Maize production as affected by sowing date, plant density and row spacing in the Bolivian Amazon
The traditional cropping system widespread in the Department of Pando (Bolivian Amazon) is the slash and burn methodology. The main crops sowed soon after the slash are maize, rice, cassava and common beans. Two separate field experiments (carried out in 2008-2009) were carried out to determine the agronomic responses of maize to sowing date, plant population and row width. For the first experiment a split-plot design was used. Maize cultivar (Bayo Blando and Perla Pandino) was considered as main plots and the date of sowing as subplots. For the second experiment a split-split-plot design was used. Row spacing (0.5, 0.7 and 0.9 m) was considered as main plot, maize cultivar (Cubano Amrarillo and Perla Pandino) as subplots, and plant density (5.0, 7.5 and 10 plant m-2) as sub-subplots. A significant reduction of grain yield was observed as the date of sowing (DS) delayied. Yield reduction of the second DS compared to the first, was 85 and 45% for Perla Pandino and Bayo Blando. The importance of plant density as a function of the correct row spacing is clearly shown. With the row spacing in use in the considered area (0.9 m) and with the narrowest (0.5 m), the best yields were obtained with 10 plants m-2 (5.5 t ha-1). The following conclusions can be drawn from the present study: 1. A delay in the sowing date for maize by 15-20 days (compared to sowing ??immediately after the cutting of the virgin forest or the secondary forest) strongly reduces grain production. The cultivar Perla Pandino was the most susceptible with a reduction of 85%. Late sowing of maize (mais de socorro), is suitable only if intercropped with other crops in order to protect the soil from erosion. Traditionally, rice and cassava are intercropped with maize, even if common beans or a legume cover crop would be more advisable. 2. The density of maize may be increased up until 10 m-2 in order to achieve the most productive results by using row spacings of 0.5 e 0.9 m, respectively, depending on the genotypes used. For varieties, with a reduced height such as Perla Pandino, it is possible to use a more narrow row spacing, whilst for tall plants, over 2 m, such as Cubano Amarillo, a wider row spacing is recommended.