Soybean and Soybean Cyst Nematode Response to Soil Water Content in Loam and Clay Soils

Soybean cyst nematode (Heterodera glycines Ichinohe) (SCN) a major pest of soybean [Glycine max (L.) Merr.] in the southeastern USA. The objective of this study was to determine the effect of wet and dry silt loam and clay soils on SCN development and corresponding soybean yield response in a greenhouse study. ’Tracy-M’ soybean was grown in pots that contained either Dubbs ilt loam (fine-silty, mixed, thermic Typic Hapludal0 or Sharkey clay (very fine, montmorillonitic, nonacid, thermic Vertic Haplaquept) surface soils that were watered to maintain adequate soil water potential (SWP) (-30 kPa SWP, wet treatment), or had water added at onehalf the rate of the adequate treatment (dry treatment). Nematode treatments were either infested or noninfested. Experiments were conducted in 1987, 1988, and 1989, and new soil was infested each year. Number of cysts increased significantly with time in the wet silt loam treatment, stayed the same as the initial infestation in the dry silt loam treatment, and declined significantly in both the wet and dry clay treatments in all years of the study. Infestation by SCN caused a reduction in seed yields in both soils, but the decrease was less in the clay soil. Soil water content in each soil interacted with level of SCN infestation to influence soybean yield. The interaction was not dependent on similar SCN infestation levels between soils, or similar differences in SCN infestation between wet and dry soil treatments within soil. Yield declines associated with SCN infestation were highly correlated with number of seed. These results indicate that SCN will not maintain populations in fine-textured clay soil under greenhouse conditions, nor result in the magnitude of yield decline that often is measured in coarse-textured soil. S CYST NEMATODE is injurious to soybean, and infests soils throughout the midand lower Mississippi River Valley and the southeastern coastal plain in the USA (Riggs and Schmitt, 1987). Studies have investigated effects of soil pore space, temperature, moisture, texture or type, and aeration on nematode population levels. These reports indicate that edaphic factors can significantly influence infestation, development, egg hatch, survival, migration, and infectivity of many nematode species. Influence of soil moisture content on nematode development has been observed with Rotylenchulus reniformis Linford & Oliveira (Rebois, 1973), Pratylenchus penetrans (Cobb) Filipjev (Kable Mai, 1968; Willis and Thompson, 1969), Xiphinema americanum Cobb (Lownsbery and Maggenti, 1963), and Heterodera glycines (Heatherly et al., 1982; Young and Heathery, 1988). Eggs of Meloidogyne hapla Chitwood hatched equally at field capacity and permanent wilting point of soil, but the hatched nematodes were unable to migrate in the drier soil (Couch and Bloom, 1960). Similar results were reported for Heterodera schachtii Schmidt (Wallace, 1955). WalL.G. Heatherly, USDA-ARS, oybean Prod. Res. Unit, P.O. Box 343, Stoneville, MS 38776; and L.D. Young, USDA-ARS, Nematology Res., 605 Airways Blvd., Jackson, TN 38301. Received 16 Feb. 1990. *Corresponding author. Published in Crop Sci. 31:191-196 (1991). Lawrence D. Young lace (1958a,b) showed that distribution of soil water in the pores is an important factor in movement of juveniles of H. schachtii and Ditylenchus dipsaci (Ktihn) Filipjev. Slack et al. (1972) reported that wellwatered soil allowed H. glycines to maintain infectivity for a significantly longer period. Reduced development of H. glycines as indicated by low cyst numbers in an excessively wet (-18 kPa soil water potential) sandy loam soil (Heathery et al., 1982) be interrelated with limited O2 level (Robbins and Barker, 1974; Wallace, 1955), fungal parasitism (Kerry et al., 1980), or reduced juvenile emergence from cysts (Slack and Hamblen, 1961). Soil texture and its inherent properties of pore and particle size, and soil water holding properties are important factors that influence nematode behavior and damage potential. Soil type influences the damage potential of P. penetrans (Schmitt and Barker, 1981), brachyurus (Godfrey) Filipjev (Schmitt and Barker, 1981), Meloidogyne incognita (Kofoid and White) Chitwood (Windham and Barker, 1986), and M. javanica (Treub) Chitwood (Sleeth and Reynolds, 1955). Heterodera glycines damage to soybean is dependent on sand or clay content of soil (Dropkin et al., 1976 ~, Koenning et al., 1988; Schmitt et al., 1987). Todd and Pearson (1988) recovered higher numbers of H. glycines females and eggs from a sandy loam soil than from silty loam soils 8 wk after introduction of similar numbers of eggs and juveniles; however, females and cysts increased in both soil types. Increased clay content adversely affects the mobility and distribution of M. incognita (Noe and Barker, 1985; Prot and Van Gundy, 1981), although the presence of some clay seemed preferable for nematode movement. Wallace (1958a) determined that H. schachtii is more mobile when pore diameter is 30 to 60 gm, which is larger than most pores in a clay soil (Danielson and Suthedand, 1986). Movement of both H. schachtii and D. dipsaci is dependent on soil particle size, but the soil particle size associated with maximum obility varies with species (Wallace, 1958b). Distribution of Belonolaimus longicaudatus Rau is limited to soils with >80% sand and < 10% clay content, and this is apparently the primary limiting factor in its geographical distribution (Robbins and Barker, 1974). Norton et al. (1971) found that density of Helicotylenchus pseudorobustus (Steiner) Golden was positively correlated with clay content, but Ferris and Bernard (1971) found a negative correlation for X. americanum and H. pseudorobustus in soybean fields. There are ~7.8 million ha of land in the lower Mississippi River alluvial flood plain. About 50% of this area is comprised of soils that are predominantly clay (Brown et al., 1970), and the majority of this large day area is planted to soybean. In fact, soybean is relegated primarily to these clay soils. There are no documented problems caused by H. glycines on this clay soil, but the assumption is that major problems caused by SCN 191 Published January, 1991