Root distributions in a Grevillea robusta-maize agroforestry system in semi-arid Kenya

Limited knowledge of root distributions in agroforestry systems has resulted in assumptions that various tree species are more suited to agroforestry than others, because they are presumed to have few superficial lateral roots. This assumption was tested for Grevillea robusta when grown with maize (Zea mays) in an agroforestry system in a semi-arid region of Kenya. At a site with a shallow soil, root lengths of both species between the soil surface and bedrock were quantified by soil coring, at intervals over four cropping seasons, in plots containing sole stands and mixtures of the trees and crop; the trees were 4–6 years old and they were severely pruned before the third season. Profiles of soil water content were measured using a neutron probe. Prior to pruning of the trees, recharge of soil water below the deepest maize roots did not occur, resulting in significant (P<0.05) suppression of maize root lengths and downward root growth. Maximum root length densities for both species occurred at the top of the soil profile, reaching 1.1–1.7 cm cm^-3 for G. robusta, but only 0.5 cm cm^-3 for maize grown with trees. Root populations in mixed plots were dominated by G. robusta at all times, all depths and all distances from trees and maize and, thus, there was no spatial separation of the rooting zones of the trees and crop. Competition between G. robusta and maize for soil water stored near the surface was unavoidable, although pruning reduced its impact; complementary use of water by the trees and crop would only have been possible if alternative sources of water were available. This revised version was published online in June 2006 with corrections to the Cover Date.     

Root length dynamics in agroforestry with Gliricidia sepium as compared to sole cropping in the semi-deciduous rainforest zone of West Africa

Tree root systems may improve soil fertility through carbon inputs, uptake of leachable nutrients and maintenance of soil biomass, but can at the same time reduce crop yields by competition for water and nutrients. Quantitative information about the positive and negative effects of tree roots and their changes in space and time are necessary for the optimization of agroforestry associations. An alley cropping experiment was layed out as a randomized complete block design on a Plinthic Lixisol/Ferralic Cambisol with Gliricidia sepium hedgerows at 5 m distance, including a sole cropping control. The development of root systems was monitored by sequential soil coring (eight samplings) during one year, with maize and groundnut as crops. Additional information is presented from a single sampling for rice during the foregoing year. Pronounced fluctuations of live root length density indicated an important variability in the nutrient and water uptake capacity of the vegetation. At low total root length density, the hedgerows affected the root development in the agroforestry plots directly by the presence of their root systems. At high root length density, they affected root development mainly by improving crop root growth and influencing the composition of the spontaneous vegetation. The root length density of the hedgerows was too low to compete with the crops for soil resources. The hedgerows tended to increase root length densities in the subsoil when few roots were present, thus possibly reducing the risk of nutrient leaching. However, the length density of the perennial root systems decreased during the cropping season, presumably as an effect of repeated pruning, and attained minimum values almost at the same time as the crops. Trees with denser root systems which are less frequently pruned may be more efficient in achieving closer nutrient cycles, though at the cost of higher root competition with crops.     

