Applications of black walnut husks can improve orchardgrass and red clover yields in silvopasture and alley cropping plantings

Black walnut (Juglans nigra L.) produces both valuable lumber and a nut crop. Because of this, it is an important tree for agroforestry plantings in the Midwest USA. However, during processing of the nut crop, the outer tissue of the nut (husks) accumulates in great quantities. Applying this material to pastures is a possible method of disposal. However, black walnut has been implicated in allelopathic interactions with numerous plant species and may inhibit the growth of pasture species. Greenhouse and field studies and a chemical analysis of the husks were conducted to determine the effects of applying walnut husks to orchardgrass (Dactylis glomerata L.) or red clover (Trifolium pratense L.) pastures. Applying husks at rates up to 68 Mg ha⁻¹ to pot-grown orchardgrass resulted in root and shoot yields that were greater than in pots receiving no husks. Field studies indicated that orchardgrass and red clover benefited from the application of husks. For orchardgrass, significant increases in growth occurred when husks were applied at a rate of 34 Mg ha⁻¹ while red clover responded to rates up to 68 Mg ha⁻¹. A chemical analysis of husks indicated that significant quantities of N and K were present in walnut husks. A whole effluent toxicity test (WETT) indicates that runoff from walnut husk-treated pastures, at the rates used in this study, would not adversely affect aquatic organisms.     

Nitrogen fertilization and aspects of fruit yield in a Missouri black walnut alley cropping practice

Increasing nut production through cultural practices is important to landowners for maximizing economic gain from agroforestry plantings. This project studied the effects of applying low rates of nitrogen (N) fertilizer during either the spring or late summer, on pistillate flowers formed, fruits retained, and fruit quality (percentage kernel) in black walnut (Juglans nigra L.) grown under alley cropping management. Treatments consisted of two forms of nitrogen fertilizers (NH₄NO₃ and NaNO₃) applied in mid-April, or mid-August of 1995 and 1996, and a nonfertilized control group. Pistillate flowers counted in May, 1996, showed that fertilized trees, regardless of timing or form of N applied, produced from 2.3 to 3.4 times the number of pistillate flowers as unfertilized control trees. Through the season, the fertilized trees had greater fruit retention, and ended with 2.9 to 4.8 times more walnuts (on a whole tree basis) than nonfertilized control trees. In addition, all fertilizer treatments resulted in increased nut yields from 1995 to 1996, while unfertilized control tree yields decreased approximately 70%. Summer application of fertilizer showed the greatest benefit to kernel weight. Average kernel weights of nuts from the summer-fertilized trees increased from 1995 to 1996, while kernel weight averages from spring-fertilized and nonfertilized trees remained unchanged or decreased. This revised version was published online in June 2006 with corrections to the Cover Date.     

Soil carbon dynamics and residue stabilization in a Costa Rican and southern Canadian alley cropping system

