Murilo Mesquita Baesso

Spectral indexes for identification of nitrogen deficiency in maize

Image analysis can provide information extracted from the leaves of crops, and contribute to early identification of nutrient deficiency. The objective of this study was to recognize nutritional nitrogen (N) patterns in maize plants, at the V4 and V7 stages, using digital image analysis based on spectral indexes. The experiment was carried out in a greenhouse under hydroponic cultivation. Treatments consisted of a completely randomized design, in a 4 × 2 factorial arrangement, with four replications. The factors were constituted by the doses of N (0; 3.0; 6.0 e 15 mmol L-1) combined at V4 and V7. In each stage, digital images were taken of leaf blades, with subsequent chemical composition and image analysis. For image recognition and classification, a vector of characteristics based on the spectral indexes was used as follows: excess of green, normalized red, normalized green and red-green ratio, and the combination among them. Additionally, extracted blocks of 9 × 9, 20 × 20 and 40 × 40 pixels on original images were used. The N content in the leaf blade, the dry mass of the plants and the external critical level of N in the nutrient solution were determined for result validation, based on 90% dry matter production. Maximum the global accuracy rate for N patterns was 80 and 93% at V4 and V7, respectively. The use of combined spectral indexes provided better classification performance, and the 9 × 9 pixel image block appeared more adequate for differentiation among the doses of N.

Effect of seed-furrow openers on soybean root growth in compacted Oxisol

This study aimed to evaluate the effects of seed-furrow openers and soil compaction on parameters such as sowing quality and root growth of soybean. The experiment was conducted using a randomized blocks experimental design with split plots, with the plots arranged by compaction level (1.16, 1.20, 1.22 and 1.26 Mg m-3) and the subplots by type of furrow opener (double disk and shank type). Root growth was assessed at three depths (0.00-0.10; 0.10-0.20 and 0.20-0.30 m) in the sowing line and interrow. The sowing quality data means were compared using the Tukey test (p≤0.05), while the root growth data means were compared using the LSD test (p≤0.05). Penetration resistance increased with increasing soil compaction to a depth of 0.20 m. The sowing depth and mobilized soil area were not affected by soil compaction levels. The type of furrow opening mechanism only influenced the sowing depth, with greater depth achieved using the double disc. Neither the seed-furrow openers nor the level of soil compaction significantly influenced soybean root growth when evaluated in the sowing line. The type of furrow opening mechanism did not influence any of the evaluated parameters. Soil compaction altered soybean root growth in the interrow, but did not impede rooting. Regardless of the assessment depth in the interrow, there was a reduction in root volume, length, surface area and diameter with increased soil density. n n xa0 n n Key words: No-tillage, seeder, soil density, sowing depth, penetrometer resistance.

NOTA TÉCNICA: MAPEAMENTO DA VARIABILIDADE ESPACIAL DO BRIX EM CANA-DE-AÇÚCAR

This study proposes a method to map brix variability in sugarcane plantations. The data were collected in cane field of Usina Paineiras S.A., at Itapemirim, ES. The brix readings were collected from an area of 1.0 ha. The geostatistical analysis was carried out using software Arcgis 9.2®. The Gaussian Krig model was selected according to the method proposed in this work. A thematic map of spatial brix variability was obtained that can help sugarcane management, detecting faults and yield limitation factors.