John H. Grove

Disruptive methods for assessing soil structure

The description and quantification of soil structure is very important because of the many agronomic and environmental processes related to the arrangement of secondary soil units (aggregates, peds or clods) and their stability. The purpose of this review is to present and discuss methods and indices used to characterize soil structure based on the size distribution and stability of fragments produced by breaking apart the soil matrix. The size of fragments is inversely related to the mechanical stress applied. Thus, the selection of an appropriate fragmentation procedure is critical if information on soil structure is to be recovered, and often depends upon the soil process of interest. Soil fragmentation starts at sampling in the field and continues during laboratory separation of soil units by sieving. It is useful to characterize the fragment mass-size distribution with parameters from a model, such as the log-normal distribution function. Fractal theory provides a physically based link between the size distribution and stability of fragments. Structural stability is based on the ratio of fragment mass-sizes measured before and after low and high mechanical stresses, respectively. Thus, an adequate description of the applied stress conditions is essential for the parameterization of structural stability as well as the fragment mass-size distribution.

Release and recovery of nitrogen from winter annual cover crops in no‐till corn production

Abstract The rate and temporal pattern of ? mineralization from decomposing residues of hairy vetch (Vicia villosa Roth) and rye (Secale cereale L.) were compared with the pattern of ? uptake by corn (Zea mays L.) planted under no‐tillage into these cover crops in the field. In a second field study where no corn crop was grown, the pattern of ? mineralization from killed fescue sod was compared with the pattern from killed hairy vetch plus sod. Hairy vetch was far more effective than rye in supplying corn ? requirements. In both experiments, the majority of ? mineralized during the corn growing season became available only after a period corresponding to corn silking. The results suggest poor synchronization between ? release via cover crop mineralization and corn ? uptake in the no‐till system.

Nitrogen Fertilization Suppresses Soil Phenol Oxidase Enzyme Activity In No-tillage Systems

Phenol oxidase is associated with the carbon cycle and its presence in soil environments is important to the formation of humic substances. Little effort has been made to integrate the response of phenol oxidases with soil management. We investigated phenol oxidase activity on a Maury silt loam (fine, mixed, mesic Typic Paleudalfs) soil after 33 years of imposed tillage and N fertilization treatments. Particle size fractions were investigated independently to help identify the location of the enzyme. Phenol oxidase activity was 1.7 times greater (P < 0.01) in no-tillage (NT) compared with moldboard plow (MP) in the control treatment (0 kg N ha−1), consistent with the known effects of tillage. The phenol oxidase was located primarily in the silt fraction, followed by the clay and sand in the NT. In NT, N fertilization (336 kg N ha−1) had a marked negative effect on soil phenol oxidase activity, showing a 38% decrease (P < 0.01) despite the increase in soil organic carbon (SOC). In contrast, MP plots were relatively insensitive to applied N rate. Phenol oxidase activity was related negatively to dissolved inorganic nitrogen (DIN) (r = −0.49, P < 0.1), SOC (r = −0.49, P < 0.1) and dissolved organic carbon (r = −0.51, P < 0.1) in NT. This research provides new information about the response of phenol oxidase enzymes to long-term N fertilization in NT and MP systems. These findings suggest that manipulating the application rates of fertilizer N in soils under NT will make it possible to impact phenol oxidase activity.

Arsenic species in broiler (Gallus gallus domesticus) litter, soils, maize (Zea mays L.), and groundwater from litter-amended fields

Manure and bedding material (litter) generated by the broiler industry (Gallus gallus domesticus) often contain high levels of arsenic (As) when organoarsenical roxarsone and p-arsanilic acid are included in feed to combat disease and improve weight gain of the birds. This study was conducted to determine As levels and species in litter from three major broiler producing companies, and As levels in soils, corn tissue (Zea mays L.), and groundwater in fields where litter was applied. Total As in litter from the three different integrators ranged between <1 and 44 mg kg(-1). Between 15 and 20% of total As in litter consisted of mostly of arsenate, with smaller amounts of roxarsone and several transformation products that were extractable with phosphate buffer. Soils amended with litter had higher levels of bioavailable As (extractable with Mehlich 3 solution and taken up by corn leaves). Arsenic concentrations in plant tissue and groundwater, however, were below the World Health Organization thresholds, which was attributed to strong sorption/precipitation of arsenate in Fe- and Al-rich soils. Ecological impacts of amending soils with As-laden litter depend on the As species in the litter, and chemical and physical properties of soil that strongly affect As mobility and bioavailability in the environment.