Agroforestry systems can play a major role in the sequestration of carbon (C) because of their higher input of organic material to the soil compared to sole crop agroecosystems. This study quantified C input in a 19-year old tropical alley cropping system with E. poeppigiana (Walp.) O.F Cook in Costa Rica and in a 13-year old hybrid poplar (Populus deltoides × nigra DN-177) alley cropping system in southern Canada. Changes in the level of the soil organic carbon (SOC) pool, residue decomposition rate, residue stabilization efficiency, and the annual rate of accumulation of SOC were also quantified in both systems. Carbon input from tree prunings in Costa Rica was 401 g C m⁻² y⁻¹ compared to 117 g C m⁻² y⁻¹ from litterfall at the Canadian site. In southern Canada, crop residue input from maize (Zea mays L.) was 212 g C m⁻² y⁻¹, 83 g C m⁻² y⁻¹ from soybeans (Glycine max L.) and 125 g C m⁻² y⁻¹ for wheat (Triticum aestivum L.), and was not significantly different (p < 0.05) from the sole crop. The average yearly C input from crop residues in Costa Rica was significantly greater (p < 0.05) in the alley crop for maize (134 g C m⁻² y⁻¹) and Phaseolus vulgaris L. bean crops (35 g C m⁻² y⁻¹) compared to the sole crop. The SOC pool was significantly greater (p < 0.05) in the Costa Rican alley crop (9536 g m⁻²) compared to its respective sole crop (6143 g m⁻²) to a 20 cm depth, but no such difference was found for the southern Canadian system. Residue stabilization, defined as the efficiency of the stabilization of added residue (crop residues, tree prunings, litterfall) that is added to the soil C pool, is more efficient in southern Canada (31%) compared to the alley cropping system in Costa Rica (40%). This coincides with a lower organic matter decomposition rate (0.03 y⁻¹) to a 20 cm depth in Canada compared to the Costa Rican system (0.06 y⁻¹). However, the average annual accumulation rate of SOC is greater in Costa Rica (179 g m⁻² y⁻¹) and is likely related to the greater input of organic material derived from tree prunings, compared to that in southern Canada (30 g m⁻² y⁻¹) to a 20 cm depth.     

The potential of alley cropping in improvement of cultivation systems in the high rainfall areas of Zambia I. Chitemene and Fundikila

Three trials investigating the potential of alley cropping to improve the traditional systems of cultivation, chitemene and fundikila, in the Northern Province of Zambia are described. Flemingia congesta, Tephrosia vogelii, and Sesbania sesban, were grown in association with finger millet, groundnut, cowpea, and maize in various traditional cropping sequences. The indigenous species Tephrosia vogelii and Sesbania sesban were not able to withstand repeated pruning and the long following dry season, and were replaced with Calliandra calothyrsus, and Cassia spectabilis.Over a four year period, there was no benefit by alley cropping with any of the tree species on crop yields, and yields in alley crop treatments even dropped significantly below the control treatments in the fourth year, casting doubt on the potential of alley cropping for sustainable production. There was also no consistent effect on soil chemical characteristics in any of the trials. It was suggested that this lack of beneficial response to alley cropping was due to low tree biomass production low quality of prunings, and an inappropriate cropping sequence. There was no evidence that alley cropping contributed to enhanced nutrient recycling, despite substantial localised pools of soil nutrients, particularly in the chitemene, with which recycling could potentially occur.     

Stepwise approach to alley cropping technology development and transfer in the forest zone of Cameroon

Two projects on alley cropping research and development have been implemented in the Forest zone of Cameroon (FZC) since 1988. Their goal was to identify the main agricultural constraints in the FZC and to introduce alley cropping in the farming systems to improve soil fertility and crop yields. The first step in the implementation process was the participatory surveys which revealed that (a) the main agricultural constraint in the FZC is low soil fertility; (b) alley cropping is an agroforestry technology which may solve the problem; (c) alley cropping should be first targetted to farmers who own inherited or purchased lands. The second step was the on-station tree screening activity from which Leucaena leucocephala, Gliricidia sepium, Calliandra calothyrsus and Paraserianthes falcataria were identified as promising tree species. The third activity was to test alley cropping with three promising tree species (Leucaena, Gliricidia and Calliandra) on farmers' fields. Results from the first year testing on farmers' fields showed that: (1) the direct seeding method used was ineffective: seedling emergence rate was 45% for Leucaena and 52% for Gliricidia; (2) Cassava suppressed the growth of Leucaena and Gliricidia by 57 and 45%, respectively; (3) three-month-old Calliandra seedlings planted 1 m away from cassava plants had 96% survival rate. Based on these third step findings, all new farms were established with Calliandra seedlings using maize as a test-crop in the year of establishment and the subsequent year. After two years of cropping, maize grain yield in alley plots was 52% higher than maize grown on no-tree plots. In 1993, 52 farmers who had witnessed the alley farm maize growth in 1992 requested to join the project. This sudden interest of farmers to start their own alley farms was considered as a positive sign for adoption and therefore a success in alley cropping (AC) introduction in the zone.     

