Seeding Rates of Ball Clover in Mixtures with Annual Ryegrass in North Florida

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1 Seeding Rates of Ball Clover in Mixtures with Annual Ryegrass in North Florida E.R.S. Santos 1, H.M.S. Silva 1, M. Ruiz-Moreno 1, A. Blount 1, C. Mackowiak 1, N. DiLorenzo, L. E. Sollenberger 2, J.C.B. Dubeux Jr 1 Synopsis Legumes have the capacity to associate with rhizobia strains and fix atmospheric N 2. Ball clover has reseeding ability and when planted in mixtures with annual ryegrass contributes by adding N to the system and extending the grazing season. Summary Legumes have the capacity to associate with rhizobia strains and fix atmospheric N 2. Ball clover has reseeding ability and when planted in mixtures with annual ryegrass contributes by adding N to the system and extending the grazing season. This experiment tested three seeding rates of ball clover (2, 4 and 6 lb/acre) in a mixture with annual ryegrass compared with annual ryegrass in monoculture, fertilized (45 lb N/acre), or not fertilized with N. Response variables included percentage of ball clover, dry matter yield (DMY) of annual ryegrass, DMY of ball clover, total DMY, percentage of plant N derived from atmosphere (%Ndfa) and N fixed contained in the shoot (Nfix). The study was performed in a randomized complete block design with 4 replicates. Ball clover proportion in the mixture increased from 32% (at 2 lb/acre seeding rate) to 47% (at 4 lb/acre seeding rate), with no difference observed between 4 and 6 lb/acre. Ball clover DMY increased linearly with increasing seeding rates, with DMY of 630, 910, and 1040 lb/acre for 2, 4, and 6 lb/acre seeding rates, respectively. Annual ryegrass DMY and total DMY were greater in the N fertilized treatment (3,400 lb DM/acre). Average %Ndfa was 95% for ball clover and there was no difference among treatments. The Nfix showed a linear increase with seeding rate (P=0.02) with values ranging from 16 to 25 lb N/acre. Treatments including seed rates of 4 and 6 lb/acre were similar in botanical composition, DMY of ball clover, DMY of ryegrass, total DMY, and Nfix. From the producer perspective, it is more economical to use 4 lb of ball clover seed/acre. Increasing seeding rates of ball clover in annual ryegrass mixtures allowed greater legume contribution in the pasture, improving forage N without decreasing yield. Introduction Clovers have the ability to naturally reseed because of seed dormancy during the warm-season. Proportion of hard seeds is an important trait driving natural reseeding. Reseeding ability also depends on grazing management. During flowering and seed maturation, it is important to manage livestock to allow plants to set seeds and let seeds mature before they are consumed by livestock. Mature seed consumed by livestock will likely pass through the gastrointestinal tract and return to the soil via feces. Hard seeds usually are not digested in the rumen and they have the ability to germinate when returned to the soil, after the dormancy period has passed. Seeds not ingested by grazing animals return directly to the soil. 1 University of Florida/IFAS North Florida Research and Education Center, 3925 Highway 71, Marianna, FL. 2 University of Florida/IFAS Agronomy Department, Gainesville, FL.

