Do different densities and planting orientations of forage cactus alter agronomic, morphophysiological characteristics, and soil water dynamics in a semiarid region?

Water scarcity is a problem that affects agricultural production around the world. Increasing forage production in the semiarid region is necessary to maintain animal production, and consequently food security. Different agronomic management can improve growth and productivity responses and the water-economic indexes of the crop. Therefore, this study aimed to evaluate how the management of density and orientation of forage cactus plantations modify the morphophysiological indices, phenophases, cutting moment, productivity, soil water balance, and water-economic indicators in a semiarid environment. The study was carried out during two harvests (2020–2021 and 2021–2022) in the Brazilian semiarid region. Three experiments were conducted with the ‘Orelha de Elefante Mexicana’ clone under a randomized block design and four replications. Two experiments were composed of five planting densities (100,000, 50,000, 33,000, 25,000, and 20,000 plants ha−1) modified by the spacing between plants (0.10, 0.20, 0.30, 0.40, and 0.50 m with a fixed distance of 1.00 m between rows), the first with East-West (EW) orientation and the second with North-South (NS) orientation. The third experiment presented four planting densities (50,000, 40,000, 33,000, and 28,571 plants ha−1) modified by the distance between rows (1.00, 1.25, 1.50, and 1.75 m with a fixed distance of 0.20 m between plants). Biometric and biomass data were used to determine morphophysiological indices, delimitation of phenophases, ideal cutting moment, and fresh matter (FM) and dry matter (DM) productivity. The soil water balance was carried out using soil moisture readings and the physical-water properties, and the crop's water-economic indices were calculated. In general, morphophysiological indices, phenophases, and cutting moments were affected by densities (p<0.05). DM productivity was 16 % higher in the EW orientation (27.7 Mg ha−1) compared to the NS orientation. The highest planting density (100,000 plants ha−1) in the 1.00 × 0.10 m arrangement presented the highest averages of FM and DM of the cycles, being 401.5 and 32.4 Mg ha−1 orientation EW and 420.8 and 29.5 Mg ha−1 orientation NS. Density of 50,000 plants ha−1 in the 1.00 × 0.20 m arrangement (265.5 and 23.5 Mg ha−1 of FM and DM, respectively). This same behavior occurred for water and economic indices. Therefore, higher densities in forage cactus cultivation (100,000 plants ha−1 in the East-West planting orientation and 50,000 plants ha−1) must be adopted to enhance forage production in semiarid regions.