Sistemas de cultivo da palma forrageira irrigada no semiárido potiguar

Abstract

Cactus pear is strategically important as food support for livestock in the semiarid region of Brazil, however, some localities do not have adequate climate for its full development, requiring hydric complementation. Two experiments were conducted from 2017 to 2019 in Apodi - RN- Brazil. In the first trial the objective was to evaluate the effects of salinity levels of irrigation water (0.1, 2.5, 5.0, 7.5 and 10 dS m-1) and the presence or absence of soil cover with rice husk on morphophysiology and productivity of spineless forage cactus IPA Sertânia (Nopalea cochenillifera) in two annual cycles. The treatments were randomized in strip plot scheme, in a randomized block design. Salinity levels were applied in the plots, and the soil cover in the subplots with four replicates. The average drip irrigation depth was 4.0 mm week-1. The interaction between salinity levels and years was significant (P <0.05) for fresh matter (FMP) and dry matter (DMP) productivity, water use efficiency (WUE) and cladode thickness characteristics, with negative responses to higher salinity levels only in the first year and absence of effects in the second year (117 and 7 Mg ha-1 year-1 of FMP and DMP, respectively). The soil cover promoted higher FMP (96 Mg ha-1 year-1), number of cladodes per plant (10 units), thickness (2.1 cm) and cladode area (323 cm2) and lower DM content (78 g kg-1). The years of evaluation influenced significantly, so the second annual crop cycle benefited the formation of larger plants and cladodes. Rice husk cover promoted an increase in sprouting and FMP, and salinity at the highest levels (7.5 and 10.0 dS m-1) contributed to lower DMP of IPA Sertânia cactus variety in the first annual cycle, but without significant differences between the levels of water salinity at the next harvest. In the second experimental trial, the objective was to verify the morphological and productive responses of spineless forage cacti cultivars – Orelha de Elefante Mexicana (OEM) (Opuntia stricta), Miúda (Nopalea cochenillifera Salm Dick) and IPA Sertânia (Nopalea cochenillifera) under different planting densities (20 , 40 and 80 thousand plants ha-1) and irrigation hours (morning and evening), in two annual harvests. The treatments were randomized in sub-subdivided plots, in a completely randomized design. The irrigation hours represented the plots, the cacti cultivars the subplots, and the planting densities the sub-subplots, with four replicates. The applied water depth was 15 mm week-1 via sprinkler system. Regarding the morphological characteristics, the OEM and the IPA Sertânia cultivars presented larger cladodes dimensions, while the Miúda cultivar showed higher plants. The higher density favored the increase of cladode area index (6.0 m2 /m2). Regarding the productive responses, in the first year of growth, there was a significant interaction (P <0.05) between irrigation hours and planting densities for fresh matter productivity (FMP), with the daytime and the density of 80 thousand plants ha-1 promoting higher yield (197 Mg ha-1 year-1). There was a significant interaction effect between cultivars and planting densities for cladode number, FMP, dry matter productivity (DMP) and water use efficiency (WUE), especially for Miúda and OEM cultivars. The Miúda cultivar emitted 53 cladodes/plant under 20,000 plants ha-1 and FMP, DMP and WUE of 212 Mg ha-1 year-1 and 23 Mg ha-1 year-1 and 19 kg of DM kg of water-1, respectively, under the higher density. Opuntia (OEM) reached 217 and 22 Mg ha-1 year-1 and 19 kg of DM kg of water-1 for FMP, DMP and WUE, in this order, under the lowest planting density. In the second annual growth cycle, the irrigation hours had a significant effect (P <0.05), so that the daytime allowed higher FMP (197 Mg ha-1 year-1), DMP (17 Mg ha-1 year-1) and WUE (12 kg of MS kg of water-1). The effect of the cultivars was significant (P <0.05) for DMP and WUE, with evidence for the Miúda cultivar. Spineless forage cactus cultivars were influenced by irrigation hours and planting densities, especially Miúda and OEM, both with high productive potential.