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The macaw palm has been domesticated due to its potential use in the production of biofuel, in addition to several co-products that can be generated from its oil and pulp. One of the current challenges in this area is the harvesting, as there are no specific machines for this operation. Therefore, it is necessary to determine the appropriate information regarding the physical properties of the plant, so that it is feasible to develop the technologies necessary for the commercial scale application of macaw palm, allowing it to contribute to the sustainable production of raw material for the biofuel industry and other co-products. The principle of mechanical vibration can be used to shed fruit from trees when ripe, and it can be a method used for harvesting. Thus, as proposed in this study, it was necessary to study the dynamic behavior of the fruit-rachilla system during vibration. Hence, the modal properties of the system were determined. A study on the dynamic behaviors was carried out using a deterministic finite element model, and the natural frequencies were obtained through a frequency-scanning test to evaluate the model. The mean relative error (MRE) between the measured and simulated natural frequencies was also used to evaluate the model. The natural frequencies, determined experimentally, varied from 26.21 to 33.45 Hz on average, whereas the simulated frequencies varied from 24.81 to 39.27 Hz. The overall MRE was 9.08%. Once the model was validated, a sensibility test was carried out, which showed that the density of fruit and the elasticity modulus are the parameters that most influence the natural frequencies of the fruit-rachilla system. [ABSTRACT FROM AUTHOR]

Nitrogen (N) plays a key role in the optimization between corn grain yield and its economic return. Based on that, this study aimed to evaluate the technical feasibility of a portable chlorophyll meter for recommending an economic dose of N under variable rate using different threshold values of the nitrogen sufficiency index (NSI). The study was conducted in Januária-MG (15° 28′ 55″ S, 44° 22′ 41″ W; 474 m) from February to June 2018. The experimental design was a randomized block with 5 treatments and 5 replicates, which were: T0: without N application; T1: 112 kg ha−1 of N (pre-fixed doses), with 50% (56.00 kg) applied in the four expanded leaves stage (V4) and 50% in the V8 stage; T2: 44.8 kg ha−1 of N in V4 + 22.4 kg ha−1 of N through variable rate based on NSI (< 95%) in the stages V8, V10 and V14; T3: 44.8 kg ha−1 of N in V4 + 22.4 kg ha−1 of N through variable rate based on NSI (< 98, 95 and 93%) in the same stages; and T4: 33.6 kg ha−1 of N in V4 + 33.6, 28.0 and 16.8 kg ha−1 of N according to NSI (< 98, 95 e 93%) in V8, V10 and V14, respectively. Variable rate treatments were more efficient than the pre-fixed dose, as they consumed less N and resulted in the same grain yield. Furthermore, the NSI threshold of 95% resulted in higher N use efficiency in the evaluated stages. [ABSTRACT FROM AUTHOR]

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