The potential of alley cropping im improvement of cultivation systems in the high rainfall areas of Zambia II. Maize production

Theee trials to evaluat the potential of alley cropping in maize production on the low fertility, acidic soils in Northern Zambia are described. Leucaena leucocephala, Gliricidia sepium, Sesbania sesban, Albizia falcataria, Fleminga congesta, and Cassia spectabilis, were grown in alley crops with hybrid maize and soybean. All trials received recommended rates of P and K fertiliser; N fertiliser was applied at three rates as a subplot treatment. One trial received lime before establishment.Only in the limed trial was there a significant improvement in maize yields through alley cropping; when no N fertiliser was applied, incorporation of Leucaena leucocephala prunings resulted in an increase of up to 95% in yields, with a smaller improvement being produced by Flemingia congesta. There was a significant correlation between the quantity of prunings biomass applied and the proportional increase in maize yields over the control treatment. It is suggested that the lack of effect of most of the tree species on crop yields was due to low biomass production.An economic analysis showed that alley cropping with limed Leucaena was only profitable when fertiliser costs were high in relation to maize prices. However, lime is both expensive and difficult to obtain and transport for most small scale farmers in the region, and is therefore not a practical recommendation. It is suggested that future alley cropping research should focus on screening a wider range of tree species, including other species of Leucaena, for acid tolerance and higher biomass production.     

Competition for light between hedgerows and maize in an alley cropping system in Hawaii, USA

Successful agroforestry systems depend on minimizing tree-cropcompetition. In this study, field experiments and a simulation model were usedto distinguish between tree-crop competition for light and belowgroundcompetition in an alley cropping system. Maize (Zea maysL.) was harvested periodically in three treatments: between vertical barriers ofshade cloth, hedgerows of Flemingia macrophylla (Willd.)Merr., and sole maize. Radiation intercepted by the maize was calculated using asimulation model based on measured values for direct and diffuse light, hedgerowdimensions and leaf area, and solar trajectory. Radiation use efficiency wascalculated as biomass production per unit of intercepted radiation. Maizebiomass and yield in both the alley crop and the shade cloth treatment weregreatest in the center of the alleys. Grain yield between hedgerows was 3.5Mg ha⁻¹ (averaged across the alley), significantlyless than in the shade cloth (7.4 Mg ha⁻¹) or thesole maize (7.7 Mg ha⁻¹) treatments. Lightintercepted by the maize in the alley crop was about half that intercepted bythe maize in the sole crop. The shade cloth intercepted less light than thehedgerows because it did not have an appreciable width. Radiation use efficiencyin the three treatments was 0.75 g mol⁻¹ PAR anddid not differ significantly among treatments. Tree-crop competition wasoverwhelmingly for light. This revised version was published online in June 2006 with corrections to the Cover Date.     

Modelling daily root interactions for water in a tropical shrub and grass alley cropping system

A two-dimensional physically-based model for the daily simulation of root competition for water in an alley cropping system associating Gliricidia sepium with Digitaria decumbens is developed. This paper deals with the impact of root distribution on soil water partitioning. By adapting existing principles of root water uptake modelling for pure crops, the model accounts simultaneously for the sink terms of each species in a defined soil domain. Soil-root water transport functions are solved at the level of discrete volumes of soil; each of them are characterized by the inherent soil physical properties, root length density, soil-root distances, and the calculated sink terms of each species. The above ground boundary conditions, such as transpiration and soil evaporation, were managed by simple equations found from the literature or provided by experimental measurements. Running the model with two contrasting observed root maps, an evaluation was carried out over a 10-day period following a rainfall event. With both root maps, the simulated soil water potential profiles at the row, at 0.75 m and 1.50 m from the row did not differ significantly, and were in good agreement with the measurements. However, although water was not limiting during this period, the simulated cumulative water absorption profiles of G. sepium and D. decumbens contrasted markedly, and matched their observed root distribution. This model, although still under further development, forms the basis for development of an above and below ground coupled model to simulate plant interactions for water in intercrops or agroforestry.This revised version was published online in November 2005 with corrections to the Cover Date.     