Effects of periodic flooding and root pruning on Quercus nuttallii seedlings

In the southern United States, much of the emphasis in bottomland restoration is placed on establishing an oak-dominated forest. Artificial regeneration is an alternative for restoration on cleared lands and where a desirable seed source is not present. Currently the standard procedure for seedling preparation is to prune the roots prior to transplanting in the field. It is not fully known what effect(s) root pruning has on transplanted seedlings. In addition, bottomland restoration efforts inherently take place on floodplains. The potential interaction between root pruning and flooding on seedling performance is not known. This study consisted of two separate but related laboratory experiments. The purpose of the first experiment was to quantify the effects of various percentages of root removal and varying soil moisture regimes on transplanted Nuttall oak seedlings (Quercus nuttallii Palmer). Root pruning treatments consisted of removal of roots at 0%, 25% and 75% while soil moisture regime was maintained at non-flooded or periodically flooded conditions. Plant gas exchange, growth, and survival were measured. Root pruning alone had adverse effects on height growth during the first 72 days following transplanting. Periodic flooding also produced adverse effects on stomatal conductance (p = 0.0002), height growth (p = 0.005), and survival (p = 0.02). Photosynthetic data indicated that as pruning intensified in the periodically flooded seedlings, photosynthetic rates decreased. In contrast, as pruning intensified in the non-flooded seedlings, photosynthesis increased. This demonstrated that pruning rate had a varying effect on photosynthesis dependent upon soil moisture condition. Experiment 2 focused on the effects of varying degrees of root pruning on new root formation. The seedlings were grown under laboratory conditions, harvested at 0, 10, 20, and 30 days after treatment initiation, and analyzed for new root formation. Results of Experiment 2 indicated no difference in new root formation, root length, or root biomass due to the pruning treatment. Overall, our results from both experiments indicated that root pruning had no detectable long-term adverse effects on growth and survival of seedlings under drained soil conditions; however, as results from Experiment 1 demonstrated, if seedlings were planted in periodically flooded conditions, root pruning produced adverse effects. Thus, in restoration efforts utilizing Nuttall oak seedlings, the planting strategy and pruning rate should be carefully evaluated based on the knowledge of sites' hydrology. Alternatively, on sites with unpredictable flooding both pruned and unpruned seedlings may be utilized to ensure survival.     

Seedling vigour and the early growth of transplanted rice (Oryza sativa)

Previous studies suggest that the positive response of transplanted rice (Oryza sativa L.) to nursery fertiliser application was due to increased seedling vigour or possibly to increased nutrient content. This paper presents results of two glasshouse experiments designed to test the hypothesis that seedling vigour was responsible for the response of transplanted seedlings to nursery treatments. The aim of the present study was to explore the concept of seedling vigour of transplanted rice and to determine what plant attributes conferred vigour on the seedlings. Seedling vigour treatments were established by subjecting seedlings to short-term submergence (0, 1 and 2 days/week) in one experiment and to leaf clipping or root pruning and water stress in another to determine their effect on plant growth after transplanting. Submerging seedlings increased plant height but depressed shoot and root dry matter and root:shoot ratio of the seedling at 28 days after sowing. After transplanting these seedlings, prior submergence depressed shoot dry matter at 40 days. Nursery nutrient application increased plant height, increased root and shoot dry matter, but generally decreased root:shoot ratio. Pruning up to 60% of the roots at transplanting decreased shoot and root dry matter, P concentration in leaves at panicle initiation (PI) and straw dry matter and grain yield at maturity. By contrast, pruning 30% of leaves depressed shoot and root dry matter by 30% at PI, and root dry matter and straw and grain yield by 20% at maturity. The combined effects of leaf clipping and root pruning on shoot, root and straw dry matter were largely additive. It is concluded that the response of rice yield to nursery treatments is largely due to increased seedling vigour and can be effected by a range of nutritional as well as non-nutritional treatments of seedlings that increase seedling dry matter, nutrient content, and nutrient concentration. Impairment of leaf growth and to a lesser extent root growth in the nursery depressed seedling vigour after transplanting. However, rather than increasing stress tolerance, seedling vigour was more beneficial when post transplant growth was not limited by nutrient or water stresses.     

Fresh root decomposition pattern of two contrasting tree species from temperate agroforestry systems: effects of root diameter and nitrogen enrichment of soil

Fresh tree root decomposition induced by tillage is an important source of soil nutrients in agroforestry systems. Here we examined the effects of tree species, root size and soil N enrichment on fresh root decomposition under laboratory conditions. Fresh roots with two diameters (<2 and 2?C5 mm) of Populus euramericana cv. ??N3016?? (poplar) and Pinus tabulaeformis (pine) collected from agroforestry systems in Northeast China were used in the experiment. For each root treatment, four N levels (0, 50, 100 and 150 ??g N g^?1 soil) were added. We recognized N concentration and C/N ratio as the root quality variables, and determined decomposition rates as cumulative CO₂ production and mass loss. Poplar roots had higher N concentration and lower C/N ratio and decomposed faster than pine roots, and smaller roots decomposed faster than the corresponding larger roots. The effect of N addition on root decomposition varied from positive to negligible to negative, and depended on root quality and N addition rates. Increased N availability did not accelerate and even suppressed poplar root decomposition, whereas generally stimulated pine root decomposition. Our results suggest that root quality should be incorporated into the design of agroforestry systems. Moreover, the differential responses of N addition on decomposition of fresh roots with different quality provide insights into soil nutrient management in agroforestry practices.     

