Winter rapeseed performance in the southeastern Coastal Plain

Fifty-five rapeseed (Brassica napus L.) cultivars were evaluated between 1982 and 1987 on a Norfolk loamy sand (fine, loamy, siliceous, thermic Typic Paleudult) near Florence, South Carolina. The average seed yield (1,590 kg/ha or 1,420 pounds/acre) was comparable to that at other southern locations where rapeseed is grown as a winter annual, but it was lower than in the Pacific Northwest, where the crop is grown as a true biennial. Assuming a contract price of $0.2011cg ($0.09/pound), estimated gross returns for rapeseed would be about $320/ha 0130/acre). For conservation purposes, the crop may be more valuable because of its potential to reduce soil erosion; rapeseed provides soil surface cover at an earlier date than winter wheat (Triticum aestivum L.). Results of this evaluation suggest that additional research is needed to evaluate rapeseed as a winter forage and/or cover crop for soil erosion control

Implement and soil condition effects on tillage-induced erosion

Water, wind, or tillage-induced soil erosion can significantly degrade soil quality. Therefore, understanding soil displacement through tillage translocation is an important step toward developing tillage practices that do not degrade soil resources. Our primary objective was to determine the effects of soil condition (i.e. grassland stubble versus previously tilled soil), opening angle, and harrow speed on soil translocation. A second field study also conducted on a Lixisol but only in the stubble field, quantified displacement effects of mouldboard ploughing. The field studies were located 12 km South of Évora, Portugal. Soil displacement or translocation after each tillage operation in both studies was measured using aluminium cubes with a side length of 15mm as ‘tracers’. Offset angles for the harrow disk were 20◦, 44◦ and 59◦; tractor velocities ranged from 1.9 to 7.0 km h−1 and tillage depth ranged from 4 to 11 cm. The depth of mouldboard ploughing was approximately 40 cm with a wheel speed of 3.7 km h−1. The translocation coefficients for the two implements were very different averaging 770 kgm−1 for the mouldboard plough and ranging from 9 to 333 kgm−1 for the harrow disk. This shows that the mouldboard plough was more erosive than the harrow disk in these studies. All three variables (soil condition, opening angle, and tillage velocity) were critical factors affecting the translocation coefficient for the harrow disk. Displacement distances were the largest for compacted soils (stubble field), with higher opening or offset angles, and at higher velocities. The results also showed significant correlation for (a) mean soil displacement in the direction of tillage and the slope gradient and (b) soil transport coefficient and the opening angle. Our results can be used to predict the transport coefficient (a potential soil quality indicator for tillage erosion) for the harrow disk, provided tillage depth, opening angle, and tool operating speed are known

Soil quality improvement through conversion to sprinkler irrigation

Conversion from furrow to sprinkler irrigation is a recommended conservation practice for improved water use efficiency (and/or erosion control), but effects on soil quality indicators were unknown. Several soil quality indicators were therefore quantified within a northwestern U.S. Conservation Effects Assessment Project (CEAP) watershed after changing from long-term furrow to sprinkler irrigation. Four on-farm sites were identified where producers were growing irrigated barley (Hordecum vulgare L.) using both irrigation practices. Climate, soil type, and management were similar between sites. Soil samples were collected from the upper and lower ends of furrow irrigated fields at three in-field positions (bed, shoulder, and furrow); fields converted to sprinkler irrigation were sampled where the upper and lower ends were when the field was furrow irrigated. Soil quality indices (physical, chemical, biological, nutrient, and overall) were computed using the Soil Management Assessment Framework (SMAF). Regardless of in-field position, furrow irrigated field bottoms had higher soil quality index scores than field tops due to long-term erosional deposition. Within sprinkler irrigated fields, soil quality indices for field tops and bottoms showed minimal differences. Overall, when all sampling locations and in-field positions were combined, soil quality was similar for both irrigation methods. However, as compared to furrow irrigation, sprinkler irrigation had greater soil quality indices in the field tops, suggesting that sprinkler irrigation improved soil quality of historically eroded furrow irrigated fields

Alternative N fertilizer management strategies effects on subsurface drain effluent and N uptake

