>g>fic<strong>in</strong>arum L.) is a perennial<br />
grass from the Poaceae family. He is a highly<br />
cultivated plant <strong>in</strong> the world because <str<strong>on</strong>g>of</str<strong>on</strong>g> its<br />
importance <strong>in</strong> terms <str<strong>on</strong>g>of</str<strong>on</strong>g> agri-food, ec<strong>on</strong>omy and<br />
energy. It is generally cultivated <strong>in</strong> the tropical and<br />
subtropical regi<strong>on</strong>s, ma<strong>in</strong>ly for the exploitati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> sugar<br />
c<strong>on</strong>ta<strong>in</strong>ed <strong>in</strong> its stems. Indeed, the latter can have<br />
sacchar<strong>in</strong>e c<strong>on</strong>tent up to 19% each (Péné et al., 2012).<br />
World c<strong>on</strong>sumpti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> sugar is c<strong>on</strong>stantly <strong>in</strong>creas<strong>in</strong>g,<br />
hence the need for <strong>in</strong>creased sugar producti<strong>on</strong>. Thus,<br />
the 2014-2015 sugar seas<strong>on</strong> ended with a sugar<br />
producti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> 182.1 Mt, that is, an <strong>in</strong>crease <str<strong>on</strong>g>of</str<strong>on</strong>g> 0.22 Mt<br />
more than the previous seas<strong>on</strong> (FAO, 2015). Apart<br />
from beet and sweeteners, <str<strong>on</strong>g>sugar<strong>cane</strong></str<strong>on</strong>g> al<strong>on</strong>e accounts<br />
for 75% <str<strong>on</strong>g>of</str<strong>on</strong>g> world sugar producti<strong>on</strong>.<br />
In <strong>Côte</strong> <strong>d'Ivoire</strong>, its cultivati<strong>on</strong> is largely ensured by<br />
two private companies (SUCAF-CI and<br />
SUCRIVOIRE) over a distributi<strong>on</strong> area <str<strong>on</strong>g>of</str<strong>on</strong>g> more than<br />
25000 ha (<strong>under</strong> <str<strong>on</strong>g>sugar<strong>cane</strong></str<strong>on</strong>g> cultivati<strong>on</strong>) located <strong>in</strong> the<br />
northern and west-central part <str<strong>on</strong>g>of</str<strong>on</strong>g> the country<br />
(Kouamé et al., 2009). With an annual nati<strong>on</strong>al <strong>yield</strong><br />
estimated at more than 180,000 t, it succeeds <strong>in</strong><br />
cover<strong>in</strong>g domestic demand for sugar and makes <strong>Côte</strong><br />
<strong>d'Ivoire</strong> the largest sugar producer <str<strong>on</strong>g>of</str<strong>on</strong>g> the West<br />
African Ec<strong>on</strong>omic and M<strong>on</strong>etary Uni<strong>on</strong> (WAEMU)<br />
(Péné and Kehe, 2005). Despite its socio-ec<strong>on</strong>omic<br />
importance <strong>in</strong> <strong>Côte</strong> <strong>d'Ivoire</strong>, <str<strong>on</strong>g>sugar<strong>cane</strong></str<strong>on</strong>g> cultivati<strong>on</strong><br />
faces many difficulties. It is c<strong>on</strong>fr<strong>on</strong>ted, <strong>on</strong> the <strong>on</strong>e<br />
hand, to biotic c<strong>on</strong>stra<strong>in</strong>ts due to viruses, stem borers<br />
such as Eldana sacchar<strong>in</strong>a Walker, bacteria such as<br />
Xanthom<strong>on</strong>as albil<strong>in</strong>eans and fungi such as<br />
Sporisorium scitam<strong>in</strong>eum, resp<strong>on</strong>sible for anthrax<br />
(Kouamé et al., 2010). On the other hand, it is fac<strong>in</strong>g<br />
a decl<strong>in</strong>e <strong>in</strong> soil biological fertility due to <str<strong>on</strong>g>sugar<strong>cane</strong></str<strong>on</strong>g><br />
m<strong>on</strong>oculture <str<strong>on</strong>g>system</str<strong>on</strong>g>s that have been carried out for<br />
more than 30 years <strong>in</strong> the different sugar complexes<br />
(Maubouss<strong>in</strong>, 1988; Mari<strong>on</strong>, 2000). All these factors<br />
play a very important role <strong>in</strong> the reducti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
<str<strong>on</strong>g>sugar<strong>cane</strong></str<strong>on</strong>g> <strong>yield</strong>s <strong>in</strong> the sugar complexes <str<strong>on</strong>g>of</str<strong>on</strong>g> the<br />
country (Péné et al., 2012). In order to <strong>in</strong>crease<br />
<strong>yield</strong>s, <strong>in</strong>tegrated c<strong>on</strong>trol (chemical or biological) <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
the different pathogens, the improvement <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
irrigati<strong>on</strong> <str<strong>on</strong>g>system</str<strong>on</strong>g>s and <str<strong>on</strong>g>cropp<strong>in</strong>g</str<strong>on</strong>g> <str<strong>on</strong>g>system</str<strong>on</strong>g>s, the use <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
selected resistant and efficient varieties and m<strong>in</strong>eral<br />
fertilizati<strong>on</strong> (nitrogenous), are popularized methods<br />
(Kouamé et al., 2012, Yanayana et al., 2012). These<br />
