Warm-Season Grass-Legume Mixtures Options for North Florida

Transcription

1 Warm-Season Grass-Legume Mixtures Options for North Florida E. Santos 1, J. Dubeux 1, C. Mackowiak 1, A. Blount 1, D. Jaramillo 1, L. Garcia 1, J. Shirley 1, B. Conrad 1, M. Ruiz-Moreno 1 Synopsis Nitrogen fertilization has a great impact on grass yield, however, N application may be costly for producers and may cause environmental damages. Legumes are capable of fixing atmospheric N. When grasses are growing in mixtures with legumes they can utilize this N, thus we aimed to investigate options for grass-legume mixtures during the warm-season for north Florida. Summary Mixing grasses and legumes may decrease the costs with N fertilization and create a more sustainable system. Two trials were performed on two farms to evaluate grass-legume options for north Florida. The first trial contained bahiagrass and the second trial contained bermudagrass. The treatments for each trial were unfertilized grass, N-fertilized grass, grass-alfalfa, grass-rhizoma peanut, alfalfa, and rhizoma peanut (RP), with the mixtures receiving half of the N applied in the N-fertilized grass. Each treatment was replicated four times in a completely randomized design. A total of seven harvests were made during the growing season to estimate herbage accumulation and botanical composition. In general, mixtures and N-fertilized grass presented similar herbage accumulation, however, legumes did not show a significant contribution throughout the year. Rhizoma peanut was not significant in the botanical composition, the stubble height used may have misrepresented RP contribution. Alfalfa had a greater contribution in the first harvest, and declined along the year, behaving as annual. Grass-legume mixtures may decrease N fertilization, nevertheless it is not clear if the similar herbage accumulation was caused due to the grasses could not respond to greater amounts of N fertilization than they were receiving in the mixtures. Introduction Hay production is one of the most important agricultural activities in North Florida. Bahiagrass, bermudagrass, and perennial peanut are the most planted forages in this area during the warm-season, and alfalfa has been considered an emerging crop in the region. Warm-season perennial grasses usually have high yields when properly managed and fertilized with nitrogen. However, nitrogen losses and market price variability may decrease farmers profitability. In addition, the manufacturing process, transportation, storage, and application of nitrogen add greenhouse gases to the atmosphere, which contribute to global warming. Nitrates can be leached and contaminate the groundwater. High levels of nitrate in drinking water may cause health problems in humans and animals. Forage legumes are capable of naturally fixing atmospheric nitrogen in association with rhizobia bacteria. Once growing together with legumes, grasses can utilize the fixed nitrogen and also stimulate the fixation due to nutrient competition. Mixing grasses and legumes can potentially decrease synthetic nitrogen fertilizer application, decrease production cost, mitigate environmental damages, and create a more sustainable system. This study aims to investigate the performance of grass-legume mixtures as an alternative to reduce industrial N fertilizer application. Material and Methods Two trials were designed to show the contrast between grass-legume mixture and their monocultures, they were replicated on two farms (Farm 1 and Farm 2). One trial contained bermudagrass cv. Tifton 85, as the grass component, while the other trial contained bahiagrass cv. Tifquik. For each trial, treatments are as follows: grass monoculture; grass monoculture + 80 lbs N/ac (after each harvest); perennial peanut (RP) monoculture (Florigraze), alfalfa monoculture (Alfagraze 600 RR), grass + RP + 40 lbs N/ac, and grass + alfalfa + 40 lbs N/ac. All treatments received 300 lbs of after each harvest. Each treatment 1 North Florida Research and Education Center, University of Florida, Marianna, FL

