Nancy G. Creamer

CHANGES OVER TIME IN THE ALLELOCHEMICAL CONTENT OF TEN CULTIVARS OF RYE (Secale cereale L.)

Published studies focused on characterizing the allelopathy-based weed suppression by rye cover crop mulch have provided varying and inconsistent estimates of weed suppression. Studies were initiated to examine several factors that could influence the weed suppressiveness of rye: kill date, cultivar, and soil fertility. Ten cultivars of rye were planted with four rates of nitrogen fertilization, and tissue from each of these treatment combinations was harvested three times during the growing season. Concentrations of a known rye allelochemical DIBOA (2,4-dihydroxy-1,4-(2H)benzoxazine-3-one) were quantified from the harvested rye tissue using high performance liquid chromatography (HPLC). Phytotoxicity observed from aqueous extracts of the harvested rye tissue correlated with the levels of DIBOA recovered in harvested tissue. The amount of DIBOA in rye tissue varied depending on harvest date and rye cultivar, but was generally lower with all cultivars when rye was harvested later in the season. However, the late maturing variety ‘Wheeler’ retained greater concentrations of DIBOA in comparison to other rye cultivars when harvested later in the season. The decline in DIBOA concentrations as rye matures, and the fact that many rye cultivars mature at different rates may help explain why estimates of weed suppression from allelopathic agents in rye have varied so widely in the literature.

Killing cover crops mechanically: Review of recent literature and assessment of new research results

Cover-crop residues left on the soil surface as a mulch in no-till crop production systems protect the soil from erosion, increase water infiltration and suppress weeds. Because many growers using cover crops want to reduce chemical inputs, non-chemical methods of killing or suppressing cover crops are needed. In the first part of this paper we review the current literature and discuss advantages and disadvantages of five mechanical methods for killing cover crops, i.e., mowing, rolling, roll-chopping, undercutting and partial rototilling. We also report on three new studies that broaden the current literature, including planting into freshly killed residue. In the first study, the use of planter attachments to remove surface residues from the planter row improved stands when cotton was no-till planted 2-7 days after mowing cover crops in Mississippi. In the second study, 100% of a rye/vetch cover crop in Missouri was killed by mowing, and greater than 90% was killed by roll-chopping. Cotton stands were reduced by the use of row cleaners that clogged when the cover crop was roll-chopped or mowed on the same day that the crop was planted. The third study evaluated three methods of mechanically killing summer cover crops in North Carolina. Undercutting provided greater than 95% kill for five of six broadleaf species, and two of five grass species. Mowing effectively killed all six broadleaf cover crops, but re-growth occurred with three of five grasses, with the exception of nearly mature German foxtail millet and mature Japanese millet. In general, rolling did not effectively kill broadleaf or grass cover crops, with the exception of nearly mature German foxtail millet, mature Japanese millet and mature buckwheat.

Long-term Agricultural Research: A Research, Education, and Extension Imperative

ABSTRACT For agriculture to meet goals that include profitability, environmental integrity, and the production of ecosystem services beyond food, fuel, and fiber requires a comprehensive, systems-level research approach that is long-term and geographically scalable. This approach is largely lacking from the US agricultural research portfolio. It is time to add it. A long-term agricultural research program would substantially improve the delivery of agricultural products and other ecosystem services to a society that calls for agriculture to be safe, environmentally sound, and socially responsible.

Editorial: Overview and comparison of conservation tillage practices and organic farming in Europe and North America

Editorial: Overview and comparison of conservation tillage practices and organic farming in Europe and North America.

Critical Weed-Free Period for 'Beauregard' Sweetpotato (Ipomoea batatas)'

Studies were initiated at two different planting dates and conducted at two different locations in 2001 to determine the critical weed-free period for certain populations of weeds in organically produced ‘Beauregard’ sweetpotato. Naturally occurring weed populations were used, and they included sicklepod, redroot pigweed, and yellow nutsedge. Treatments included allowing weeds to grow for 2, 4, 6, or 8 wk after transplanting (WAT) sweetpotato before weed removal and maintaining the sweetpotato weed-free for 2, 4, 6, or 8 WAT. Weedy and weed-free checks were also included in the study. These treatments were used to determine the length of time weeds can compete with sweetpotato without reducing yield and the length of time sweetpotato must grow before yield is no longer affected by newly emerging weeds. Yield of number one grade sweetpotato roots best fit a quadratic plateau curve for the grow-back treatments and a logistic curve for the removal treatments. Yields in weed-free plots of sweetpotato were higher at the early planting date, whereas yields in plots of weedy sweetpotato were higher at the late planting date. Weed biomass was lower in the grow-back treatments at the late planting date. Data indicate that sweetpotato may gain a competitive advantage over weeds when planted at a later date. At both planting dates, a critical weed-free period of 2 to 6 WAT was observed. Nomenclature: Redroot pigweed, Amaranthus retroflexus L. #3 AMARE; sicklepod, Senna obtusifolia (L.) Irwin and Barneby # CASOB; yellow nutsedge, Cyperus esculentus L. # CYPES; sweetpotato, Ipomoea batatas (L.) Lam. ‘Beauregard’. Additional index words: Competition, interference, organic production, Brachiaria platyphylla, Eleusine indica, Mollugo verticillata, Sida spinosa, BRAPP, ELEIN, MOLVE, SIDSP. Abbreviations: WAT, weeks after transplanting.

