K. R. Barker

Influences of organic and synthetic soil fertility amendments on nematode trophic groups and community dynamics under tomatoes

Abstract Research was conducted to examine the effects of organic and synthetic soil amendments and tillage on nematode communities in field soils planted to tomato ( Lycopersicon esculentum ) at two locations. The experimental design was a replicated split plot with chisel-plow tillage and bare-soil or chisel-plow tillage and surface mulch with wheat straw as main plots, and soil amendments of synthetic fertilizer, composted cotton-gin trash, swine manure, or a rye-vetch green manure as subplots. Tillage did not affect free-living or plant-parasitic nematode community dynamics, but soil amendments had a large impact on nematode community structure and diversity. Populations of bacterivorous nematodes mainly in the Rhabditidae and Cephalobidae, and fungivorous nematodes were greater after planting in soils amended with swine manure, composted cotton-gin trash, or rye-vetch, than in soils amended with synthetic fertilizer at both locations. Populations of nematodes in these trophic groups decreased through time in each year. Populations of Meloidogyne incognita in soil were not affected by soil amendments, but increased through time at each location. Root-gall indices were lower in plots containing swine manure or cotton-gin trash than in those with synthetic fertilizer or rye-vetch during the second season. The combined nematode maturity index values were greater at planting in soils amended with rye-vetch or fertilizer than in soils with swine manure and composted cotton-gin trash. Shannon’s diversity index decreased over time for both years at one location, regardless of soil amendment. At the second location, the Shannon’s diversity index decreased only in the second year. Use of descriptive indices, including the Enrichment index, structure index, and channel index provided useful information about the effects of organic amendments on the structure of nematode communities in tomato field soils.

Impact of crop rotation and tillage system on Heterodera glycines population density and soybean yield.

The long-term effects of no-till planting practices and rotation on the population dynamics of the soybean cyst nematode (Heterodera glycines) and soybean yield were investigated in field experiments over a period of 8 yr. The experiment was a 2 X 4 factorial, comparing no-till vs. conventional tillage practices in four cropping patterns (continuous soybean, a 1-yr rotation of corn and soybean, a rotation of 2 yr of corn followed by soybean, and a corn-wheat/soybean double-cropping system). Treatments were arranged so that each combination occurred every year after 1986. Soybean after 1 yr of corn had higher yields (P = 0.0001) than soybean after soybean. Two years of corn between soybean crops resulted in soybean yields higher than those after 1 yr of corn in only 2 out of 6 yr. The yields of soybean in the corn, wheat/soybean double-cropping system, however, were generally similar to monoculture soybean. No-till practices had positive or no effects on soybean yield early in the study, but yields of no-till soybean were lower (P = 0.01) than conventionally tilled soybean after several years because weed pressure was greater in no-till plots. Population densities of H. glycines were greater (P < 0.10) in conventionally tilled plots than in no-till plots in 1988 and 1990-1992. Numbers of H. glycines fluctuated in an unpredictable manner from year to year, possibly because of unidentified biological control agents or excessive moisture in certain years. H. glycines population densities declined in a predictable manner when a nonhost was planted

The role of low molecular weight organic acids from decomposing rye in inhibiting root-knot nematode populations in soil

Organic soil amendments have been employed as an alternative to or in combination with, chemical nematicides and cultural practices to control plant-parasitic nematodes. Rye ( Secale cereale L.) has been shown to be effective in minimizing the damage caused by root-knot nematodes (Meloidogyne incognita(Kofoid and White) Chitwood) when grown as a cover crop and then incorporated into the soil prior to planting. It has been suggested that the release of low molecular weight organic acids during the decomposition of rye is the cause of the nematicidal effects. This study was conducted to quantify the concentration and persistence of formic, acetic, propionic, butyric, and valeric acids in soil solution following the incorporation of fresh rye foliage. Formic and acetic acids were detected by means of ion exclusion chromatography, primarily in the first 24 h following addition of rye, and at concentrations <450mmol/l. The effect of the rye treatment on the root-knot nematode population was determined by growing tomato plants (Lycopersicon esculentumMill.) in the rye-amended soil and assessing the nematode damage to the root systems. Despite the low concentrations of organic acids detected, the rye treatment resulted in a significant suppression of root-knot nematode activity. To determine the fate of these acids in soil, an addition of each acid was made to a field soil resulting in a soil water concentration of 1500 mmol/l for each acid. Soil solution samples were collected every 2 h for 10 h and analyzed for the five added organic acids by means of ion exclusion chromatography. The concentration of all acids declined by 54‐97% over the 10 h incubation. Although low molecular weight organic acids may be one of many factors that contribute to restriction in root-knot nematode damage, these acids do not appear to be solely responsible for the nematicidal effect of the rye.

Effects of cropping systems on population density of Heterodera glycines and soybean yield

We evaluated the effects of soybean planting date and maturity group (MG) on final population density of Heterodera glycines and yield in cultivars susceptible to H, glycines grown in monoculture and in rotations with 1 or 2 yr of nonhosts. Population density of eggs and eggs plus second-stage juveniles of H. glycines declined to barely detectable levels after 2 yr of nonhost culture. Population densities of this nematode were consistently greater (P=0.05) for an MG VII cultivar than an MG V cultivar. Planting date had variable effects on final population density of H. glycines: early planting resulted in the highest nematode numbers in some years, whereas late planting was associated with significantly greater (P=0.05) population densities in other years

Effects of Rate and Time of Application of Poultry Litter on Hoplolaimus columbus on Cotton

Field experiments were conducted to evaluate the effect of soil-incorporated poultry litter on the population dynamics of Hoplolaimus columbus and cotton lint yield. Rates of poultry litter applied varied from 0.0 to 27.0 t/ha and were applied in December, February, or March. Time of application did not influence population densities of this nematode or cotton yield. The rate of poultry litter applied was negatively related to the population density of H. columbus at midseason, but not at other sampling dates. The lower midseason levels of this nematode corresponded with increases in cotton lint yield in all experiments. Cotton yield increases generally were linear with respect to the rate of litter applied, although the highest rates of litter applied did not always result in the greatest cotton yield. Poultry litter can be used effectively to supply nutrients to the crop and suppress damaging levels of H. columbus. Optimal rates of litter application were from 6.0 to 13.4 t/ha. Application of poultry litter at these rates, however, may exceed nutrient levels required for best management practices.