2 was replicated four times in a randomized complete block design. Plots measure 200 ft 2 (10 x 20 ft.) with alleys of 6 ft. between blocks and trials. Irrigation was applied at Farm 2 according to farmer s management. Measurements were taken every 5 wks during the growing season in an area of 5 ft 2 at 3 in. Grass and legume components were hand-separated and dried at 55 C for 72 h in order to obtain the yield and botanical composition. A series of herbicides were used to control weeds (Table 1.). Results Farm 1 Bahiagrass-legume mixtures Results showed that when bahiagrass was growing together with alfalfa or RP and receiving 40 lb N/ac the yield was similar to the N-fertilized bahiagrass (Figure 1A). May, June and August were the months with greater HA. Unfertilized bahiagrass HA was greater or similar than alfalfa and RP monocultures throughout most sampling dates, however, legume monocultures and unfertilized bahiagrass were never greater than any treatment receiving N fertilization. Rhizoma peanut and alfalfa were the least productive forage crops, followed by unfertilized bahiagrass. N-fertilized bahiagrass, bahiagrass-rp, and bahiagrassalfalfa total HA did not differ between each other during sampling dates. The botanical composition was estimated in the mixed treatments, in order to assess the proportion of each component (grass or legume) in the stand. Rhizoma peanut did not have a representative contribution in the botanical composition. One factor that contributed to the non-appearance of RP in the BC was the stubble height used to harvest (7.5 cm) which was probably too high for RP. The mixture of alfalfabahiagrass had a significant proportion of alfalfa in the first harvest (61%), however in decline in the second (8%) and in the third evaluation (0.2%), disappearing completely in the fourth (Figure 2A). Farm 1 Bermudagrass-legume mixtures There was no difference among treatments in HA during the first two harvests. Most of the crops were dormant, only alfalfa was growing, however, it did not yield as much as expected. May was the best month for the DM production. The N-fertilized bermudagrass HA was 4068 lb DM/ac, and it was greater than any other treatment (Figure 1C). Mixtures were intermediate between N-fertilized bermudagrass and the other monocultures, besides all treatment differ among each other in May unfertilized bermudagrass and legumes were similar during most of the evaluations. However, the similarity in the first two months was due to physiological reasons, where bermudagrass and RP were still dormant.). Despite showing greater yield than all the monocultures, N-fertilized bermudagrass yield was only greater than both mixtures in May and September. Rhizoma peanut presence above 7.5 inches was not significant in mixed stands. On the other hand, alfalfa was present in the mixtures, mainly during the first harvests of the year. Therefore, a decline from the first to the last harvest was noticed on both sites. Alfalfa contribution was 50% in April, however, it only represented 10, 5, and 1% in May, June, and August, respectively (Figure 2C). During September and October, there was no alfalfa left in the mixed plots. Farm 2 Bahiagrass-legume mixtures Mixtures of bahiagrass with RP or alfalfa had similar yield when compared to the N-fertilized bahiagrass and they were greater than unfertilized bahiagrass, alfalfa, and RP yield (Figure 1B). However, no difference was noticed in the first and second harvests (March and April) due to environmental conditions which did not favor warm-season legumes growth. May, June, and August were the months with greater forage mass. Unfertilized bahiagrass, RP, and alfalfa were the least productive treatments and did not differ between each other. It is important to mention that overall yield in Farm 2 was greater than in

3 Farm 1. This yield difference was caused by the irrigation used in Farm 2, while Farm 1 relied on rainfall only. Botanical composition (BC) As it happened in the non-irrigated site (Farm1), RP also did not have a representative contribution in the botanical composition. However, alfalfa had an average of 18% in the BC of the mixture of alfalfabahiagrass (Figure 2B), therefore the first and second harvests were the ones to have a greater proportion of alfalfa (34 and 40%, respectively). The contribution of alfalfa in the harvests occurring from May to October ranged from 5 to 17%. Farm 2. Bermudagrass-legume mixtures Herbage Accumulation (HA) The greater difference between treatments was in May when the N-fertilized bermudagrass out yielded all the other treatments (3230 lb DM/ac), followed by bermudagrass-rp and bermudagrass-alfalfa, which yielded 1722 and 1561 lb DM/ac, respectively (Figure 1D). Unfertilized bermudagrass, alfalfa, and RP were less productive than the other treatments. When irrigation was present, alfalfa contribution was 84, 41, 19, 13, 4, and 2%, for April, May, June, August, September, and October (Figure 2D). Despite the better performance under irrigation, at the end of the season, the alfalfa presence in the mixed stands was not significant. Acknowledgements The authors acknowledge the Florida Department of Agriculture & Consumer Services for supporting the study. Table 1. Herbicides applied for controlling weeds. Treatments Strategy Product rate per acre Only Grass GrazonNext HL 1.5 pt Fertilized Grass GrazonNext HL 1.5 pt Grass + Peanut 2, 4 D 1 pt Grass + Alfalfa 2,4 DB pt Alfalfa (RR) Roundup 33 fl. oz Roundup wheathermax 4.5S Perennial Peanut Impose and Clethodim 4 oz and 12 oz, respectively

4 Figure 1. Grass-legume mixtures herbage accumulation in comparison with their monocultures. The N-fertilized grass received 80 lb N/ac/harvest, and the mixtures receive 40 lb N/ac/harvest. A) mixtures with bahiagrass at Farm 1; B) mixtures with bahiagrass at Farm 2; C) mixtures with bermudagrass at Farm 1; D) mixtures with bermudagrass at Farm 2.

5 Figure 2. Grass-alfalfa mixtures botanical composition. A) mixture with bahiagrass at the Farm 1; B) mixture with bahiagrass at Farm 2; C) mixture with bermudagrass at Farm 1; D) mixture with bermudagrass at Farm 2.