Potentials of Millettia thonningii and Pterocarpus santalinoides for alley cropping in humid lowlands of West Africa

This study was conducted to assess the suitability of two fallow species that are indigenous to West Africa, M. thonningii (Schum and Thonn) and P. santalinoides (L'Her), for alley cropping with maize and their effect on soil chemical properties. It was carried out during the rain-fed cropping season at Ibadan, Nigeria and Mbalmayo, Cameroon in 1993 and 1994. Total dry matter of P. santalinoides prunings was higher at the two sites than that of M. thonningii by about 35% to 37%. Maize grain yield in plots supplied with prunings was significantly higher (P > 0.05) than in control (no prunings or fertilizer application) at Ibadan. Grain yield in plots supplied with prunings plus 40 kg ha⁻¹ urea fertilizer gave significantly higher yields than plots supplied with 80 kg N ha⁻¹ urea fertilizer only. At Mbalmayo, there was no significant difference between grain yield in plots supplied with 80 kg N ha⁻¹ and plots supplied with prunings plus 40 kg N ha^-1 urea fertilizer though the latter had higher yields. Grain yield was also higher in the middle rows than in rows adjacent to the hedgerows and these were not significantly different. Weed dry matter was reduced by 27% to 43% when Pterocarpus prunings were applied and 13% to 31% with application of Millettia prunings. Weed flora in both locations changed from grasses to broad leaved. Soil chemical changes at soil depth 0 to 10 cm showed significant increases (pH, C, N, P and Ca) after two cropping seasons in plots supplied with prunings or prunings plus fertilizer than the initial values. At Mbalmayo, K was lower after cropping in treatments than the initial values while at Ibadan, K and Mg were lower except in plots supplied with Pterocarpus prunings only. P. santalinoides and M. thonningii have significant potential for agroforestry in this sub-region. This revised version was published online in June 2006 with corrections to the Cover Date.     

Nitrogen contribution by multipurpose trees to rice and cowpea in an alley cropping system in Sierra Leone

In an alley cropping experiment, a study was carried out on N₂ fixation by Gliricidia sepium, nitrogen (N) accumulation by prunings of Gliricidia, Senna siamea (formerly Cassia siamea) and Gmelina arborea, and the N contribution to associated crops of rice and cowpea.Total N accumulated by the hedgerow trees ranged from 297–524 kg N ha^–1 on average but varied between tree species and depended on the growing season. Gliricidia sepium accumulated 370 kg N ha^–1 on average and more than half of this came from fixation. Senna siamea and Gmelina arborea served as reference trees for estimating N₂ fixation. The estimates of N₂ fixation using Gmelina as a reference gave higher estimates than those using Senna.Although the dry matter and nitrogen yields of prunings from the hedgerow trees were high, their relative nitrogen contribution to the associated crops was generally low ranging from 5 to 29%. Higher crop yields and nitrogen contribution were observed with Gliricidia sepium prunings. The low N contribution from prunings was attributed to the lack of synchronization between the N released from the prunings and the crop's demand for N.     