different methods c<strong>on</strong>sist <strong>in</strong> phytosanitary treatments<br />
(preventive or curative), <strong>in</strong> the use <str<strong>on</strong>g>of</str<strong>on</strong>g> new varieties<br />
hav<strong>in</strong>g higher sugar c<strong>on</strong>tent, capable <str<strong>on</strong>g>of</str<strong>on</strong>g> tolerat<strong>in</strong>g<br />
partially or totally drought and the c<strong>on</strong>t<strong>in</strong>uous or<br />
fracti<strong>on</strong>ated supply <str<strong>on</strong>g>of</str<strong>on</strong>g> m<strong>in</strong>eral fertilizers <strong>in</strong> <str<strong>on</strong>g>sugar<strong>cane</strong></str<strong>on</strong>g><br />
plantati<strong>on</strong>s (Péné et al., 2012, Yanayana et al., 2012).<br />
In additi<strong>on</strong> to these methods, the <strong>in</strong>troducti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
Legumes between two <str<strong>on</strong>g>sugar<strong>cane</strong></str<strong>on</strong>g> crop cycles might be<br />
an effective means <str<strong>on</strong>g>of</str<strong>on</strong>g> soil biological fertilizati<strong>on</strong>. This<br />
would then provide good <strong>yield</strong>s, but also protect the<br />
soil by mitigat<strong>in</strong>g the use <str<strong>on</strong>g>of</str<strong>on</strong>g> <strong>in</strong>puts. In fact, <str<strong>on</strong>g>legume</str<strong>on</strong>g>s<br />
ensure, <strong>in</strong> associati<strong>on</strong> with Rhizobia bacteria, the<br />
fix<strong>in</strong>g <str<strong>on</strong>g>of</str<strong>on</strong>g> 65 milli<strong>on</strong> t<strong>on</strong>s <str<strong>on</strong>g>of</str<strong>on</strong>g> atmospheric nitrogen that<br />
they release <strong>in</strong>to the soil for the benefit <str<strong>on</strong>g>of</str<strong>on</strong>g> subsequent<br />
plants (Vance and Eardly, 2003). It is <strong>in</strong> this c<strong>on</strong>text<br />
that these crop <str<strong>on</strong>g>rotati<strong>on</strong></str<strong>on</strong>g> trials with these two <str<strong>on</strong>g>legume</str<strong>on</strong>g>s<br />
were <strong>in</strong>itiated so as to see their effects <strong>on</strong> <str<strong>on</strong>g>sugar<strong>cane</strong></str<strong>on</strong>g><br />
<strong>yield</strong>. The overall objective <str<strong>on</strong>g>of</str<strong>on</strong>g> this study was to<br />
improve soil fertility and <str<strong>on</strong>g>sugar<strong>cane</strong></str<strong>on</strong>g> <strong>yield</strong> through the<br />
cultivati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> two <str<strong>on</strong>g>legume</str<strong>on</strong>g> species.<br />
Material and methods<br />
Descripti<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> the expérimental site<br />
The study was carried out at the Ferké 1 stati<strong>on</strong><br />
located at the SUCAF-CI sugar complex (Fig. 1). The<br />
stati<strong>on</strong> is located <strong>in</strong> the southwest <str<strong>on</strong>g>of</str<strong>on</strong>g> the city <str<strong>on</strong>g>of</str<strong>on</strong>g><br />
Ferkessédougou <strong>in</strong> the regi<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> Tchologo, <strong>in</strong><br />
northern <strong>Côte</strong> <strong>d'Ivoire</strong> between 9°35 north latitude<br />
and 5°12 west l<strong>on</strong>gitude at 323 m altitude. It is 610<br />
km far from the city <str<strong>on</strong>g>of</str<strong>on</strong>g> Abidjan and is close to the<br />
borders <str<strong>on</strong>g>of</str<strong>on</strong>g> Burk<strong>in</strong>a Faso and Mali at 80km and<br />
110km, respectively. The climate <str<strong>on</strong>g>of</str<strong>on</strong>g> the z<strong>on</strong>e is dry<br />
tropical characterized by two seas<strong>on</strong>s. One so-called<br />
dry seas<strong>on</strong> extends from November to April and the<br />
other, the wet <strong>on</strong>e, extends from May to October. The<br />
dry seas<strong>on</strong> is characterized by a dry w<strong>in</strong>d, the<br />
harmattan (mid-November to late January), annual<br />
temperatures go<strong>in</strong>g bey<strong>on</strong>d 26°C and a relative<br />
humidity <str<strong>on</strong>g>of</str<strong>on</strong>g>ten reach<strong>in</strong>g 35%. This dry seas<strong>on</strong> tends<br />
to ensure a good maturati<strong>on</strong> <str<strong>on</strong>g>of</str<strong>on</strong>g> <str<strong>on</strong>g>sugar<strong>cane</strong></str<strong>on</strong>g>. Ra<strong>in</strong>fall is<br />
unimodal and ra<strong>in</strong>s are c<strong>on</strong>centrated <strong>in</strong> the August-<br />
September <strong>in</strong>terval, with annual values <str<strong>on</strong>g>of</str<strong>on</strong>g> 1200 mm.<br />
Bey<strong>on</strong>d this poor ra<strong>in</strong>y seas<strong>on</strong>, irrigati<strong>on</strong> <str<strong>on</strong>g>system</str<strong>on</strong>g>s<br />
Kouamé et al. Page 2