Subsoil root activity in tree-based cropping systems

An increasing number of studies indicate that (i) nutrient and water resources can be abundant in the subsoil and (ii) trees have deep root systems that can possibly reach these resources. It is less clear whether subsoil resources are actually improving water and nutrient status of tree-based cropping systems and whether they are significantly increasing crop production and yield. To answer such a question, the distribution of nutrient and water uptake by trees needs to be quantified. So-called `root activity distributions' give valuable information about actual subsoil use by trees whereas studies on root length or mass distributions do not often correlate with uptake distributions. Despite the usually lower relative root activity in the subsoil compared to the topsoil per unit soil, the large volume of subsoil in comparison to mostly shallow topsoil is an important resource for crop nutrient and water uptake. The present study compares published root activity distributions using the model Activity=A _max(1–k ^depth). The obtained regression constants k of 0.91–0.99 determined in this publication reflect the values computed by an earlier published survey for root biomass ranging from tundra to those of temperate forest biomes. Thus, tree crops can have shallow root activity and 75% of their total root activity in the first 0.1 m of soil, or very deep root activity with more than 90% below 0.1 m. Neither environmental factors (i.e., climate and soil properties available from these publications) nor plant species explain differences of root activity distributions with depth. The deepest root activity is found for fruit trees such as citrus, guava and mango. Shaded crops such as coffee and cacao tend to have shallower root activity than fruit trees. Monocots including oil palm, coconut or banana have root activity that can be both deep and shallow. Regional and temporal variations of subsoil root activity for the same tree species are significant and generally larger than differences between species. Root activity patterns of tree crops appear to be sufficiently flexible to allow for subsoil resource use. Consequently, management such as pruning, fertilization, liming and irrigation are shown to significantly affect subsoil root activity.     

Effect of five tree crops and a cover crop in multi-strata agroforestry at two fertilization levels on soil fertility and soil solution chemistry in central Amazonia

The spatio-temporal patterns of soil fertility and soil solution chemistry in a multi-strata agroforestry system with perennial crops were analysed as indicators for the effects of crop species and management measures on soil conditions under permanent agriculture in central Amazonia. The study was carried out in a plantation with locally important tree crop species and a leguminous cover crop at two fertilization levels on a xanthic Ferralsol. Soil fertility to 2 m soil depth was evaluated 3.5 years after the establishment of the plantation, and soil solution chemistry at 10, 60 and 200 cm soil depth was monitored over 2 years. Several soil fertility characteristics exhibited spatial patterns within the multi-strata plots which reflected the differing properties of the plant species and their management, including the fertilizer input. Significant differences between species could be detected to 150 cm depth, and between fertilization treatments to 200 cm depth. Favourable effects on nutrient availability in the soil were found for annatto (Bixa orellana) (P, K) and cupuaçu (Theobroma grandiflorum) (Ca, Mg) in comparison with peach palm (Bactris gasipaes) and Brazil nut (Bertholletia excelsa). Nutrient concentrations of the soil solution showed pronounced fluctuations in the topsoil, corresponding to fertilizer applications. Large nutrient concentrations in the soil solution were accompanied by increased concentrations of aluminium and low pH values, caused by exchange reactions between fertilizer and sorbed acidity and reinforced by the acidifying effect of nitrification. The soil solution under the leguminous cover crop Pueraria phaseoloides had relatively large N concentrations during periods when those under the tree crops were small, and this could partly explain why no yield responses to N fertilization were observed at this site.     

