The ecological principles that define the competitive and complementary interactions among trees, crops, and fauna in agroforestry systems have received considerable research attention during the recent past. These principles have not yet, however, been adequately integrated and synthesized into an operational approach. This paper reviews the ecological and ecophysiological bases for interspecific interactions based on data from site-specific research and demonstration trials from temperate agroforestry systems, primarily from temperate North America. The review shows that information on ecological interactions in several temperate agroforestry systems is inadequate. It is recommended that the future research should focus on exploring new species and systems that have received little attention in the past. Priority research areas should include cultural practices and system designs to minimize interspecific competition and maximize environmental benefits such as improved water quality. Potential for genetic modification of components to increase productivity and reduce competition also needs to be explored. Process-oriented models may be used increasingly to predict resource-allocation patterns and possible benefits for a suite of site and species combinations.

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Interspecific interactions in temperate agroforestry

http://orton.catie.ac.cr/repdoc/A11572i/A11572i.pdf

Carbon sequestration in tropical and temperate agroforestry systems: a review with examples from Costa Rica and southern Canada

Negative plant-soil feedbacks play an important role in soil sickness, which is one of the factors limiting the sustainable development of intensive agriculture. Various factors, such as the buildup of pests in the soil, disorder in physico-chemical soil properties, autotoxicity, and other unknown factors may contribute to soil sickness. A range of autotoxins have been identified, and these exhibit their allelopathic potential by influencing cell division, water and ion uptake, dark respiration, ATP synthesis, redox homeostasis, gene expression, and defense responses. Meanwhile, there are great interspecific and intraspecific differences in the uptake and accumulation of autotoxins, which contribute to the specific differences in growth in response to different autotoxins. Importantly, the autotoxins also influence soil microbes and vice versa, leading to an increased or decreased degree of soil sickness. In many cases, autotoxins may enhance soilborne diseases by predisposing the roots to infection by soilborne pathogens through a direct biochemical and physiological effect. Some approaches, such as screening for low autotoxic potential and disease-resistant genotypes, proper rotation and intercropping, proper soil and plant residue management, adoption of resistant plant species as rootstocks, introduction of beneficial microbes, physical removal of phytotoxins, and soil sterilization, are proposed. We discuss the challenges that we are facing and possible approaches to these.

https://www.springer.com/cda/content/document/cda_downloaddocument/Plant-Soil+Feedbacks+and+Soil+Sickness.pdf?SGWID=0-0-45-1382607-0

Plant-soil feedbacks and soil sickness: from mechanisms to application in agriculture.

In this study, effects of juglone and decomposed walnut leaf juice on muskmelon (Cucumis melo cv. Galia) and cucumber (Cucumis sativus cv. Beith Alpha) seed germination percentage and postgermination seedling growth were investigated. Decomposition was carried out by keeping the leaves in distilled water. Muskmelon and cucumber seeds were germinated in Petri dishes at 25°C. Seed germination, seedling elongation and weights were determined at day 10. No significant effect of juglone and decomposed walnut leaf juice on muskmelon seed germination percentage was observed. However, germination of cucumber seed was inhibited significantly. It was found that while both the dry weight root and stems elongation of muskmelon and cucumber seedlings were affected negatively by juglone and undiluted decomposed walnut leaf juices. The negative effect decreased as dilution ratios of decomposed leaf juice increased.

/pdf/allelopathic-effects-of-juglone-and-decomposed-walnut-leaf-5muivhhjfu.pdf

Allelopathic effects of Juglone and decomposed walnut leaf juice on muskmelon and cucumber seed germination and seedling growth

Small farmers in the high Andes (> 2500 m) of Bolivia, Ecuador, and Peru face increasing threats to their livelihoods due to land degradation, climate change, and overall decreases in agricultural productivity. The fragile nature of these agroecosystems and limited capacity of resource-poor farmers in the region to adopt the large-scale use of conventional fertilizer and pest control technologies suggest the need for agroecological intensification to restore soil functioning and ensure long-term sustainability in these systems. This review addresses soil fertility decline from a management perspective and considers six basic approaches to enhance nutrient cycling, crop nutrient acquisition, and long-term productivity. A mass balance approach first defines basic boundaries for nutrient cycling and suggests that erosion control and identification of alternative nutrient sources (e.g., peri-urban wastes, rock phosphate) are critical for reversing negative nutrient budgets. Meanwhile, short-term nutrient dynamics could benefit greatly from improved management of organic residues in combination with low-level inorganic fertilizer applications. There is also a need for greater understanding of soil physiochemical properties throughout much of the Andes and the impacts of management. Similarly, soil biological functioning is critical for successful agroecological intensification and there is great potential for both inoculative and management strategies to promote beneficial soil communities. Crop breeding for smallholder environments should complement strategies of agroecological intensification, taking advantage of high regional agrobiodiversity and experience from stress breeding programs in other regions. Finally, we suggest several means by which the spatial and temporal organization of farms may be improved to enhance overall agroecosystem function.