Comparison of minirhizotron and soil core methods for quantifying root biomass in a temperate alley cropping system

A study was carried out in southern Indiana, USA with the objective of comparing soil core sampling and the minirhizotron technique in quantifying fine root biomass and root distribution patterns in an alley cropping system with black walnut (Juglans nigra L.), northern red oak (Quercus rubra L.) and maize (Zea mays L.). Spatial variation in tree rooting pattern was investigated prior to planting maize. Tree fine root biomass was quantified at distances of 0, 1.1, 2.3, 3.5, and 4.3 m where 0 m represents the tree row and 4.3 m represents the middle of the alley. Root samples were collected to a depth of 90 cm using a hydraulic auger. Maize rooting pattern was determined 65 days after planting to the same depth. Using plexiglass access tubes installed near the actual soil core locations and a minirhizotron camera root images were recorded on a VHS tape. These images were later analyzed using a raster based GIS software (ERDAS-IMAGINE). Regression analysis revealed significant relationships between root surface area measurements from minirhizotron observations and fine root biomass data from soil coring for all species. Predicted fine root biomass data were also in close agreement with actual fine root biomass for all species examined. Maize root biomass was slightly, but not significantly, underestimated by the minirhizotron technique in the top 30 cm soil layer. No significant underestimation or overestimation of root biomass in surface or deeper soil layers was observed for the tree species. The results indicate that minirhizotron can be used in quantifying fine root biomass if site and species specific predictive models can be developed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Economic analysis of cut-and-carry,and alley cropping systems of mulch production for plantains in south-eastern Nigeria

Organic mulch is beneficial to plantain because it maintains soil fertility, prevents erosion and suppresses weeds. Mulch availability is however a major constraint. Mulching in a cut-and-carry system withPennisetum purpureum Schum. (elephant grass) was compared with mulching with the prunings ofAlchornea cordifolia (Schum. & Thonn.),Dactyladenia barteri (Hook. f. ex Oliv.)Engel. (Syn.Acioa barteri),Gmelina arborea (Roxb.) andSenna siamea (Lam.) Irwin & Barneby (Syn.Cassia siamea) in alley cropping systems. Plantain inPennisetum mulch treatment gave the highest bunch yield, but similar net revenues per hectare as theDactyladenia treatment, whileGmelina, Alchornea andSenna treatments produced the lowest incomes. But when the land required to producePennisetum mulch was included in the economic analysis, the net revenue per hectare was negative over three years of cropping. The returns to labour were also much lower for thePennisetum compared to the alley cropping systems. Among the in-situ mulch sources,Gmelina had the highest labour requirement because of the high pruning frequency. In addition, weeding inGmelina, Alchornea andSenna treatments resulted in high labour demand due to the rapid decomposition of the mulch materials leaving the soil bare for weeds to invade.Dactyladenia alley cropping was the most profitable of the five plantain production systems studied.IITA Journal Paper No: 94/004/JA.     

The potential of alley cropping in improvement of cultivation systems in the high rainfall areas of Zambia. III. Effects on soil chemical and physical properties

A detailed study of the soil chemical and physical properties in seven-year-old alley cropping trial containingLeucaena leucocephala andFlemingia congesta in Northern Zambia is described. There was a strong correlation between the maize yield and the total amount of nitrogen applied, both from prunings and fertiliser, suggesting that a major reason for the observed benefit from alley cropping, particularly withLeucaena, was due to an improvement in nitrogen supply.Leucaena produced significantly more biomass, and its leaves had higher concentrations of nitrogen, phosphorous and potassium and lower C/N and C/P ratios than did those ofFlemingia. There was also evidence that the trees had a beneficial effect on other soil chemical properties; under the hedgerows, particularly those ofLeucaena, there were higher levels of organic carbon, Mg, K and ECEC, and pH values were also highest.It is suggested that higher levels of organic carbon in the alley crop treatments were responsible for the improvements observed in soil physical properties. Lower bulk density, lower penetration resistance, and a higher infiltration rate and pore volume fraction were measured in the alley crops, although there was no significant change in the soil water release parameters.A deteriorating effect of constant applications of nitrogen fertiliser on soil fertility was observed; as the level of urea application increased, there were significant decreases in Mg, K and pH, increases in Al and soil acidity, and higher penetrometer resistance. These results highlight the urgent need for further research on biological methods of maintaining soil fertility.     

