thickness ( Aldrich, 1984 ; Ozores-Hampton, 1998 ). Mulches inhibit weed growth by excluding light from the soil surface providing a physical barrier to weed seedling emergence ( Bond and Grundy, 2001 ) and also may include mechanisms including the release
Nicole Burkhard, Derek Lynch, David Percival, and Mehdi Sharifi
There are approximately 17,000 acres of fresh market vegetables and potatoes being produced on Long Island where irrigation is a routine agricultural production practice. Irrigation water is obtained from individual wells which pump water from an extensive underground aquifer. Although the quantity of water available for irrigation is not limited at present and will not be in the foreseeable future, the combination of agricultural practices, sandy soils and low soil pH's have had an impact on water quality. Certain pesticides move easily through the porous Long Island soils and are not quickly broken down at the naturally low pH levels of these soils. The use of Temik (aldicarb) for potato production resulted in ground water contamination with this chemical and spurred action by horticultural researchers and county and state agencies to define the scope of, and provide a potential solution for, contamination of Long Islands ground water. Thus, considerable effort has been expended on research and implementation programs to prevent ground water contamination with agricultural chemicals. Much of this effort has involved attempts to alter cultural practices, such as irrigation and pesticide application methods in order to decrease the potential for leaching of contaminants into the ground water. In addition, alternate crops have been considered which may require less irrigation and fewer pesticides than those traditionally grown. Specific research projects and government agency policies pertaining to agricultural water usage on Long Island will be discussed.
John S. Selker
Avoiding groundwater contamination from agricultural activities is possible only if the processes that control deep percolation are understood. The source of contaminant movement to groundwater is typically through preferential flow, processes by which the bulk soil is bypassed by some part of the infiltrating water. Three mechanisms give rise to preferential flow: fingered flow, funnel flow, and macropore flow. Fingered flow occurs in coarse-textured soils and can be minimized by starting with an initially well-wetted profile. Funnel flow is likely in layered soil profiles of silt or coarser-textured soil, in which avoiding slow overirrigation is critical. Macropore flow is observed in all structured soils in which maintaining irrigation rates well below the saturated conductivity of the soil is essential. These prescriptions are quite different than conventional recommendations, which fail to consider groundwater protection.
Timothy L. Creger and Frank J. Peryea
Fruit trees grown in soils contaminated with lead arsenate (PbHAsO4) pesticide residues are subject to arsenic (As) phytotoxicity, a condition that may be exacerbated by use of phosphate fertilizers. A potted soil experiment was conducted to examine the influence of phosphate fertilizer on accumulation of As and lead (Pb) in apricot (Prunus armeniaca) seedlings grown in a lead arsenate-contaminated Burch loam coil. Treatments were fertilizer source (mono-ammonium phosphate [MAP], ammonium hydrogen sulfate [AHS]) and rate (0, 8.7, 17.4, and 26.1 -mmol/liter), and presence/absence of lead, arsenate contamination (231 -mg/kg coil). Plant biomass accumulation was reduced by lead arsenate presence and by high fertilizer rates, the latter due to soil salinization. Phytoaccumulation of As was enhanced by lead arsenate presence and by increasing MAP rate but was not influenced by AHS rate, salinity, or acidity of soil. Phytoaccumulation of Pb was enhanced by lead arsenate presence but was not influenced by fertilizer treatment.
Warren C. Stiles
Concerns about the impacts of agricultural practices on the environment dictate that all management techniques must be examined from the perspective of minimizing such impacts. Integrated pest management practices such as scouting, use of biological controls, improvement of pesticide application techniques, tree-row-volume spraying, and consideration of the environmental impact of alternative chemical controls offer opportunity for minimizing the adverse impact of pesticides. Improved spray equipment with canopy sensors and spray recovery systems improve deposition and reduce pesticide waste. Applying nutrients on the basis of need as indicated by leaf and soil analyses offers the best means of assuring optimal crop performance and minimizing the potential for contamination of surface and ground water supplies. Soil management practices must be evaluated for their potential to minimize soil erosion and competition, and for their potential contribution to pest management. Ground covers that are nonsupportive of nematodes, disease, or insect pest populations merit additional research. Methods for managing ground covers with low rates of growth regulators or herbicides to minimize invasion by problem weeds, reduce the need for mowing, and regulate competition, while retaining their beneficial attributes in minimizing soil erosion and maintaining soil structure, would be advantageous to orchardists and the environment.