2 Once again, the proportion of hard seeds and seed dormancy will define the ability of these seeds to germinate in the following cool-season. Ball clover (Trifolium nigrescens Viv.) has reseeding ability and when planted in mixtures with annual ryegrass contributes to add N to the system and to expand the grazing season. Seeding rates of ball clover for optimum growth of both forages in mixtures need to be investigated. Therefore, the overall objective of this experiment was to test three seeding rates of ball clover (2, 4, and 6 lb/acre in a mixture with annual ryegrass compared with annual ryegrass in monoculture, fertilized with 45 lb N/acre or not fertilized. Material and Methods The experiment was conducted at the North Florida Research and Education Center, Marianna, FL. In order to establish the trial, soil samples were collected and the plots fertilized according to UF/IFAS Standardized Fertilization Recommendations for Agronomic Crops (Mylavarapu, 1997). Treatments were three seeding rates (2, 4, and 6 lb/acre) of ball clover in a mixture with annual ryegrass compared with annual ryegrass in monoculture, fertilized with 45 lb N/acre or not fertilized. Seeding rate for annual ryegrass was 20 lb/acre. Nitrogen fertilizer was applied on March 3, 2015, using urea as a source of N. Plots measured 6 x 20 ft and were established in a randomized complete block design (Figure 1) with 4 replicates (n=20). Samples were taken on April 4, 2014, by harvesting two 2.7 sq. ft. quadrats per plot to a 2-inch stubble height. Samples were dried at 131 F for 72 h after sampling. Response variables included percentage of ball clover, total dry matter yield (DMY), clover DMY, shoot N mass, botanical composition, percentage of N derived from atmosphere (%Ndfa) and N fixed contained in the shoot (N fix ). The proportion of nitrogen derived from atmosphere was determined by using the equation described by Unkovich et al. (2008). Data were analyzed by using the Proc Mixed from SAS and means were compared using PDIFF adjusted by Tukey (P<0.05). Treatments were considered to be fixed effects and random effects included blocks and its interactions with fixed effects. Results Seeding rates of 4 and 6 lb/ac had greater clover contribution to total DMY (P=0.03). For these seeding rates, ball clover represented, respectively, 47 (1,000 lb/acre) and 46% (1,040 lb/acre) of the total dry weight, while at the rate of 2 lb/acre ball clover contributed only 32% of total DMY. There was no difference in the percentage of N derived from the atmosphere (%Ndfa) among clover treatments. The %Ndfa was 95, 97, and 94 for 2, 4, and 6 lb/acre, respectively. Nitrogen harvested in the shoot was 50% greater when seeding rate increased from 2 to 4 lb/acre, but no differences were observed between 4 and 6 lb/acre. Despite the contribution of clovers to the total DMY, annual ryegrass showed a greater yield (3,400 lb DM/acre) when fertilized with 45 lb N (P=0.0007), and there was no significant difference among treatments containing clovers (1,950, 2,030, 2,190 lb DM/acre for 2, 4, and 6 lb/acre, respectively) and the unfertilized ryegrass (1,620 lb DM/acre). In a grazing system, however, forage quality must be taken into account. Legumes generally have greater crude protein and digestibility than grasses, especially the cool-season legumes. Greater nutritive value might lead to better animal response. Shoot N yield in annual ryegrass was also greatest for the fertilized treatment (P<0.0001), and there was no difference among the treatments with clovers or the unfertilized annual ryegrass. However, no difference in total N yield was detected between the treatments containing clovers and the fertilized

3 ryegrass (28, 37, 46, 49 lb N/acre for the rates of 2, 4, 6 lb/acre, and the fertilized annual ryegrass, respectively), and they all differed (P=0.002) from the unfertilized annual ryegrass (15 lb/acre). Conclusions Total dry matter yield was not different among the different seeding rates of ball clover in mixture with annual ryegrass and the unfertilized annual ryegrass monoculture. Ball clover-annual ryegrass mixtures also yielded less compared with N-fertilized annual ryegrass. Clover contribution, however, has potential to improve animal performance and reduce off-farm N inputs via mineral fertilization. Because there were no significant differences in any variable between the seeding rates of 4 and 6 lb/acre, from the producer s perspective it is more economical to adopt the seeding rate of 4 lb/acre if considering planting the ball clover-annual ryegrass mixture. Literature Cited Mylavarapu, R., Wright, D., Kidder, G. UF/IFAS Standardized Fertilization Recommendations for Agronomic Crops. UF/IFAS extension, SAS Institute SAS Inst., Cary, NC. Sollenberger, L.E In Proc. Brazilian Soc. Animal Sci. Mtg., 51st, Barra dos Coqueiros, Brazil. 29 July-1 Aug Sociedade Brasileira de Zootecnica, Brasilia, Brazil.

4 Figure 1. Ball clover seeding rate trial at UF/IFAS NFREC, Marianna, FL. Table 1. Ball clover %, total clover dry matter yield (DMY), nitrogen derived from atmosphere and nitrogen fixed, in mixtures of ball clover-annual ryegrass under different seeding rates of ball clover. Treatments Ball Clover, % Clover DMY, lb DM/acre Ndfa 1, % Nfix 2, lb/acre 2 lb/acre 32 b 634 b 95 a 16 b 4 lb/acre 47 a 996 a 97 a 24 a 6 lb/acre 46 a 1,039 a 94 a 25 a SE P Ndfa is N derived from atmosphere 2 Nfix is N fixed contained in the shoot a,b Means in a column with different superscripts differ P<0.05

5 Table 2. Total dry matter yield (DMY), total shoot nitrogen mass, total nitrogen yield, and ryegrass percentage under different seeding rates of ball clover, in contrast with unfertilized annual ryegrass and fertilized annual ryegrass (45 lb N/acre). Total DMY, Shoot N yield Total N Yield Ryegrass, Treatments lb DM/acre Ryegrass, lb/acre lb/acre % 2 lb/acre 1,954 b 16 b 28 a 65 b 4 lb/acre 2,034 b 12 b 37 a 50 b 6 lb/acre 2,186 b 18 b 45 a 50 b Fertilized Ryegrass 3,399 a 49 a 49 a 97 a Unfertilized Ryegrass 1,624 b 15 b 15 b 96 a SE P < < a,b Means in a column with different superscripts differ P<0.05.