Correcting soil acidification in continuous corn (Zea mays L.): N rate, tillage and time

Abstract Use of ammoniacal N in continuous corn production results in greater acidification of the surface soil layer under conservation tillage. Moldboard plowing results in dilution of acid inputs to greater depth. The objective of this work was to observe soil reaction after a lime application made to a continuous corn experiment initiated in 1970. Four fertilizer N rates (0. 84. 168. and 336 kg N ha‐1) and two primary tillage systems (no‐tillage and moldboard plowing) were used. Lime application was made to half of each plot in 1983. Control of developed acidity was achieved the first year on the plowed soil. This was not the case on the most acid no‐till soil, where both corn dry matter production and leaf Mn concentration also indicated persistence of acidity. Surface lime application resulted in soil pH changes limited to the upper 10 cm of no‐till soil. Shallow incorporation of lime may be needed to more quickly control strongly developed acidity in no‐till soils.

Sustaining Soil Quality with Legumes in No-Tillage Systems

Abstract Tillage, cropping system, and cover crops have seasonal and long‐term effects on the nitrogen (N) cycle and total soil organic carbon (C), which in turn affects soil quality. This study evaluated the effects of crop, cover crop, and tillage practices on inorganic N levels and total soil N, the timing of inorganic N release from hairy vetch and soybean, and the capacity for C sequestration. Cropping systems included continuous corn (Zea mays L.) and stalk residue, continuous corn and hairy vetch (Vicia villosa Roth), continuous soybeans (Glycine max L.) plus residue, and two corn/soybean rotations in corn alternate years with hairy vetch and ammonium nitrate (0, 85, and 170 kg N ha−1). Subplot treatments were moldboard plow and no tillage. Legumes coupled with no tillage reduced the N fertilizer requirement of corn, increased plant‐available N, and augmented total soil C and N stores.

Spreading uniformity of granular bulk‐blended fertilizer

Abstract This study was conducted to measure the field variability in nutrient rate of bulk blended granular fertilizer that was spread with a double‐spinner, ground driven spreader. The objective was to determine if such variation affected corn (Zea mays L.) yield and nutrient concentrations. Studies were conducted at two sites in Kentucky during 1987 to test the agronomic effects of varying granule size of urea (U) and diammonium phosphate (DAP) when they were blended with muriate of potash (KC1) to prepare a bulk‐blended mixed fertilizer. The control (uniform blend) blend components were all of the same granule size (2.0–3.36 mm). Two blends of identical analysis were prepared by using smaller (1.4–2.0 mm) granule sized U (fine urea) or DAP. Each of the three blend treatments was spread in swath widths of 12.19 m. Measurements were made every 2.44 m across the swath to measure rate of nutrient application, 10‐leaf stage growth of corn, ear leaf, nutrient concentration of com, harvest stand population, ...

Nutrient uptake of corn grown using moldboard plow or no-tillage soil management

Abstract Crop nutrition under different tillage systems continues to be an issue. Corn (Zea mays L.) growth and nutrient (N, P, K, Ca, Mg) uptake were monitored for two years under either no‐tillage or conventional (moldboard plow plus disc) tillage management. Two rates of applied N (84, 168 kg N ha‐1) were imposed as well. The crop was planted in mid‐May, and sampled about 60 days after planting and at crop maturity. Grain yields were generally increased by the higher N application rate and by tillage reduction. Phosphorus, calcium, and magnesium uptake were generally unaffected by treatment. Total nitrogen recovery by the crop was lowered by no‐tillage soil management at the 84 kg N ha‐1 application rate, but was equal across tillage treatments at the 168 kg N ha‐1 rate. Potassium acquisition by the crop was strongly related to the surface stratification of K in the no‐till soil environment.

Alterations in soybean root development due to cultural practices: A review

Abstract The heterogeneous nature of the soil of the root zone will produce wide variations in soybean (Glycine max (L.) Merrill) root development. The effects of management practices on root development are not as well understood as are the effects of cultural practices on shoot development. General descriptions of soybean root system production are presented in the literature. Evidence has also been presented in support of the concept that soybean root development is a dynamic, self regulated process, controlled, in part, by the root zone environment. Numerous quantitative and qualitative techniques have been used to haracterize field rooting patterns, and significant differences in root production and distribution have been observed among soybean cultivars. The effect of planting date on soybean root production is primarily a combination of the effects of temperature, moisture, and photoperiod. Root growth appears to have a lower optimum temperature than shoot growth. Soybean possesses a great water up...

Denitrifying bacteria stratify above fragipans

Fragipans are impermeable layers in soil that affect more than 950,000 ha of land in Kentucky and create seasonally perched water tables that may promote denitrifier growth and activity. We used denitrification enzyme activity assays and Most Probable Number (MPN) estimates of soil and water samples