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Biological nitrogen fixation is a process that occurs in nature and is the cheapest source of N for humid tropical acid soils. The aim of this study was to quantify the amount of N fixed by species of fabaceae through 15N isotopic techniques, in a savanna soil in Mexico. The treatments were established under a design of a randomized complete block, with four replicates. The variables evaluated were: fresh biomass (FB), dry matter (DM), nodule number (NN), nodule dry mass (NDM), total nitrogen (tN) and biologically fixed nitrogen (fN). Our results show that Mucuna deerengiana L. had higher production of FB and DM (17.50 and 5.47 Mg ha-1), NDM (58.79 mg plant-1) and higher content of tN and fN (526.94 and 522.11 kg ha-1) respectively, compared with Cajanus cajan L., Phaseolus lunatus L. and Sesbania emerus L., species that showed low values in these variables. We conclude that Mucuna deerengiana L. tolerates unfavorable factors prevailing in acid soils and therefore has efficiency greater than 500 kg ha-1 fN; we consider it appropriate to increase the level of nitrogen in savanna soils, without applying chemical fertilizers. [ABSTRACT FROM AUTHOR]

To develop an artificial seed of sugar cane using sodium alginate and starch, it was possible to bring shoots resistance and protection in addition to a germination of 100 and 84%, respectively. In order to improve the technology of the artificial seed of sugarcane, two experiments were carried out to evaluate different polymer concentrations (sodium alginate and starch) and determine the maximum storage time for the artificial seed, using a completely random design, and a factorial 5x5 completely random design. The study variables were as follows: physical condition, rheological, mechanical test and seedling emergence. The results obtained have allowed to us to conclude that the best physical condition, resistance and seedling emergence, were obtained with 2% (w/v) sodium alginate and 15% (w/v) starch, corroborating that the initially proposed encapsulation is reliable for the artificial seed elaboration. The seed viability at the fifth day of elaboration was the best choice with a seedling emergence of 100% at the 30 days of planting. Therefore, artificial seed can only be stored for five days to ensure a 100% seed germination. [ABSTRACT FROM AUTHOR]