Authors index

In a runoff irrigation system in Northern Kenya, we studied the nutrient interactions of sole cropped and alley cropped Sorghum bicolor (L.) Moench and Acacia saligna (Labill.) H.L. Wendl. The trees were pruned once before the cropping season and the biomass was used as fodder for animals. The nutrient contents in leaf tissue, soil and soil solution were monitored and the uptake of applied tracers (¹⁵N, Sr) was followed. The grain yield of alley cropped sorghum was similar to or slightly higher than in monoculture and did not decrease near the tree-crop interface. Foliar N and Ca contents of the crop were higher in the agroforestry combination than in monoculture, corresponding to higher soil N and Ca contents. Soil solution and soil mineral N dynamics indicate an increase of N under the tree row and unused soil N at the topsoil in the alley of the sole cropped trees as well as below 60 cm depth in the crop monoculture. The N use efficiency of the tree+crop combination was higher than the sole cropped trees or crops. Competition was observed for Zn and Mn of both tree and crop whereas for Ca only the tree contents decreased. P, K, Mg and Fe dynamics were not affected by alley cropping at our site. The lower uptake of applied Sr by trees in alley cropping compared to those of the monoculture stand suggested a lower competitiveness of the acacia than sorghum, which did not show lower Sr contents when intercropped. The study showed the usefulness of combining soil and plant analyses together with tracer techniques identifying nutrient competition, nutrient transfer processes and the complementary use of soil nutrients, as the main features of the tree-crop combination. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phosphorus nutrition and water deficits in field-grown soybeans

Phosphorus and water deficits are important limiting factors in agricultural production. A field experiment was carried out with soybean (Glycine max (L.) Merr.) to determine whether the effect of water stress on field-grown soybean changes with soil P availability, and whether soil water content affects plant P nutrition. The soil was a Sadler series (fine-silty, mixed, mesic Glossic Fragiudalf) located at Princeton, Kentucky, USA (37°60′ north, 87°60′ west). The experiment was a factorial with three levels of soil P availability (4, 19 and 32 mg kg⁻¹, Mehlich III) and two of water (irrigated and non-irrigated). Most of the effects of phosphorus and water stress on soybean growth were additive, so that, in general, effects of water stress were similar at each P level. Phosphorus deficiency slowed vegetative development, reduced shoot growth, LAI, P absorption and concentration, seed number, size and yield, and increased root length density in the surface soil. Water stress accelerated crop maturity, reduced shoot growth, LAI, P absorption and concentration, seed number, size and yield, and increased root length density. Some interactions between P and water were observed. Water stress slowed vegetative development only at the lowest P level (P0). The crop had a positive response to increasing P availability in both situations, with and without irrigation, suggesting that P addition would be justified even when a dry growing season is likely to occur. This revised version was published online in June 2006 with corrections to the Cover Date.     

Competition in tree row agroforestry systems. 1. Distribution and dynamics of fine root length and biomass

Complementarity in the distribution of tree and crop root systems is important to minimise competition for resources whilst maximising resource use in agroforestry systems. A field study was conducted on a kaolinitic Oxisol in the sub-humid highlands of western Kenya to compare the distribution and dynamics of root length and biomass of a 3-year-old Grevillea robusta A. Cunn. ex R. Br. (grevillea) tree row and a 3-year-old Senna spectabilis DC. (senna) hedgerow grown with Zea mays L. (maize). Tree roots were sampled to a 300 cm depth and 525 cm distance from the tree rows, both before and after maize cropping. Maize roots were sampled at two distances from the tree rows (75–150 cm and 450–525 cm) to a maximum depth of 180 cm, at three developmental stages. The mean root length density (L_rv) of the trees in the upper 15 cm was 0.55 cm cm⁻³ for grevillea and 1.44 cm cm⁻³ for senna, at the start of the cropping season. The L_rv of senna decreased at every depth during the cropping season, whereas the L_rv of grevillea only decreased in the crop rooting zone. The fine root length of the trees decreased by about 35% for grevillea and 65% for senna, because of maize competition, manual weeding, seasonal senescence or pruning regime (senna). At anthesis, the L_rv of maize in the upper 15 cm was between 0.8 and 1.5 cm cm⁻³. Maize root length decreased with greater proximity to the tree rows, potentially reducing its ability to compete for soil resources. However, the specific root length (m g⁻¹) of maize was about twice that of the trees, so may have had a competitive uptake advantage even when tree root length was greater. Differences in maize fine root length and biomass suggest that competition for soil resources and hence fine root length may have been more important for maize grown with senna than grevillea. This revised version was published online in June 2006 with corrections to the Cover Date.     