Qingren Wang, Yuncong Li, and Waldemar Klassen
A pot experiment with summer cover crops and soil amendments was conducted in two consecutive years to elucidate the effects of these cover crops and soil amendments on `Clemson Spineless 80' okra (Abelmoschus esculentus) yields and biomass production, and the uptake and distribution of soil nutrients and trace elements. The cover crops were sunn hemp (Crotalaria juncea), cowpea (Vigna unguiculata), velvetbean (Mucuna deeringiana), and sorghum sudangrass (Sorghum bicolor × S. bicolor var. sudanense) with fallow as the control. The organic soil amendments were biosolids (sediment from wastewater plants), N-Viro Soil (a mixture of biosolids and coal ash, coal ash (a combustion by-product from power plants), co-compost (a mixture of 3 biosolids: 7 yard waste), and yard waste compost (mainly from leaves and branches of trees and shrubs, and grass clippings) with a soil-incorporated cover crop as the control. As a subsequent vegetable crop, okra was grown after the cover crops, alone or together with the organic soil amendments, had been incorporated. All of the cover crops, except sorghum sudangrass in 2002-03, significantly improved okra fruit yields and the total biomass production (i.e., fruit yields were enhanced by 53% to 62% in 2002-03 and by 28% to 70% in 2003-04). Soil amendments enhanced okra fruit yields from 38.3 to 81.0 g/pot vs. 27.4 g/pot in the control in 2002-03, and from 59.9 to 124.3 g/pot vs. 52.3 g/pot in the control in 2003-04. Both cover crops and soil amendments can substantially improve nutrient uptake and distribution. Among cover crop treatments, sunn hemp showed promising improvement in concentrations of calcium (Ca), zinc (Zn), copper (Cu), iron (Fe), boron (B), and molybdenum (Mo) in fruit; magnesium (Mg), Zn, Cu, and Mo in shoots; and Mo in roots of okra. Among soil amendments, biosolids had a significant influence on most nutrients by increasing the concentrations of Zn, Cu, Fe, and Mo in the fruit; Mg, Zn, Cu, and Mo in the shoot; and Mg, Zn, and Mo in the root. Concentrations of the trace metal cadmium (Cd) were not increased significantly in either okra fruit, shoot, or root by application of these cover crops or soil amendments, but the lead (Pb) concentration was increased in the fruit by application of a high rate (205 g/pot) of biosolids. These results suggest that cover crops and appropriate amounts of soil amendments can be used to improve soil fertility and okra yield without adverse environmental effects or risk of contamination of the fruit. Further field studies will be required to confirm these findings.
Thomas F. Morris, George Hamilton, and Sara Harney
There is little published data to support current recommended plant populations of 11,500 to 17,500 plants/acre (28,600 to 34,600 plants/ha) for fresh market sweet corn (Zea mays L.) in the northeastern United States. The plant population likely affects marketable yield and recovery of nitrate. Residual soil nitrate is of concern because of the potential for nitrate contamination of water supplies. Our objectives were to determine the effect of plant population on the yield of sweet corn grown for fresh market without irrigation and on the amount of nitrate in the surface 1 ft (30 cm) of soil at harvest. Seven main-season sweet corn varieties were planted in a total of eight experiments in 1995, 1996, and 1997. Seven experiments were in Connecticut and one was in New Hampshire. All but one of the varieties were standard (su) or sugary enhanced (se) varieties. The experimental design was a randomized complete block with four replications, and the treatments consisted of 12,000, 16,000, 20,000, 24,000, and 28,000 plants/acre (29,600, 39,500, 49,400, 59,300, and 69,200 plants/ha). The yield of marketable ears was classified based on the length of the ears. The results suggest that the current recommendations for plant population in the Northeast US may be too low. Populations of 20,000 and 24,000 plants/acre produced consistently greater yields of ears greater than 7.0 inches (178 mm) long. Soil nitrate-N concentrations at harvest were about 8 mg·kg-1 lower with 16,000 plants/acre or greater, compared with 12,000 plants/acre, which suggests that populations of 16,000/acre or greater should decrease the potential for nitrate contamination of water supplies in the fall, winter, and early spring.
