Search Results

You are looking at 1 - 7 of 7 items for

  • Author or Editor: S.S. Snapp x
Clear All Modify Search
Author:

Extension services around the globe face increasingly limited financial support, yet rural populations require services, training and access to information. In sub-Saharan African countries the demands are particularly severe. Farmer to extension staff ratios are generally over 2000 to 1 and resource constraints are severe, which greatly restricts outreach efforts. Examples are presented of recent innovations from the southern Africa country of Malawi. These include collaboration across private and public institutions. Some extension agents have shifted from a transferring technology mode to a catalytic role where agents help link up diverse stakeholders, from farmers and researchers to potential buyers and input suppliers. Extension has helped farmers respond to new market opportunities, including a food colorant, the paprika pepper (Capsicum annuum), and a multi-use grain and vegetable, pigeon pea (Cajanus cajan). Product quality is critical for these markets and industry organizations have invested in training that involves government extension staff, private crop advisors and farmers. A collaborative team approach across industry, nongovernmental organizations and government services has facilitated farmer access to inputs, new cultivars and training in improved crop management and post-harvest techniques. Many challenges remain, such as outreach to farmers located far from infrastructure and those with limited formal education or no experience with entrepreneurship. Extension must continue to reinvent itself to reach all farmers.

Full access
Authors: and

Roots respond first to edaphic stresses, yet little is known about root response to stress in mature, soil-grown plants. We investigated the effects of salinity and phytophthora root rot on root growth and senescence in tomato (Lycopersicon esculentum Mill.). Using minirhizotron- and rhizotron-based methodologies, we quantified intraspecific differences in root-system response to salinity and inoculation. Genotype susceptibility to salt-induced disease was related to root vulnerability to salt. `UC82B' was vulnerable to infection by Phytophthora parasitica when subjected to salt stress and produced thinner roots and ≈50% higher root-senescence rates compared to the phytophthora root rot-resistant `CX8303'. Root growth at the peripheral regions of the `CX8303' root system was inhibited by salinity, but otherwise root dynamics were not affected by salinity or inoculation. Overall, roots from the central root system and roots from the periphery responded differently to salt stress. Monitoring the diameters of new initiated roots indicated the vulnerability of a stressed root system to disease and early senescence.

Free access

The appearance of a fruit quality defect, shoulder check in fresh-market tomatoes (Lycopersicon esculentum Mill.), has devastated the Michigan industry, and caused sporadic concern elsewhere. The defect appears as a surface roughness that occurs primarily on the shoulder area of the fruit. The fruit appearance is damaged and storability is severely compromised. Microscopic inspection reveals that the surface roughness consists of many microscopic cracks that occur in parallel lines. Our objectives were to describe this defect and evaluate the role of weather conditions and fruit surface moisture in inducing it. Field experiments were conducted in 2001 and 2002 in Southwest Michigan, using the industry standard cultivar Mountain Spring and recommended practices for irrigated, staked fresh market production. The effects of fruit surface wetness and nutrition on quality were evaluated by comparing responses to a plastic rain shelter; Surround WP kaolin spray (to enhance surface wetness); a foliar spray of calcium (Ca at 2 g·L-1), boron (B at 300 mg·L-1), Ca plus B, water alone; and no treatment. A complementary greenhouse experiment investigated the effects of low and high rates of foliar sprays. A very consistent association was found between defect incidence and precipitation events that followed periods of hot, dry weather during rapid fruit expansion. Fruit quality was highest and incidence of defects least in fruit produced under plastic rain covers, with an average marketable yield of 62,270 vs. 44,340 kg·ha-1 for the control. A 28% reduction in defects was consistently associated with Ca + B sprays across harvests and years. In contrast, 18% more fruit had shoulder check defect with kaolin spray, a consistent increase in defect across years compared to control fruit. Greenhouse and field studies gave markedly similar results, except for a water spray control. Incidence of defect was consistently low with the highest rate of B foliar spray.

