R. L. Perry

Arbuscular mycorrhizal fungi induced alteration to root longevity of poplar

Root longevity is an important element determining the fluxes of nutrients and carbon within terrestrial ecosystems. The effect of colonisation by an arbuscular mycorrhizal (AM) fungus on root longevity of poplar was determined using a minirhizotron camera to make direct observation of roots in situ in conjunction with image analysis. significant influences of colonisation on the longevity of roots were observed with most colonised roots surviving for a shorter period than non-colonised roots: only 16% of colonised roots survived for longer than 49 days compared to 49% of non-colonised roots. After 21 days approximately 5 times as many colonised as non-colonised roots had died. Possible mechanisms are discussed.

Root distribution of fourVitis cultivars

SummaryRoot distribution of fourVitis cultivars at one location in Texas was asessed using trench profile and soil core sampling methods. Greater differences were obtained among cultivars utilizing the latter method when comparing root dry weights. Surface area of roots extracted from soil samples was estimated using a calcium nitrate slurry dip. This technique was found to be unreliable.Vitis champini cv. Dogridge maintained the greatest above-ground canopy and the most extensive root system. In measuring root numbers and dry weight,V. rotundifolia cv. Noble ranked at or near the bottom withV. vinifera cv. Barbera andV. labruscana cv. Concord being intermediate. Overall schematic root system patterns for each cultivar indicate that Noble is shallow rooted, having more than 35% of the total roots in the 0–15 cm depth. In contrast, ten percent of the total Dogridge roots were found at the 90–105 cm depth.

Soil properties under different orchard floor management systems for organic apple production

Orchard floor management impacts soil conditions and thus tree performance. This research was initiated to investigate the effects of alternative orchard floor management systems compatible with organic production on soil parameters using the “Pacific Gala” apple cultivar (Malus × domestica Borkh.) on three rootstocks of varying vigor. Alfalfa hay mulch, propane flame burner, and Swiss sandwich system (combination of resident vegetation and tilled strips) were compared from 2001 to 2005. These treatments were applied to tree rows which provided different vegetation-free areas. Contrasting additions of organic matter were evaluated for their effect on soil organic matter (SOM), C content, nitrate and ammonium availability, moisture, and soil food web through nematode populations. Laboratory incubations to determine C and N mineralization potentials were performed. During this time period, SOM increased under the mulched soil and slightly less under the Swiss sandwich system (SSS) but in this last case without external inputs. Carbon and N pools were not impacted by flame burning (FL) but were enhanced by alfalfa hay mulch (MU) and to a lesser extent by SSS. Nitrate-N content in soil under MU increased between five and ten times compared to SSS and FL. Total number of nematodes was higher for SSS and MU compared with FL treatment; however, SSS had the most structured soil food web, an important sustainability trait, while MU had the least.

Influence of cherry rootstock on the cold hardiness of twigs of the sweet cherry scion cultivar

Abstract Scion twig tissue of the sweet cherry cultivars ‘Hedelfingen’, ‘Napoleon’ and ‘Gold’ were subjected to cold hardiness evaluations in the late fall (November 21, 1984) and early spring (March 1, 1985) of the same dormant season. ‘Hedelfingen’ and ‘Gold’ were grafted to the rootstocks ‘Colt’ and ‘Mazzard’. At sampling, the twig tissues were stratified statistically as to apical and basal positions on the twig. A comparison of scion tissues grown on the rootstocks in common (‘Mazzard’ and ‘Colt’) showed a scion cultivar hardiness ranking of ‘Gold’ > ‘Hedelfingen’ > ‘Napoleon’. Separate evaluations included two other rootstocks: ‘MxM-39’ for ‘Gold’ and ‘Hedelfingen’, and ‘Mahaleb’ for ‘Napoleon’. Rootstock influence on scion twig tissue showed that ‘Gold’ and ‘Hedelfingen’ produced the following hardiness ranking: ‘MxM-39 > ‘Mazzard’ > ‘Colt. For ‘Napoleon’ the ranking was: ‘Mahaleb’ > ‘Colt’ > ‘Mazzard’. Basal tissues on sampled twigs were more hardy than apical tissues on the dates sampled.

Evaluation of nitrate-nitrogen leaching from lysimeter-grown bearing apple trees

A 2-year investigation was conducted on eight replicate plots located 30 miles east of Lake Michigan on sand to sandy-clay-loam soil, using 1.8-m-deep lysimeters (4.8 m3 of volume), consisting of an undisturbed monolith excavated from the soil and containing a bearing (2- to 3-year-old) apple tree each. The aims of this research were to study the leaching rate and migration time of nitrate-N (NO3−-N) through the soil profile and to assess the suitability of soil suction tube (SST) water samples to predict the NO3−-N leaching rate. The NO3−-N concentration in the water collected by the lysimeters ranged from less than 10 mg L−1 (in late summer) to more than 40 mg L−1 (in winter). We calculated that NO3−-N lost via leaching in a year amounts up to 141 kg ha−1, with the most potential for groundwater pollution occurring during the cold and wet season. The application of labeled N ammonium nitrate as fertilizer increased the concentration of NO3−-N in the solution collected by SST. Labeled N was found at the bottom of lysimeters 3 months after its application, leaching through the soil profile at a speed of 2 cm day−1, so that the NO3−-N concentration of SST was correlated significantly with NO3−-N concentration of lysimeters only when the time of movement was considered. The application of fertilizer did not increase the amount of NO3−-N collected by lysimeters, meaning that the NO3−-N leaching rate is mostly the result of the breakdown of soil organic matter.