A B S T R A C TThe rainfall is one of the key regulators of biogeochemical processes of a region, and the understanding of its spatial variability and seasonality throughout the year is fundamental to the management of water resources, and agricultural planning of the Brazilian semi-arid region. Seasonal variability was evaluated from the rain in the Brazilian semi-arid region under three conditions: i) the monthly average of the time series, ii) wettest year (2009) and the driest year (2012). Daily rainfall data was obtained from the database of the National Water Agency (ANA) and were calculated monthly and annual total rainfall, the relative entropy (Dk), the index of seasonality (Sk), the characteristic time of rain (Ck) and the duration of the rainy season (Zk). These variables were spaced to semi-arid region so to enable the interpretation of spatial variability from geostatistics techniques. The magnitude of the coefficient of variation of the variables was similar to the average of the time series, the wettest year and driest year, except for the Ck and the Zk in the driest year. The spherical model of semivariogram was the one of the best represented the spatial variability of most of the variables studied. In the central part of the semiarid, even in the rainiest year, there were the smallest annual values of rainfall. The statistical measures of seasonality and interannual variability of the rainfall used in this study showed a satisfactory performance in the characterization of the behavior of rains in the semi-arid region of Brazil.

The cultivation of adapted species (e.g., forage cactus, sorghum, millet, etc.) can provide greater forage productivity in arid and semi-arid environments. However, due to water limitations in the region, it is important to use irrigation, when well managed, it allows for greater production and provides opportunities for the insertion of intercropping crops even in dry periods. Thus, this review aimed to survey the main indices of biological efficiency, competitive ability and economic benefit in different forage species and crops, as well as the use of resilient practices that seek to increase the efficiency and sustainability of forage production in an environment semi-arid. Scientific articles in Portuguese and English from the last ten years were used, using the following platforms: Google Academic, Scielo, ScienceDirect, Scopus, and Web of Science, paying attention to the quality and timeliness of the literature cited. The use of resilient agricultural practices such as irrigation, planting of adapted species, straw mulch and intercropping are of great importance for productive units in the Brazilian semi-arid region. As well as the use of indices of biological efficiency, competitive ability and economic return, which are capable of helping to determine the best configurations of intercropping crops, providing greater reliability and profitability of the agricultural chain in semi-arid regions.

A fertilização química por um longo período pode acarretar em vários efeitos negativos para o solo e consequentemente para o desenvolvimento das culturas, por isso é importante buscar formas alternativas de fertilização que proporcione a preservação do ambiente de cultivo e um crescimento vegetal eficiente e sustentável. A inoculação de plantas com bactérias fixadoras de nitrogênio tem mostrado resultados bastante positivos em vários trabalhos científicos com diversas espécies vegetais de interesse econômico. Além disso, é uma fonte de nitrogênio mais barata que o fertilizante nitrogenado, diminuindo custos com mão de obra e uso de maquinário. Entretanto as bactérias de inoculantes comerciais podem ter sensibilidade aos estresses abióticos do local a serem introduzidas, diminuindo a eficiência do produto, principalmente em regiões de clima semiárido devido às altas temperaturas do ar, longos períodos de secas e problemas com salinidade do solo e da água. O uso de estirpes nativas pode apresentar maior eficiência de fixação de nitrogênio e desenvolvimento das plantas em condições adversas, por serem adaptados a essas condições. Estudos em ambientes semiáridos mostraram que essas estirpes possuem eficiência de aquisição de nitrogênio igual ou superior ao uso de inoculantes comerciais ou adubação nitrogenada. A utilização de inoculantes voltados para estirpes adaptadas às condições semiáridas pode promover o desenvolvimento da agricultura local, devido à diminuição com a adubação nitrogenada e possibilidade de inserção de outras culturas no sistema de produção. Entretanto, o processo de formulação de um novo inoculante para o mercado demanda recursos, pesquisas e demora anos para ser concluído.

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