Sward Leaf Area Index, Root Mass and Nodulation in Arachis Pintoi Cv. Belmonte Subjected to Intensities of Grazing.

Sward leaf area index, root mass and nodulation in Arachis pintoi cv. Belmonte subjected to intensities of grazing

 

Defoliation results in quantitative and qualitative modifications in sward leaf area that alter assimilation partitioning (shoot vs root) and interfere with root growth and nodulation. The objective of this experiment was to evaluate the effect of grazing intensity on shoot and root compartments of Arachis pintoi cv. Belmonte. It was carried out in Piracicaba, SP, Brazil, from February to November, 2013. The response variables studied were sward leaf area index (LAI), root (RM) and nodule mass (NM) and nodule number (NN). Treatments corresponded to four sward heights: 5, 10, 15 and 20 cm, and were allocated to the experimental units (200 m² paddocks) according to a randomized complete block design, with four replications. Two samples (0.33 m²) of herbage mass were harvested per paddock at the ground level in February, June, August and October to represent summer, autumn, winter and spring, respectively. These were hand separated into morphological components and the area of leaflets measured using a leaf area integrator (LAI 3100 – LICOR). Root samples were harvested using a 15-cm diameter iron cylinder for a standard depth of 10 cm. These were washed with pressurized water and hand separated into roots and nodules. LAI was larger on swards managed at 20 cm relative to the other sward heights during summer and spring. During autumn, there was no difference between sward heights and during winter smaller values were recorded on swards managed at 15 cm relative to the others which did not differ from each other. Larger values of RM, NM and NN were recorded on swards managed at 5 and 10 cm. However, the NN:RM ratio was stable between sward heights, indicating that the number of nodes is a function of root growth. There was an increase in NM and RM from summer to spring. On the other hand, NN was similar for summer, autumn and spring, with smaller values recorded only during winter. The results suggest a compensation mechanism between root mass/nodulation and LAI as a means of adapting to the contrasting defoliation regimes imposed.