Demonstrating positive environmental benefits of alternative N fertilizer management strategies, without adversely affecting crop growth or yield, was a major goal for the Midwest Management Systems Evaluation Areas (MSEA) program. Our project objectives within this program were to quantify the effects of split- and single-N fertilization strategies on NO3-N concentration and loss in subsurface drain effluent and N accumulation and yield of corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. The study was conducted on glacial till derived soils in northeast Iowa from 1993 through 1995 using no-till and chisel plow tillage treatments. One-third of the 2,611 effluent samples had NO3-N concentrations greater than 10 mg L-1 . Split applying fertilizer N based on pre-sidedress soil nitrate test (PSNT) results significantly increased corn yield for both tillage treatments in the extremely wet 1993 without increasing NO3-N loss in drain effluent. Increased grain yield also resulted in significantly more N removal. When fertilizer N was applied based on the PSNT, no-till and chisel treatments had similar NO 3-N losses and concentrations. Average flow-weighted NO3-N concentrations in drain effluent were not increased when larger amounts of fertilizer were applied based on PSNT. However, prior crop and tillage practices and differences in drain flow volume caused significant differences in NO3-N losses and concentrations. These results suggest that spatial differences in flow volume are a major factor determining NO3-N loss in drainage effluent. Significant differences suggest that combining no-tillage practices with split N fertilizer management strategies can have positive environmental benefits without reducing corn yield

A conservation tillage research update from the Coastal Plain Soil and Water Conservation Research Center of South Carolina: A review of previous research

In the U.S. Southeastern Coastal Plains conservation tillage (CT) became useful as a management system with the development of in-row subsoiling systems capable of planting into heavy residues. Research priorities associated with the development of CT included: reducing cover crop water loss, improving stand establishment, assessing nutrient and water management requirements, determining optimal subsoiling strategies, understanding long-term conservation tillage effects on soil properties, evaluating the interaction of crop residue removal with tillage systems, and documenting tillage impact on pests and beneficial organisms. Since the late 1970s the Coastal Plains Soil and Water Conservation Research Center in Florence, SC has made a concerted effort to study these interactions and alleviate them as obstructions to the use of CT management. These studies showed that for Coastal Plain soils such as Norfolk sandy loam ( fine-loamy, siliceous thermic, Typic Paleudults ) winter cover crops such as rye (Secale cereale L.) desiccated the soil profile by evapotranspiration in the spring. This delayed emergence and early season growth of corn (Zea mays L.) but not full-season soybean (Glycine max ( L. ) Merr. ). Conservation tillage helped manage soil strength by gradually increasing soil organic matter content, restricting traffic patterns and maintaining higher soil water contents. Laboratory studies demonstrated a negative correlation (R2=0.85 ) between proctor soil strength and organic matter content. Conservation tillage affected nematode, Bradyrhizobium japonicum and Heliothis species populations. Alternate cropping systems using rapeseed (Brassica napus L.) as a winter crop or sunflower (Helianthus annuus L.) either before soybean or after corn provided crop cover against potential soil loss from late autumn through early spring, when bare soil is exposed to intense rainfall. Water quality questions associated with CT have been raised but remain unanswered. Although CT can reduce runoff and erosion, the crop residues can support higher insect populations and pathogen inoculum levels, and thus prompt greater pesticide use. Quantifying relationships between soil strength, macropore formation and persistence, and water infiltration with surface and subsurface water quality is the focus of new long-term evaluations. The findings of these studies, published to date, are summarized in this paper

Bragg soybeans grown on a Southern Coastal Plain soil. IV. Seasonal changes in nodal N and P concentrations

Determinate soybean [Glycine max (L.) Merr.] has been characterized by few detailed nitrogen and phosphorous partitioning studies. Knowledge of the variation in N and P concentrations with plant part, nodal position, and plant age is needed for a better understanding of plant functions. In this field study, 'Bragg' soybean was grown on an Aquic Paleudult soil (series Goldsboro loamy sand). Plants were sampled at 10 to 14 day intervals beginning 44 days after planting (July 7) until harvest. Maximum observed N concentrations were 3.1, 2.8, 5.8, and 5.4% for stem internodes, petioles (+branches), leaf blades, and pods, respectively. Maximum observed P concentrations were 0.34, 0.48, 0.78, and 0.52 for the same respective plant parts. Nodal and temporal mean N and P concentrations varied considerably with plant age and nodal position in all plant parts. These data show that mean N and concentrations in all four plant parts can vary several fold, depending upon plant age and nodal position for the sample. This suggests caution should be exercised in tissue sampling and interpretation of plant analysis. Concentrations of N and P generally decreased with time for stem internode, petioles (+branches), and leaf blades, but increased with time for pods. Except for N concentration in stem internodes, which increases with internode number, the N and P concentrations remain nearly constant throughout the growing season. The relationships provide insight for developing accurate plant models depicting N and P concentrations and translocations over time and among plant parts in determinate soybean

