John Caddel, Hailin Zhang, and Kendra Wise
Plant and Soil Sciences Department
Oklahoma State University

Forage legume are important for livestock production as components of pastures and in pure stands. Forage yield and quality of legume crops are generally negatively affected by soil acidity. This study was conducted to determine the effect of lime applications, 0.4, 0.7, 1.2, 2.0, and 3.7 tons effective calcium carbonate equivalent (ECCE)/acre, on soil pH, alfalfa (Medicago sativa L.), red clover (Trifolium pratense L.), and white clover (T. repens L.).

Soil pH: The legume species were planted in separate subplots within each lime treatment. Soil samples, collected and analyzed twice a year for three years, showed lime increased soil pH for 14 months, and then pH slowly declined (Figure 1).

Stand Establishment: Lime application did not affect legume seedling density, but suppressed certain weed populations, as measured by number of plants per ft² (Table 1 and 2). More seedlings of certain weeds were observed at low pH levels during establishment, but their numbers were low enough to not create problems for legume germination and development. Rattail fescue was the predominate weed at this site, and it was most prevalent in areas of low pH. The population of rattail fescue decreased as pH increased (Table 2). This weed could be used as an indicator weed, which could aid producers in identifying areas of low pH.

Forage Yield: Red clover and alfalfa had a significant increase in yields with increasing pH, but white clover did not respond to lime with an increase in yields above a pH of 5.2. Alfalfa and red clover forage yields were adversely affected by low soil pH although reactive Aluminum concentration was low. Alfalfa and red clover responded positively to pH increase caused by lime treatments; however, white clover yields did not increase significantly above a pH of about 5.2. (Fig. 2-4)

Stand Persistence: The variable pH did not affect the number of alfalfa and red clover plants present after 3.5 years, as measured by number of plants per ft²., but higher pH resulted in larger plants. Alfalfa plants that grew in the high lime treatments were as much as 69% larger than those in low pH treatments (Table 3).

Forage Quality: Protein concentration in the forage was not affected by lime treatments.

Importance: This information can be useful in finding economically sound liming practice for soils with low Al saturation and Mn concentration. The Oklahoma Cooperative Extension Service recommends lime for legume production when soil pH is below 6.1, but this study showed white clover did not benefit from liming above a 5.2 pH, when all other nutrient needs were satisfied and Al saturation and Mn concentration was low. On the other hand, alfalfa yields were highest at pH levels about 7, strongly suggesting the need for different liming recommendations for different forage legumes.

Figure 1. Soil pH changes over time for five lime treatments (tons ECCE/acre). Lime was applied in April 2000, and samples were collected before lime was applied and 7, 14, 18, 24, 30, 35, and 43 months after lime was applied near Haskell, OK. 2000-2003.

Figure 2 Relationship between annual mean alfalfa forage yield (tons/acre) and pH for 2001, 2002, and 2003, Haskell, OK. Soil pH is the mean of spring and fall pH measurements.

Figure 3. Relationship between annual mean red clover forage yields (tons/acre) and pH for 2001 and 2002, Haskell, OK. Soil pH is the mean of spring and fall pH measurements.

Figure 4. Relationship between annual mean white clover forage yields (tons/acre) and pH for 2001 and 2002, Haskell, OK. Soil pH is the mean of spring and fall pH measurements.

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