Free access
Authors: and

Growers lack practical decision aides that accurately predict nitrogen (N) credits for organic sources to adjust fertilizer rates. The simulation model, DSSAT, was used to predict N supply in relationship to N demand in irrigated potatoes (Solanum tuberosum). Tuber yield and soil inorganic N levels were substantially higher in the simulations than in field experiment observations, indicating the need for model improvement. DSSAT was successful at predicting relative mineralization rates and potato N uptake for different organic and inorganic N source combinations. Interestingly, both simulation and field experiment observations indicated that combining a high quality organic manure at 5000 lb/acre (5604.2 kg·ha-1), total applied N 250 lb/acre (280.2 kg·ha-1), and a fertilizer source of N 160 lb/acre (179.3 kg·ha-1) markedly increased yields and lowered leaching potential. Simulated tuber yield for the combined treatment was 660 cwt/acre (74.0 t·ha-1) with 48 lb/acre (53.8 kg·ha-1) inorganic-N in the profile at harvest, whereas the highest simulated N fertilizer response was to 235 lb/acre (263.4 kg.·ha-1), which produced 610 cwt/acre (68.4 t·ha-1) with 77 lb/acre (86.3 kg·ha-1) inorganic-N in the profile at harvest. The synchrony of N release and uptake for combined manure and fertilizer treatments may explain the efficient N uptake observed. Common soil types and weather scenarios in Michigan were simulated and indigenous soil N mineralization was predicted to be 6 lb/acre (6.7 kg·ha-1) inorganic-N in the topsoil at planting, similar to observed levels. The increasing aeration associated with a sandy versus a sandy loam soil only slightly increased the predicted rate of mineralization from organic inputs. Simulated soil inorganic N levels with different organic inputs was modestly increased in a warm spring [4.5 °F (2.50 °C) over normal temperatures] compared to a cool spring (-4.5 °F less than normal temperatures). For Michigan irrigated potato systems, DSSAT simulations indicate that the most important factor determining inorganic N supply will be the quality and quantity of organic inputs, not environmental conditions.

Full access

Separate evaluation of main and external roots was critical to understanding results from a study on phosphorus (P) efficiency in common bean. A subsection of the root system, including both main roots and external roots, was compartmentalized and subjected to low P conditions. The rest of the root system was maintained at either low or high P-nutritional status. P distribution at the mid-pod fill stage was determined for root components (main and external roots) and shoot components (leaves, stems, pods). A 50% inhibition in main root growth and moderate reductions in diameters of both root types were found in low P plants compared to high P plants. Marked reduction in main root growth, coupled with a limited reduction in external root growth and thinner roots, allowed low P plants to reduce biomass and P investment in compartments by 54 and 42%. Yet root exploration of the compartment, in terms of root length per soil volume, was similar for both low and high P plants. Further, P removal from compartments was similar for roots of low P plants and high P plants. Taken together, the data suggest efficiency of P acquisition in P-stressed common bean is enhanced by selective inhibition of main root growth and continued growth of external roots.

Free access

Fusarium root rot is a major limiting factor in snap bean (Phaseolus vulgaris L.) production. The level of genetic resistance in commercial bean cultivars is minimal and disease is frequently exacerbated by environmental factors. We investigated the contribution of vigorous, adventitious roots to enhancing root rot tolerance in snap bean. Seedling root system architecture was evaluated in 17 recombinant inbred lines (RILs) from a cross of a resistant snap bean line (FR266) and a susceptible dry bean cultivar (Montcalm). The RILs varied in tolerance to Fusarium root rot. Although overall length and branching density (as measured by fractal dimension and meristem numbers) of root systems were not related to root rot resistance, the lateral root number at the root: shoot interface was positively correlated with genotype tolerance (R 2 = 0.6*). Root diameter was also positively correlated with tolerance; this is consistent with the hypothesis that larger adventitious and basal roots are beneficial under disease stress. A field-based study of commercial snap bean cultivars compared raised and flat-bed systems of production, in a soil inoculated with Fusarium solani f. sp. phaseoli. Substantially greater yields (40% to 90%) were observed in raised beds. Root vigor was relatively high (root length density >0.2 cm·cm−3) and root rot scores were lower with raised than with flat-beds, in 2001, but not in 2000. Overall, this is suggestive that integrated crop management practices can improve lateral root vigor and reduce root rot severity.

Free access