The experiment 1 consisted to evaluate seven rotational crops plus control (fallow) grown before sugarcane was planted.

The soil is as a Typic Paleudult and was chemically characterized at different depths with samples taken after the green manures were cut but before sugarcane was planted (Table 1).

The experimental design was a randomized block with eight treatments and five replications.

The rotational crops were peanut (Arachis hypogaea L.) cv. IAC-Tatu, peanut cv. IAC-Caiapo, sunn hemp cv. IAC-1 (Crotalaria juncea L.), velvet bean (Mucuna aterrima Piper and Tracy), soybean (Glycine max L. Merrill) cv. IAC-17, sunflower (Helianthus annuus L.) cv. IAC — Uruguai, and mung bean (Vigna radiata L. Wilczek).

The green manures were sowed always in December on 7 m * 10 m size plots, with rows 0.50 m apart. The experimental area was weeded 30 d after sowing, and the weed residues were left on the soil surface.

During seed filling, the plants used as green manure were manually cut and spread on the soil covering the entire plot surface in pieces less than 0.25 m and left there for six months. Peanut, soybean, sunflower and mung bean were harvested after physiological maturation for the grain yield, and the remaining plant parts were cut and spread on the soil. Biomass production of the rotational crops was evaluated in 1 m2 of the plot area.

At the harvest stage, the roots of each rotational crop were sampled in order to evaluate the natural colonization level of arbuscular mycorrhizal fungi (AMF). The colonization percentage was estimated using the root coloration technique according to [21]. The percentage of colonization by AMF was estimated by counting the roots’ stained portions using a reticular plate under a microscope following the procedures described by [22].

To evaluate sugarcane stalk yield 2-m sections of each of the three central rows were cut and weighed.

Ten successive stems were separated from each plot for the technological evaluation of the Brix, pol, and total recovered sugar [23]. Sugar yield, expressed in terms of tons of pol per hectare (TPH), was estimated with the stem yield and technological analysis data.

The economic balance considered the costs of production and revenues of the rotational crops as well as three harvests of sugarcane. The basic costs of production of sugarcane (including land preparation, seed stalk, fertilizer, herbicides feedstock and application, and harvesting) were the average of the 2004, 2005, and 2006 prices, based on an average stalk yield of 70 t ha-1. For the control treatment, which did not include the crop rotations, the cost of production of sugarcane was estimated as U$ 3,111 ha-1. The costs of production of the green manures crotalaria and velvet beans, U$ 100 ha-1, include seeds, planting, and cutting. For the grain crops, the costs of grain harvesting and of chemicals needed for phytosanitary control were added: sunflower (U$ 422 ha-1), peanut cv. IAC-Tatu (U$ 1,289 ha-1), Peanut cv. IAC-Caiapo (U$ 1,480 ha-1), mung bean (U$ 2,007 ha-1) and soybean (U$ 513 ha-1). The sales prices of grain and cane stalks for the period between 2004 and 2006 (according to a database of the Institute of Agricultural Economics of the Sao Paulo State Secretary of Agriculture) were: sugarcane stalks, U$ 17.56 t-1; sunflower, U$ 178 t-1; peanut cv. IAC-Tatu, U$ 260 t-1; peanut cv. IAC-Caiapo, U$ 260 t-1; soybean, U$ 197 t-1; and mung bean, U$ 2,222 t-1. Mung bean is not sold as a commodity but as a specialty crop; its prices are highly variable, and the market for it is relatively small; therefore, the data on the economical return for mung bean must be taken with care.