Defining competition vectors in a temperate alley cropping system in the midwestern USA: 3. Competition for nitrogen and litter decomposition dynamics

An experiment was conducted in an 11-year-old black walnut (Juglans nigra L.), red oak (Quercus rubra L.), maize (Zea mays L.) alley cropping system in the midwestern USA to examine the extent of tree-crop competition for nitrogen and decomposition dynamics of tree leaves and fine roots. A below-ground polyethylene root barrier (1.2 m deep) isolated black walnut roots from maize alleys in half the number of plots providing two treatments viz. barrier and no barrier. The percentage of N derived from fertilizer (%NDF) and fertilizer use efficiency (%UFN) were determined using ¹⁵N enriched fertilizer. Further, maize grain and stover biomass, tree leaf biomass, tissue N concentration, and N content were quantified in both treatments. The barrier treatment resulted in a significantly greater grain (67.3% more) and stover (37.2% more) biomass than the no barrier treatment. The %NDF in both grain and stover was higher in the no barrier treatment as a result of competition from tree roots for water and mineralized N in soil. Maize plants growing in the no barrier treatment had a lower %UFN than those in the barrier treatment due to their smaller size and inability to take up fertilizer. Analysis of tree leaf and fine root decomposition patterns revealed faster release of N (39% over 15 days for black walnut and 17.7% for red oak) and P (30% over 15 days for both species) from roots compared to the leaves of both species. Following an early release of P (11.3% over 45 days), red oak leaves exhibited significant immobilization for the rest of the incubation period. The data indicate that competition for N from fertilizer is minimal since nutrient acquisition is not simultaneous among black walnut and maize. However, competition for mineralized N in soil can exist between black walnut and maize depending on water availability and competition. Tree leaves and fine roots can enhance soil nutrient pools through the addition of soil carbon and nutrients. Tree fine roots seem to play a more significant role in nutrient cycling within the alley cropping system because of their faster release of both N and P as compared to leaves. Selection of tree species and their phenology will impact the magnitude and rate of nutrient cycling.This revised version was published online in November 2005 with corrections to the Cover Date.     

The effects of alley cropping withLeucaena leucocephala and of different management practices on the productivity of maize and soil chemical properties in lowland coastal Kenya

The effects of leucaena hedgerows, mulching with leucaena foliage (0,50 and 100% of harvested foliage), cowpea intercropping and adition of dairy cattle slurry (55 t ha^–1 per maize crop) on the yield of maize from a sandy soil were assessed. The four-year results from five maize crops are reported.Except in the first year, yields of maize grain and stover were significantly reduced by 30% in the presence of leucaena hedgerows. Use of leucaena mulch eliminated this effect; application of all the harvested leucaena mulch (100%) increased the total maize grain yield of the five crops by 44% over sole maize. Hedgerow and mulching management required an additional 36 mandays labour ha^–1 which was more than compensated by the increased maize yields. Furthermore leucaena hedgerows substantially depressed the growth of weeds between cropping seasons.Intercropping with cowpea significantly depressed yields of maize grain and stover when both crops were sown together, but not in later seasons when cowpea was sown four weeks after the maize. Application of slurry increased the total yields of maize grain and stover by 35 and 37%, respectively. The grain yield of maize in leucaena hedgerow treatments fertilized with slurry did not respond to application of more than 50% of leucaena foliage, which suggested that half of the foliage could be spared for feeding to livestock. The cumulative yield of maize grain from the highest yielding organic system was 85% of the yield from the fertilizer treatment.The study, which is continuing, demonstrates that large increases in agricultural productivity are possible through the intercropping of maize with woody forage and grain legumes and the integration of dairy cattle production into the system. It thus shows the importance of exploiting crop/livestock interactions.     

