RESUMO Este estudo teve como objetivo verificar os efeitos do fósforo sobre a fotossíntese e o crescimento de

Integrated crop-livestock systems in regions with dry winters could be a viable option to increase food production during periods of irregular rain and reduced pasture availability. A corn (Zea mays L.) silage production system with cover crops of (a) the weedy growth of signal grass [Urochloa decumbens (Stapf) R. Webster "Basilisk"] and (b) palisade grass [Urochloa brizantha (Hochst. ex A. Rich.) R. Webster 'Marandu' and 'Piatã'], both with a 0.20-and 0.45-m silage cutting height, was employed in the summer and autumn. Yellow oat (Avena byzantina cv. São Carlos) was oversown in these systems in the winter and spring. The pasture production, the daily ration intake, the performance and carcass characteristics of lambs (Ovis aries) grazing these pastures in a semi-feedlot system (supplemented with silage and concentrate), and the revenue were investigated. The experiment was repeated in the same location for two growing seasons (2010-2011 and 2011-2012) on a Typic Haplorthox in Botucatu, São Paulo, Brazil. Analyzing the system as a whole, intercropping corn silage with palisade grass cv. Marandu (followed by palisade grass cv. Piatã) with a cutting height of 0.45 m combined with yellow oat oversowing was the most robust option for enhancing productivity. The pasture formation for lamb finishing in a semi-feedlot system, the reduction of silage and concentrate intake, and greater live weight and carcass gains per hectare were key attributes for improving the economic viability of this integrated crop-livestock system. Thus, these crop systems were a viable option for the diversification of agricultural activities in tropical regions.

Overseeding warm‐season legumes into warm‐season perennial grass pastures may increase productivity and nutritive value of pastures in tropical and subtropical regions. The objective of this study was to investigate the effects of overseeding ‘Amarillo’ pintoi peanut (Arachis pintoi Krapov. & W.C. Greg.) into Jiggs bermudagrass [Cynodon dactylon (L.) Pers.] pastures grazed at different stubble heights. The experiment was conducted in Ona, FL, from June to October in 2014 and 2015. Treatments were a split‐plot design of two sward types (bermudagrass monocultures or overseeded with pintoi peanut, main plots) and two postgrazing stubble heights (15 or 25 cm [SH15 and SH25], subplots) arranged in a randomized complete block design with four replicates. Pastures were mob stocked, with 28‐d resting periods between grazing events. There was no effect of stubble height on pintoi peanut plant density (5.8 plants m−2), ground cover (5.8%), or proportion in the herbage mass (HM, 5.2%); however, proportion in the HM increased from 1.1 to 8.2% over 2 yr. There was no effect of sward type on weed ground cover; however, SH25 had greater weed ground cover than SH15 (53.4 vs. 18.2%). Herbage accumulation rate, crude protein, and in vitro digestible organic matter were not affected by sward type (23.4 kg ha−1 d−1, 101 g kg−1, and 431 g kg−1, respectively). Pintoi peanut proportion in the HM increased over time; however, it may take >2 yr to have a significant presence of pintoi peanut in the mixed sward.

Rhizoma peanut (Arachis glabrata Benth.) is a widely used warm‐season legume in Florida. Ecoturf is a rhizoma peanut germplasm with superior nutritive value; however, there is limited information about the effects of regrowth interval on this characteristic. The objective was to investigate the effects of regrowth interval on in situ crude protein (CP) and dry matter (DM) disappearance of Ecoturf compared with the predominant cultivar ‘Florigraze’. The experiment was conducted from July to October of 2014 and 2015. Treatments were a split‐plot design of Florigraze and Ecoturf (main plots) harvested at regrowth intervals of 4, 8, and 12 wk (subplots), distributed in a randomized complete block design with four replicates. Samples of each treatment were incubated in two steers (Bos spp.) for 0, 3, 6, 9, 12, 24, 48, and 72 h, and DM and CP disappearance were fit to a nonlinear model. Ecoturf had greater CP concentration than Florigraze (193 vs. 168 g kg−1). There was no effect of genotype on in situ effective disappearance of CP (715 g CP kg−1); however, there was a quadratic effect of regrowth interval. Ecoturf had greater effective disappearance of DM than Florigraze only at 4 wk of regrowth (597 vs. 563 g kg−1). Dry matter and CP disappearance parameters may differ between Ecoturf and Florigraze. Harvesting at a regrowth interval of 8 wk or less may improve rhizoma peanut nutritive value.

Water deficiency during the dry seasons influences the relationship between water and gas exchange in tropical grasses, reducing their productive potential. In addition, the phosphorus (P) deficiency Brazilian soils adds to the set of factors limiting crop production. In this context, the objective of this study was to evaluate the responses of different tropical forage species to phosphorus supplementation as mitigating the damage caused by water stress. Seeds of Urochloa brizantha cv. MG-4, Urochloa decumbens cv. Basilisk, Panicum maximum cv. Áries, Panicum maximum cv. Tanzânia and Paspalum atratum cv. Pojuca were germinated in pots containing 10 liters of red-yellow Acrisol type soil. Experiments were conducted by combining levels of phosphorus, 8,0 and 100,0 mg of P dm-3, with two irrigation regimes, 100 and 40% replacement of transpired water. The biometric parameters, photosynthetic capacity, leaf water potential and soil chemical characteristics were evaluated, and the data was submitted to analysis of variance (ANOVA, p < 0.05), and subsequently the means were compared using a Tukey test (p < 0.05). The results showed for tropical grasses grown under water stress, there is a clear mitigating effect of phosphorus supplementation, especially on the maintenance of biomass growth.