A decade of progress in conservation tillage in the South Carolina Coastal Plain

Stream discharge measurements with chemical dilution techniques have been proposed in several forms since the beginning of this century (Groat4). Early techniques consisted of introducing a chemical, usually brine, at a known rate into flowing water and determining the resulting concentration of the chemical in the stream at a section far enough downstream to assure adequate mixing of the chemical with the water. A variation of this method, and the technique used in the present study, was described by Barbagelata5 in 1928. In that method, a known quantity of tracer was added, as a slug, to the stream to be measured. At a sampling station sufficiently far downstream for adequate lateral mixing, the tracer concentration-time curve was determined. The stream discharge was then calculated from the amount of tracer added and the area measured under the curve

Planting geometries and the efficient use of water and nutrients

In nature and in the most primitive agricultural systems, seed distribution is broadcast across the landscape. Such a distribution results in nearly uniform spacial interaction of the developing phytomass. With the development of agrarian civilization has come an implement-dependent systemization of crop- planting patterns. This has brought about the planting of crops in uniform rows—from the drilling of small grains at inter-row spacings of 0.1 to 0.2 m and plant intra-row spacings of i to 5 cm, to the staking of horticultural and vine crops at 2- to 3—m inter-row spacings and typically 0.3- to l-m intra-row spacings. The implement dependence of agricultural cropping strategies has resulted in row cropping. The staple crops regarded as most suited to this approach are commonly called row crops, and this review will concentrate largely on how row crops interact with plant geometry, water, and nutrients to in?uence sustained productive capacity

Soil and plant response to three subsoiling implements

Many Southeastern Coastal Plain soils require deep (>0.45 m) inrow tillage or subsoiling to disrupt dense tillage/traffic pans and/ or eluvial (E) horizons. Three subsoiling implements [Super Seeder (SS), ParaTill (PT), and Kelly (KE)] were compared on Norfolk (Typic Paleudult) loamy sand to assess their effectiveness in developing and maintaining a proper rooting environment for corn (Zen mays L.). Soil strength (cone index) for the implements was evaluated with and without conventional surface tillage (disking). All three subsoiling implements effectively disrupted the E horizon regardless of surface tillage, but the 67% stand establishment in nondisked treatments was significantly lower than for disked treatments (92%). However, yields were not significantly different. Significant differences in soil strength were measured among subsoiling implements at the beginning of each growing season. In 1985 mean profile soil strength was lower (P 0.10) for SS and PT than for KE. In 1986, soil strength was lower (P 0.10) for SS than either PT or KE. The consistent difference between SS and KE occurred because SS disrupted a larger area than the thinner-shanked KE. Nondisked treatments had mean soil strength that was 0.32 MPa lower within the row than disked treatments, but disked treatments had mean soil strength that was 0.37 MPa lower between the rows. Soil strength results suggest that Coastal Plain soils, which have been subsoiled, are less likely to restrict root development regardless of implement with, or without, prior surface tillage

Irrigation management for double-cropped fresh-market tomatoes on a high-water-table soil

Two tomato (Lycopersicon esculentum, Mill.) experiments were conducted for two years on a southeastern Coastal Plain soil that has a high, fluctuating water table. In one experiment, two methods for managing microirrigation were compared to a treatment that received only rainfall by measuring marketable fruit yields for spring and fall cropping seasons. Irrigation increased yields for both seasons in the second year because of low rainfall. Measurements among seven shallow wells on the site showed no consistent differences for either water table depth or gradient between adjacent wells. Two cultivars were evaluated in the second year, primarily because frost severely damaged the tomato plants about three weeks after transplanting. In the second experiment, two excessively irrigated treatments were evaluated in an effort to induce a "soft-fruit" storage and shipping problem experienced by many growers in this region. Although extremely large quantities of irrigation water were applied, these symptoms were not observed in this study. There were no differences in fruit yield between the two water management treatments in either spring or fall. Fruit quality measurements showed no significant differences. The 'Sunny' cultivar performed better than 'Walter' during the fall season for the extremely wet soil condition. A double-crop, microirrigation management system has higher input costs but provides increased profitability for fresh-market tomato production, particularly where markets are available for both spring and fall crops