The potential of resynthesized lines to provide resistance traits against rape stem weevil in oilseed rape

The rape stem weevil, Ceutorhynchus napi Gyll., is a serious pest of winter oilseed rape (Brassica napus L.) crops in Europe that causes stem distortion, severe disruption of stem growth, and significant yield loss. No resistance has been identified in current B. napus breeding material. Resynthesized lines of oilseed rape can be used to introduce genetic material from the parent species Brassica oleracea L. and B. rapa L. The susceptibility to C. napi of five resynthesized lines and three cultivars of oilseed rape was compared in a multi-choice field plot experiment. Morphological stem traits and stem levels of glucosinolates, carbon, and nitrogen were assessed as potential mediators of resistance. Eggs and larvae of C. napi in stems were counted weekly from the beginning of oviposition to larval maturation and stem pith degeneration in response to oviposition was assessed. Egg counts per stem were negatively dependent on stem length and positively dependent on the levels of five glucosinolates, glucobrassicanapin, glucoalyssin, glucobrassicin, neoglucobrassicin, and gluconasturtiin. The resynthesized line S30 was significantly more resistant to C. napi than the commercial cultivar Sollux, having fewer eggs and larvae. This resistance appeared to be largely antixenotic, due to the combination of a long stem and a paucity of the five key glucosinolates. We propose that resynthesized lines such as S30 should be used to introduce genes determining traits such as long stem length and glucosinolate profile into breeding programs to enhance resistance against C. napi in oilseed rape.     

Soil organic carbon stock in relation to aggregate size and stability under tree-based cropping systems in Typic Ustochrepts

The growing of tree crops along with the field crops is a common practice in foothills of lower Himalayas with the twin objective of checking soil erosion by water and covering the risk of crop failure due to frequently occurring droughts. A study was conducted to evaluate dry and water stable aggregates for their soil organic carbon (SOC) stocks under different tree-based cropping systems. The treatments consisted of three cropping systems viz. maize-wheat (sole crop), agroforestry and agrohorticulture (tree-based) in the similar soil texture and in 6 year old plantations. The soil samples were obtained from different layers (0–15, 15–30, 30–60, 60–90 and 90–120 cm) and analyzed for SOC. The undisturbed aggregate samples (as big clods) were collected from 0–15 and 15–30 cm soil layer for dry and wet aggregate stability. The data so obtained was analyzed by using CRD factorial deigns at LSD (P ≤ 0.05). The SOC concentration decreased with soil depth, the decrease was higher (89.6%) in soils under maize-wheat than in soils under agrohorticulture (81.3%) and agroforestry (77.8%). The mean SOC concentration decreased with the size of the dry stable aggregates (DSA) and water stable aggregates (WSA). In DSA, the mean SOC concentration was 58.06 and 24.2% higher in large and small macroaggregates than in microaggregates respectively; in WSA it was 295.6 and 226.08% higher in large and small macroaggregates than in microaggregates respectively in surface soil layer. The mean SOC concentration in surface soil was higher in DSA (0.79%) and WSA (0.63%) as compared to bulk soil (0.52%). The SOC concentration and stock being highest in soils under agroforestry resulted in higher SOC concentration in dry as well as WSA.     

The potential of REDD+ for carbon sequestration in tropical forests: Supply curves for carbon storage for Kalimantan,Indonesia

We study the potential of tropical multi-age multi-species forests for sequestering carbon in response to financial incentives from REDD+. Following existing carbon crediting schemes, the use of reduced impact logging techniques (RIL) allows a forest manager to apply for carbon credits whereas conventional logging (CL) does not. This paper is the first to develop a Hartman model with selective cutting in this setting that takes additionality of carbon sequestration explicitly into account. We apply the model using data for Kalimantan, Indonesia, for both private and government forest managers. The latter have a lower discount rate and are exempt from taxes. RIL leads to less damages on the residual stand than CL and has lower variable but higher fixed costs. We find that a system of carbon credits through REDD+ can increase carbon stored per hectare by 15.8% if the forest is privately managed and by 22% under government management if the carbon price equals the average 2015 price in the European Union's Emission Trading Scheme. Interestingly, awarding carbon credits to carbon stored in end-use wood products does not increase the amount of carbon stored, nor Land Expectation Value.     

