A field experiment was conducted from June to December
2002, at the experimental area of Plant ScienceDepartment of the
Escola Superior de Agricultura de Mossoro´ (ESAM), RN, Brazil
(378200W longitude and 58110S latitude at an altitude of 18 m
above mean sea level). The experimental site is located in a semiarid
region, the climate is a BSwh type, i.e., very dry, with two
seasons, a dry season from June to January and awet season from
February to May (Carmo Filho and Oliveira, 1991), with mean
annual rainfall of 674 mm (Carmo Filho and Oliveira, 1989).
During the experiment, the average maximum temperature from
June to December was 33–37 8C with a mean of 34.1 8C. The
average minimum temperature was 19–23 8C with a mean of
20.6 8C. The relative humidity was between 62 and 86.6%, with
monthly wind speed between 2.7 and 6.0 m/s,mean insolation of
280.4 h/month and evapotranspiration in the period between 4.2
and 10.8 mm/day. The soil was a eutrophic red-yellow ultisol
(ERYU), which had been left fallow for 6 years. Before its
preparation, samples were taken at a depth of 0–20 cm and
submitted to chemical analysis which led to the following results
per soil dry weight: pH 7.6 (in water); P = 33mg kg1;
K+ = 1.56 mmolc kg1; Ca2+ = 33.8 mmolc kg1; Mg2+ =
5.6 mmolc kg1; Na+ = 0.56 mmolc kg1; Mn2+ = 7.8 mg kg1;
1; Cu2+ = 0.3 mg kg1; Zn2+ = 0.8 mg kg1; Fe3+ = 5 mg kg1;
B3+ = 0.18 mg kg1. The soil was then plowed at 30 cm depth
and harrowed. Before planting, animal traction was used to
prepare the soil and hills were created with a hoe.