**3.1.4 Effect of the air-assistance delivery system on soybean productivity**

The influence of an air-assisted delivery system on soybean productivity, var. Conquista, 2006/07 and 2007/08 seasons are shown in Figure 4. The spraying treatments used to control *P. pachyrhizi* fungus were applied on soybean plants (R2 and R5.2 growth stages) using a triazole + strobilurin spray mixture and volume rates between 120 at 150 L ha-1. The data of soybean crop productivity after two sprayings with different technologies was submitted to a variance analysis and the averages were compared by Tukey's test (p<0.05).

Fig. 4. Effect of treatments: control (not treated); air-assistance delivery system at zero (without air), 9, 11 and 29 km h-1 air speed; rotating nozzle-LVO with a third part of spray volume (40L ha-1) on soybean productivity. The Conquista variety was used in the 2006/07 and 2007/08 agricultural seasons. Botucatu, SP, Brazil (2006/07 - Christovam et al. 2010b; 2007/08\* - Prado et al. 2010; 2007/08\*\* - Christovam et al. 2010a).

In general, this technology provided higher productivity, in relation to that with conventional spraying (without air) and control (not treated). A higher increase in soybean productivity was obtained with maximum air speed generated by the fan (29 km h-1). The

air assistance constituted an optional implement on the boom sprayers that can increase up 30% the equipment cost in relation to conventional sprayers which do not have this technology. Although the use of this technology should not be recommended on soils without vegetation or even on early stages due to the smaller foliar area. This method provides several advantages that have been mentioned before.

#### **3.1.5 Air assistance and spray drift**

128 Soybean Physiology and Biochemistry

Fig. 3. Air-assisted sleeve boom sprayer in the following operation modes: A – conventional spraying (without air); B – spraying with air assistance at 0º (vertical) and C – spraying with air assistance angled at 30º forward to the displacement of the tractor-sprayer assembly on

The influence of an air-assisted delivery system on soybean productivity, var. Conquista, 2006/07 and 2007/08 seasons are shown in Figure 4. The spraying treatments used to control *P. pachyrhizi* fungus were applied on soybean plants (R2 and R5.2 growth stages) using a triazole + strobilurin spray mixture and volume rates between 120 at 150 L ha-1. The data of soybean crop productivity after two sprayings with different technologies was submitted to a variance analysis and the averages were compared by Tukey's test (p<0.05).

<sup>b</sup> <sup>c</sup> <sup>b</sup>

Fig. 4. Effect of treatments: control (not treated); air-assistance delivery system at zero (without air), 9, 11 and 29 km h-1 air speed; rotating nozzle-LVO with a third part of spray volume (40L ha-1) on soybean productivity. The Conquista variety was used in the 2006/07 and 2007/08 agricultural seasons. Botucatu, SP, Brazil (2006/07 - Christovam et al. 2010b;

In general, this technology provided higher productivity, in relation to that with conventional spraying (without air) and control (not treated). A higher increase in soybean productivity was obtained with maximum air speed generated by the fan (29 km h-1). The

b

2006/07 2007/08\* 2007/08\*\* **Season**

Control without air 9 km/h 11 km/h 29 km/h

a

a

**LVO**

ab <sup>a</sup>

a

**A B C** 

ab <sup>a</sup>

b

a

a

2007/08\* - Prado et al. 2010; 2007/08\*\* - Christovam et al. 2010a).

a

**3.1.4 Effect of the air-assistance delivery system on soybean productivity** 

soybean crop.

**Yield kg/h**

**a**

Air assistance in the spraying sleeve boom significantly improves the penetration of spraying, especially in high cultures and high leaf density, such as potato, in addition to reducing drift (Koch, 1997). However, these effects were not observed when air-assisted spraying is done on bare soil or plants in the first stages of growth. Also, according to Matthews (2000), air-assisted spraying penetration is better when compared to conventional spraying on wide-leaf cultures, such as cotton. In Holland, tests with the air-assisted sprayer Twin (Hardi) have been carried out on potato cultivation. Generally, air assistance reduced drift by sedimentation by 50% and the air-carried drift by 75%. In Holland, the accepted drift percentage by sedimentation is 8-10% for a distance of 1.5 to 2.0 metres from the boom, and around 0.2% for 5.0 to 6.0 metres intervals. The recommendation for making spraying in Holland is with a wind speed less than 5.0 m sec-1. In Germany, the accepted drift values by sedimentation when applying phyto-sanitary products range from 0.6 to 0.1%, respectively, for distances of 5.0 to 30.0 metres from the spraying sleeve boom (Jorgensen & Witt, 2000). Considering the drift limits accepted for spraying in Germany, the safe distance for applying near water channels (irrigation/draining) in that country is 10.0 metres for 80% of the herbicides approved for use, and 20.0 metres for other herbicides. France and Belgium comply with the drift limits accepted in Germany. Artificial targets have been also used by the Morley Research Centre for simulating venomous plants in the sugar beet. The variations in the deposit values for air-assisted spraying were lower when compared to those achieved with the conventional sprayer (Taylor & Andersen, 1997). These authors have also demonstrated the influence of air assistance on drift percentage reduction compared with conventional application (without air), by obtaining 90, 84, 83, 76, 68 and 61%, respectively, when spraying barley, bean, pea, Brussels sprouts, lettuce and leek, with fine droplets. Nowadays, studies involving computer models aim at clarifying the relationship among the air released drift risk and deposit on target. Preliminary studies have shown that the increase of the displacement speed with air-assisted sprayers may reduce drift, but provide lower evenness in the target culture treatment (Miller, 1997). However, aiming at reducing the application volume, Nordbo (1992) has demonstrated lower variation and improved deposit by using air assistance. The density, architecture, cuticle type (pilose, glabrous and waxy) and growth stage of the vegetal species in the area are factors influencing phyto-sanitary control efficiency when using air-assisted sleeve boom sprayers. Fine droplets provide larger deposits on plants, especially monocotyledons, but are very susceptible to drift. Their penetration capacity in cultures is small, and then the loss to the soil must be limited. Therefore, air assistance enables using fine droplets more efficiently, by reducing the drift and increasing the deposits on the target, in addition to providing higher penetration of these droplets in cultures with higher leaf density, and reducing losses to the soil (Jorgensen & Witt, 1997). On the other hand, coarse droplets generally provide good drift control. In dicotyledons, the deposits do not depend only on droplet size (Nordbo, 1992). Unlike the results with smaller diameter droplets, coarse droplets provide significantly lower deposits on vertical surfaces (monocotyledons), and especially in the first growth stages, by increasing the loss to soil proportionally to their size (Jorgensen & Witt, 1997). In vegetables, where droplet retention is limited by the presence of waxy layers on the cuticle, further studies are required, especially with air-assisted spraying, in order to evaluate the application quality (Koch, 1997). In the absence of vegetation (bare soil), air assistance may increase drift and deflect the air from the sprayer by the soil, unlike the effect which occurs in the presence of vegetation, with the impact of droplets on the leaf surface (Matthews, 2000).