H.H. Krusekopf, J.P. Mitchell, T.K. Hartz, D.M. May, E.M. Miyao, and M.D. Cahn
Overuse of chemical N fertilizers has been linked to nitrate contamination of both surface and ground water. Excessive fertilizer use is also an economic loss to the farmer. Typical N application rates for processing tomato production in California's Central Valley are 150-250 kg·ha-1, and growers generally fail to fully consider the field-specific effects of residual soil NO3-N concentration, or N mineralization potential of the soil. The purpose of this research was to determine the effects of sidedress N fertilizer application, residual soil NO3-N, and in-season N mineralization, on processing tomato yield. Research was conducted during the 1998 and 1999 growing seasons at 16 field sites. Pre-sidedress soil nitrate concentration was determined at each trial site to a depth of 1 m, and aerobic incubation tests were conducted on these soils (top 0.3 m depth) to estimate N mineralization rate. Sidedress fertilizer was applied at six incremental rates from 0 to 280 kg N/ha, with six replications of each treatment per field. Only five fields showed yield response to fertilizer application; yield response to fertilizer was associated with lower pre-sidedress soil nitrate levels. In most fields with fertilizer response, yield was not increased with sidedress N application above 56 kg·ha-1. Mineralization was estimated to contribute an average of ≈60 kg N/ha between sidedressing and harvest. These results suggest that N fertilizer inputs could be reduced substantially below current industry norms without lowering yields, especially in fields with higher residual soil nitrate levels.
Michael P. Croster and John B. Masiunas
Studies established the critical period for eastern black nightshade (nightshade) (Solanum ptycanthum Dun.) competition in pea (Pisum sativum L.) and determined the effect of N fertility on pea and nightshade growth. In 1992, pea yields were most affected when nightshade was established at planting and remained for 4 or 6 weeks, while in 1993, competition for 6 weeks caused the greatest reduction in pea yields. In a sand culture study, pea biomass and N content were not affected by three N levels (2.1, 21, and 210 mg·L-1). Nightshade plants were five to six times larger in the highest N treatment than at lower N levels. Nitrogen content of nightshade was 0.76% at 2.1 ppm N and 3.22% at 210 ppm N. Choosing soils with low N levels or reducing the N rates used in pea may decrease nightshade interference and berry contamination of pea.
Monte L. Nesbitt, J. Benton Storey, D. Lyda, and L.J. Grauke
Rootstock resistance to soil-borne phytopathogenic fungi, such as Phymatotrichum omnivorum (Shear) Duggar, is an important factor in disease control. Measurement of natural rootstock resistance is often based on plant survival/mortality percentage, and /or growth data. Fungal colonization of host roots in disease screening experiments may not be uniform for many reasons, causing variability in host response. Quantification of fungal colonization is needed in order to better understand rootstock performance. Ergosterol, a structural sterol in cell membranes of fungi, is not found in higher plants, and can thus be a measure of fungal colonization. Ergosterol was extracted from roots of pecan seedlings artificially inoculated with P. omnivorum and grown in an environmental growth chamber. Analysis of extracts with HPLC revealed that seedlings which were killed in screening, or had low root performance ratings, had increased levels of ergosterol. Non-inoculated controls also contained Ergosterol. indicating contamination and possible competition by other fungi.