Pathways to Agroecological Intensification of Soil Fertility Management by Smallholder Farmers in the Andean Highlands

Juglone (5-hydroxy-1,4-naphthoquinone), a chemical substance produced by black walnut (Juglans nigra L.), inhibits the growth and existence of some beneficial soil microorganisms, especially Frankia spp. isolate ArI3 and Rhizobium japonicum. However, no studies to date have reported on the effect of juglone on soil ammonification and nitrification. A field study and laboratory incubation study to investigate this were conducted. In the field, in situ soil ammonification and nitrification were measured within and outside of a 60-year-old black walnut plantation and a eight-year-old poplar (Populus spp. clone DN 177) plantation. In the lab, soil (Sandy Fox Loam), collected in the absence of black walnut trees, was incubated for periods of one to six weeks in the presence of varying concentrations of juglone. In the field, peak summer mean nitrate accumulation rates in soils within the black walnut and poplar plantation were 163 and 95 μg 100 g-1 dry soil day-1 respectively and in soils outside the plantations, 104 (black walnut) and 78 (poplar) μg 100 g-1 dry soil day-1 respectively. No accumulation of ammonium at the end of the incubation period was noted. Therefore, no inhibition effect of juglone on nitrification in the field was observed, and laboratory incubation results confirmed the results of the field study. Results from these studies should address concerns about nitrification inhibition under walnut based intercropping systems.

Juglone (5-hydroxy-1,4 napthoquinone) and soil nitrogen transformation interactions under a walnut plantation in southern Ontario, Canada

Severe environmental problems encountered in the highlands of Bolivia may be remedied through the adoption of agroforestry systems, never before studied adequately in this region. As a first step, seven tree species were tested for growth, survival and health at two elevations in the Bolivian altiplano. Species responded variably with Buddleja coriacea Remy., Pinus radiata D. Don. and Eucalyptus globulus Labill. (at the higher elevation) and E. globulus, Baccharis spp., Robinia pseudoacacia L. and B. coriacea (at the lower elevation), displaying high survival, growth and health. In a related greenhouse study, grain yields of wheat planted in soils amended with incorporated foliage of B. coriacea, P. radiata and E. globulus increased three-fold (0.3 g·plant−1 to >1.0 g·plant−1) over grain yields in unamended soils (B. coriacea > P. radiata = E. globulus). Grain nitrogen (mg·plant−1) increased equally in soils amended with P. radiata and B. coriacea foliage (18 mg N⋅plant−1 to 20 mg·plant−1) but decreased in soils amended with foliage of E. globulus (18 g·plant−1 to 9 g·plant−1).

Agroforestry in the Bolivian Altiplano: evaluation of tree species and greenhouse growth of wheat on soils treated with tree leaves

Timing the application of organic residues and therefore the release of nutrients during decomposition may be critical to the growing crop in tropical alleycropping agroforestry systems. Field experiments were carried out in Turrialba, Costa Rica, to determine differences in Erythrina poeppigiana (Walp.) O.F. Cook leaf decomposition in 3, 9 and 18-year alleycropped agroforestry systems. Treatments consisted of mulch-only, and mulch plus Arachis pintoi Krapov. and W. Gregory var. CIAT 18347 in 3 and 9-year old alleycrops under no-till cultivation. The 18-year old site consisted of treatments with mulch-only and mulch plus chicken manure under disk plow cultivation. Litterbags, filled with E. poeppigiana leaves from 3, 9 and 18-year old trees, were placed on the soil surface and collected over a period of 84 days. Results showed no significant differences in the amount of plant residues remaining after 84 days in the 3-, 9-, and 18-year-old systems, or between the manure and mulch-only treatments. Comparing mulch-only treatments, leaves in the 18-year old system decomposed most rapidly which may be due to disk-plow cultivation practices where litterbags were in direct contact with the soil as opposed to the no-till system in the younger alleycrops.

R. P. Voroney

Papers

Juglone (5-hydroxy-1,4 napthoquinone) and soil nitrogen transformation interactions under a walnut plantation in southern Ontario, Canada

Agroforestry in the Bolivian Altiplano: evaluation of tree species and greenhouse growth of wheat on soils treated with tree leaves

Decomposition of Erythrina poeppigiana leaves in 3-, 9-, and 18-year-old alleycropping systems in Costa Rica