The objective of this work was to evaluate the use of plant height as a calibration variable for improving indirect measurements of the leaf area index (LAI). Three experiments were conducted with different crops - corn (Zea mays), soybean (Glycine max), and sugarcane (Saccharum officinarum) -, to compare the performance of the LAI measured indirectly (LAIind) and corrected by the calibration variable with the LAI measured directly (LAIref). Without the proposed correction, the LAIind tended to be overestimated by 20%, on average, compared with the LAIref, for the three crops. After crop height was used to adjust the LAIind, a strong positive relationship was observed between the LAIref and the corrected LAIind (R2 = 0.96); overestimation was reduced to 4% and the root-mean-square error decreased to 0.35 m2 m-2. The variable canopy height is promising for the correction of the LAI of the soybean, corn, and sugarcane crops.

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The reduction of sugarcane interrow spacing has the potential to increase crop yield, but research results concerning sugarcane cultivation in Brazil and worldwide remain inconclusive. Therefore, the objective of this review was to evaluate the influence of interrow spacing on the stalk fresh yield (SFY) of sugarcane and to identify the most appropriate interrow spacing in different climates and water regimes (irrigated or rainfed). In this study, a broad review of published studies was conducted to gather experimental data and evaluate the influence of interrow spacing on sugarcane SFY. A total of 28 relevant studies was used, including 170 field experiments in nine countries. Field experimental data were grouped on the basis of similarity of climate, using hierarchical cluster analysis for rainfed and irrigated experiments. Analysis of variance was used to evaluate whether there was a variation between the SFY values, and Tukey tests were applied to compare the SFY means for each interrow spacing. The results indicated that SFY significantly increased as interrow spacing was reduced. Interrow spacing of 90 cm had the greatest SFY (p < .01) for both irrigated and rainfed treatments. The lowest average SFY values were among spacings from 150 to 180 cm, which are most frequently used in the largest-producing countries, depending on the climate zone and water regime. Despite the increase in yield, the use of narrower interrow spacing is limited mainly due to the soil compaction and sugarcane stool damage caused by the currently used tillage and harvesting machines.

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