Root distribution ofDactyladenia (Acioa) barteri andSenna (Cassia) Siamea in alley cropping on Ultisol. II. Impact on water regime and consequences for experimental design

Tensiometer measurements were carried out on a typic Paleudult in the humid forest zone of south eastern Nigeria in an alley cropping trial using fertilized and unfertilizedDactyladenia (Acioa) barteri andSenna (Cassia) siamea as hedgerow trees and a no-tree control. The interrow space of alley cropped and no-tree control plots were planted to maize/cassava intercrop. Water withdrawal during short dry spells and the dry season occurred fastest in the no-tree control plot and resembled the pattern in the adjacentS. siamea alley cropping. Previous root investigations showed that the whole no-tree control plot was within the range of root propagation of the adjacent hedgerow trees. Installation of a 70 cm deep root barrier led to a retarded water withdrawal in unfertilized no-tree control plots to a depth of 150 cm. In fertilized no-tree control this retardation occurred to a depth of 110 cm, while at 130 and 150 cm water withdrawal with root barriers was faster than without barriers. Results indicate thatS. siamea depleted water resources in the no-tree control plot and shortened the growing season of cassava. Restricting roots to the assigned plot size can reduce competition for water in adjacent plots even in layers below the depth of the barrier but can also induce compensative water withdrawal from layers which were not necessarily affected by the barrier. It appears that currently no standard methodology is available to conduct agroforestry trials without the risk of invalidation through root interference. Methods to determine minimum plot size in order to reduce the risk of invalidation and misinterpretation of results are suggested.     

Changes in dissolved organic matter with depth suggest the potential for postharvest organic matter retention to increase subsurface soil carbon pools

Research into postharvest management of forests often focuses on balancing the need for increased biomass yield against factors that may directly impact the productivity of the subsequent stand (e.g. nutrient and water availability, soil microclimate, etc.). Postharvest organic matter management, however, also exerts a strong influence over the translocation of carbon (C) into and through the soil profile and may provide a mechanism to increase soil C content. The effects of contrasting postharvest organic matter retention treatments (bole-only removal, BO; whole-tree removal, WT) on soil solution C concentration and quality were quantified at the Fall River and Matlock Long-term Soil Productivity (LTSP) studies in Washington state. Solutions were collected monthly at depths of 20 and 100 cm and analyzed for dissolved organic C (DOC), dissolved organic nitrogen (DON) and DOC:DON ratio. Comparisons of DOC concentrations with depth illustrate divergent trends between the two treatments, with an overall decrease in DOC with depth in the BO treatment and either an increase or no change with depth in the WT treatment. Trends in DON concentrations with depth were less clear, partly due to the very low concentrations observed, although the relationship of DOC:DON with depth shows a decrease in the BO treatment and little to no change in DOC quality in the WT treatment. This illustrates that more recalcitrant organic matter (higher DOC:DON) is being removed from solution as it moves through the soil profile. Only 35–40% of the DOC moving past 20 cm in the BO treatment is present at 100 cm. Conversely, 98–117% of the DOC at 20 cm in the WT treatment is present at 100 cm. Thus, 11 and 30 kg C ha⁻¹ yr⁻¹ are removed from solution between 20 and 100 cm in the BO treatment at the Matlock and Fall River LTSP studies, respectively. Although much of this C is often assumed to be utilized for microbial respiration, DOC:DON ratios of the potential organic substrates and the unique mineralogy of the soils of this region suggest that a significant portion may in fact be incorporated into a more recalcitrant soil C pool. Thus, postharvest organic matter retention may provide a mechanism to increase soil C sequestration on these soils.