Influence of seedpiece spacing and population on yield, internal quality, and economic performance of Atlantic, Superior, and Snowden potato varieties in eastern North Carolina

In recent stand assessment surveys on North Carolina farms, potato plant stands averaged only 67% of target populations. In response to these findings, this study was designed to determine the effects of seed-piece spacing and varying seedpiece populations on yield, internal quality, and economics of three potato varieties commonly grown in North Carolina: Atlantic; Snowden; and Superior. The three varieties responded differently to changes in spacing and population. Atlantic was sensitive to differences in spacing and populations, with reduced yields of grade A tubers as spacing increased above 23 cm. Atlantic was not able to compensate for wide (46 cm) spacing, even when seed-piece populations were high (doubles planted every 46 cm). Yield of B tubers was greater for 15 cm spacing and decreased significantly as spacing was increased. Yield of Superior was affected less by increases in spacing than decreases in population. Superior was able to compensate for wide gaps in spacing if seedpiece populations were high. Superior produced more B tubers at the 15 cm spacing, and less at the 46 cm spacing. Yield of grade A Snowden tubers did not differ with spacing or population; however, there were more B tubers in the 15 cm, 23 cm, and 46 cm (doubles) treatments than the wider spacing treatments. Incidence of hollow heart and heat necrosis increased in Atlantic in treatments that tended to have larger tubers. Economic analyses of data suggest that growers can significantly increase profit/hectare by optimizing spacing and populations with Atlantic and seedpiece populations in Superior.

Potato production on wide beds: Impact on yield and selected soil physical characteristics

Planting three rows of potatoes in a bed the width of two conventional rows offers an easily managed way to increase seed piece populations, with the potential of increasing tuber yield and enhancing tuber quality. A wide bed production system (3 rows of potatoes planted on a 1.9 m flat-topped raised bed) was compared to a conventional-ridged system (1 row of potatoes in sharply sloped ridges on 96 cm centers) in 1996 and 1997 on a Norfolk sandy loam soil and a Portsmouth fine sandy loam soil in eastern North Carolina. Potato plant stands, leaf area index at approximately 9 WAP, yield, and quality were measured. Soil temperature, soil moisture, and cone index, as a measure of soil penetration resistance, were also measured, wide beds were more moist than conventional ridges early in the season. Cone index was greater throughout the root profile in wide beds in two of three tests. The row on the west side of an individual wide bed was most similar to conventional ridges in daily soil temperature fluctuations between minimum and maximum temperatures, and had greater fluctuations than the middle and eastern rows of the wide bed. Total yield and yield of grade A potatoes were not significantly different between wide beds and conventional ridges at either site. At one site, yield of grade B potatoes was significantly less in the wide bed; among the three rows in the wide bed, the eastern row had significantly lower yield of grade B potatoes. Conventional ridges had a higher percent of green grade A potatoes than the wide beds in one of three trials. Under North Carolina conditions, changing production systems would be unadvisable for most growers because wide beds do not increase yield enough to justify spending the money for more seed and to change equipment.

Cover Crop Management Affects Weeds And Yield in Organically Managed Sweetpotato Systems

A 3-yr field experiment was initiated in 2001 to evaluate weed suppression and sweetpotato productivity in three organic sweetpotato production systems. Organic systems were (1) compost and no cover crop with tillage (Org-NC), (2) compost and a cover crop mixture of hairy vetch and rye incorporated before transplanting (Org-CI), and (3) compost and the same cover crop mixture with reduced tillage (Org-RT). A conventional system with tillage and chemical controls (Conv) was included for comparison. Suppression of monocot and dicot weed density and biomass was similar between Org-NC and Org-CI each year, and were frequently similar to Conv. Org-RT was as effective as Org-NC in controlling dicot weed density and biomass each year, but did not suppress monocot weeds. At sweetpotato harvest, an increase in cover crop surface residue biomass in Org-RT was associated with a decrease in cumulative total weed density (R2 = 0.43, P = 0.0001); however, the amount of that residue was insufficient to suppress late-emerging monocot weeds. Total sweetpotato yield in Org-RT was at least 45% lower than other systems in 2002 and was most likely due to an increase in monocot weed density and biomass concurrent with a decrease in sweetpotato vine biomass. Total sweetpotato yield was similar among all systems in 2001 and 2004; the exception was lowest yields obtained in the Org-RT system in 2002. Organically managed sweetpotato with or without an incorporated cover crop produced sweetpotato yields equal to conventionally managed systems despite difficulties controlling weeds that emerged later in the season. Nomenclature: EPTC; napropamide; hairy vetch, Vicia villosa Roth; rye, Secale cereale L. ‘Wrens Abruzzi’; sweetpotato, Ipomoea batatas (L.) Lam. ‘Beauregard’.

A technique for assessing environmental impact risks of agricultural systems.

Conventional agriculture often aims to achieve high returns without allowing for sustainable natural resource management. To prevent environmental degradation agricultural systems must be assessed and environmental standards need to be developed. This study used a multi-factor approach to assess the potential environmental impact risk of six diverse systems: five production systems and a successional system or abandoned agronomic field. Assessment factors were soil quality status, amount of pesticide and fertilizer applied, and tillage intensity. The assessment identified the certified organic system and the BMP-conventional tillage system as high-risk systems mostly because fertilizer and tillage use were highest. Conversely, the BMP-no tillage and the crop-animal integrated system were characterized as low-risk mainly because of reduced tillage. The paper discusses assessment strengths and weaknesses, ways to improve indicators used, and the need for additional indicators. We concluded that with further development the technique will become a resourceful tool to promote agricultural sustainability and environmental stewardship, and assist policy making processes. Subject Matter

A survey of cover crop practices and perceptions of sustainable farmers in North Carolina and the surrounding region

The environmental benefits of cover cropping are widely recognized but there is a general consensus that adoption levels are still quite low among US farmers. A survey was developed and distributed to more than 200 farmers engaged in two sustainable farming organizations in NC and the surrounding region to determine their level of utilization, current practices and perceptions related to cover cropping. The majority of farms surveyed had diverse crop production, production areas <8 ha, and total gross farm incomes <US