Effects of Lime and Calcium on Root Development and Nodulation of Clovers

ule formulation are similar to those of secondary root formation (Gresshoff, 1993). Improvements in image Acidic soils can reduce the nodulation of forage legumes. Studies analysis technology allow researchers to assess the efwith a Gilpin series silt loam (fine loamy, mixed mesic, Typic Hapludult) from New, WV, were conducted to determine the effects of lime fects of soil conditions on specific root types, rather on root development, and to assess effects of soil Ca and pH on than just total root length or growth. Recent results innodulation. Liming increased soil pH from 4.8 to 5.3, nodulation, and dicate that different root types respond to environmenroot growth of white clover (Trifolium repens L., cultivar Huia) 28 d tal conditions differently (Zobel, 1992). after planting. Seedlings from unlimed soil formed fewer indetermiIt is still not clear whether the effects of liming on nate and determinate roots. Next, soils were amended with either nodulation are due to changes in soil pH, soil Al, or CaCO3 or a mixture of CaCO3 and CaSO4 to achieve a soil pH of 4.7 soil Ca. In mineral soils, plant available Al is most often to 6.1 and soil Ca of 170 to 680 mg kg 1 soil. There was a strong controlled by soil pH (Thomas and Hargrove, 1984). quadratic relationship between number of nodules per white clover Therefore the effects of soil pH may be due to changes seedling 28 d after planting and soil pH. Another experiment was conducted to determine if these trends were expressed under field in plant available Al. At this time there is no adequate conditions. In 1993, field plots were amended with lime or a coal way of varying soil pH and plant available Al indepencombustion by-product that supplied Ca as CaSO4 and seeded in 1994 dently with the Gilpin series soils. Experiments examinto cool-season grasses. In spring of 1998, plots were drilled with either ing the effects of pH and Al on root growth have been red (Trifolium pratense, L.) or white clover. The nodules per primary conducted using non-soil rooting media (Brauer, 1998, root were determined in May (1998, 1999) and August (1998). Number and references therein). of nodules per primary root was more closely associated with soil pH A series of papers (Lynd and Ansman, 1989a, b; Purthan soil Ca. These results indicate that changes in nodulation were cino and Lynd, 1986) examined the effects of changes more closely associated with changes in soil pH than soil Ca. in soil pH and Ca on nodulation of several legume species. There was no significant increase in nodulation with Ca additions to a soil with an initial pH of 6.1. I is well known that addition of lime to soils will These results may have little bearing on the role of Ca increase the nodulation and growth of legumes (Alin remediating the effects of acidic soil since the soil brecht, 1932, 1933; Hyland, 1938). Increases in soil Ca pH was relatively high in the unamended soil. Alva et may increase nodulation on the basis of the current al. (1987, 1990, 1991) attempted to separate effects of understanding of the role of Ca in nodulation process. Ca, Al, and pH on nodulation. The effects of varying Calcium concentrations in excess of 2 M were necesconcentrations of Al and Ca on nodulation at several sary for optimum growth of Rhizobium in nutrient medifferent pH values were assessed for legumes growing dia (Balatti et al., 1991). Relatively high concentrations in nutrient solution. Their work shows that increases in of Ca, i.e., 10 mM, were necessary for maximal attachmonomeric species of Al were more closely associated ment of Rhizobium meliloti to alfalfa roots in nutrient with decreases in growth and N content than other pasolution (Howieson et al., 1993). Expression of nodularameters. Nodulation in these experiments was relation genes in Rhizobium leguminosarum biovar trifolii tively low, even at higher pH and Ca concentrations in increased with the addition of Ca to the media, espethe absence of Al, perhaps because the nutrient solucially at lower pH values and in the presence of external tions contained inorganic N. Therefore, it is difficult to Al (Richardson et al., 1988). One nodulation protein, conclude that the effects of pH and Al on growth and NodO, appears to be a Ca binding protein (Sutton et N content were due to either reduced nodulation or al., 1994), which suggests that Ca is a regulator of the N uptake. nodulation process. Nodulation factors increase intraPeanut (Arachis hypogaea L.) was grown in a highly cellular Ca levels in root hair cells and alter the fluxes weathered Typic Paleudult soil amended with lime of Ca across the plasma membrane of root hair cells (CaCO3), gypsum (CaSO4), or varying ratios of each (Felle et al., 1998, 1999). Changes in the cytoskeleton (Syed-Omar et al. 1990). Nodulation was greatest when of root hairs in response to Rhizobium attachment inCa was added as gypsum, possibly indicating that changes volve Ca binding proteins (Miller et al., 1997), and thus in soil Ca were mainly responsible for the observed attachment could be influenced by Ca status of roots. effects. The soils used in this experiment were leached Changes in root physiology and structure early in nodule with water after amending, and the addition of Ca as development also involve Ca. These early events in nodeither gypsum or lime resulted in significant decreases in soil Al. The effects of the addition of lime or gypsum David Brauer, USDA/ARS/SPA, Dale Bumpers Small Farms Remay have been due to a reduction in soil Al and/or an search Center, 6883 South State Highway 23, Booneville, AR 72927; Dale Ritchey, and David Belesky, USDA/ARS/NAA, Appalachian increase in soil pH, rather than an increase in soil Ca. Farming Systems Research Center, 1224 Airport Road, Beaver, WV Understanding whether the benefits of lime on the 25813; *Corresponding author ([email protected]). growth and nodulation of legumes are due to effects on soil pH or Ca is of more of concern today than in the Published in Crop Sci. 42:1640–1646 (2002).