Intercropping Competition between Apple Trees and Crops in Agroforestry Systems on the Loess Plateau of China

Agroforestry has been widely practiced in the Loess Plateau region of China because of its prominent effects in reducing soil and water losses, improving land-use efficiency and increasing economic returns. However, the agroforestry practices may lead to competition between crops and trees for underground soil moisture and nutrients, and the trees on the canopy layer may also lead to shortage of light for crops. In order to minimize interspecific competition and maximize the benefits of tree-based intercropping systems, we studied photosynthesis, growth and yield of soybean (Glycine max L. Merr.) and peanut (Arachis hypogaea L.) by measuring photosynthetically active radiation, net photosynthetic rate, soil moisture and soil nutrients in a plantation of apple (Malus pumila M.) at a spacing of 4 m × 5 m on the Loess Plateau of China. The results showed that for both intercropping systems in the study region, soil moisture was the primary factor affecting the crop yields followed by light. Deficiency of the soil nutrients also had a significant impact on crop yields. Compared with soybean, peanut was more suitable for intercropping with apple trees to obtain economic benefits in the region. We concluded that apple-soybean and apple-peanut intercropping systems can be practical and beneficial in the region. However, the distance between crops and tree rows should be adjusted to minimize interspecies competition. Agronomic measures such as regular canopy pruning, root barriers, additional irrigation and fertilization also should be applied in the intercropping systems.     

华北低丘山区果药复合系统种间水分利用策略

了解林农复合系统的种间水分关系至关重要.该文通过稳定氘同位素研究了华北低丘山区核桃(Juglans regia)-菘蓝(Isatis tinctoria)/决明(Senna tora)复合系统各组分的水分来源, 试图明确该果药复合系统的种间水分利用策略, 为该区林农配置模式的选择提供理论依据.研究结果表明: 果药复合系统的土壤含水量明显高于单作菘蓝和单作决明地块, 在2012年,2013年上半年比单作菘蓝高26.74%和7.93%, 在下半年比单作决明高17.39%和13.65%.在果药复合系统内部, 土壤含水量以核桃树行中间位置的最低,树行北侧和树下最高.在各个土层深度, 单作系统的土壤水氢稳定同位素比率(δD值)均比复合系统的高.在菘蓝生长时期的春旱期, 复合系统中核桃的大部分水分来源于30-80 cm深层土壤水, 表明此时期核桃表层根系活性不高; 而决明生长时期正值雨季, 此时核桃优先利用雨水补充的0-30 cm浅层土壤水,表层根系活性增强.在任何生长时期, 菘蓝和决明85%以上的水分都来自浅层土壤水.在菘蓝苗期, 其根系尚未扎入深层土壤中, 单作菘蓝的水分完全来源于浅层土壤, 而在2012年间作菘蓝却有5.7%的水分来自于深层土壤, 在更为干旱的2013年该比例上升到9.7%, 该结果证实了核桃在旱季存在"水力提升"作用, 供浅根系作物吸收利用, 并且越干旱, 该水力提升作用越强.在华北低丘山区核桃-菘蓝/决明复合系统中, 深根性核桃改善了复合系统的土壤水分状况, 在旱季主要利用深层土壤水以避开与浅层作物的水分竞争,并能将深层土壤水提升至浅层土壤供菘蓝吸收利用, 核桃与两种药材表现为水分互利关系, 因而该模式适合在该地区发展.     

Interspecific water use strategies of a Juglans regia and Isatis tinctoria/Senna tora agroforestry

Aims Understanding the interspecific water relations is important for designing agroforestry systems. The objective of this study was to determine the water use strategies of component species in a walnut (Juglans regia)-woad (Isatis tinctoria)/sicklepod (Senna tora) agroforestry system.Methods Water sources of component species in a walnut-woad/sicklepod agroforestry system were investigated with the technique of stable deuterium isotope tracing at a site of hilly area in Northern China during 2012-2013.Important findings Results showed that the soil water content in the agroforestry system was 26.74% and 7.93% greater than in the pure woad field in the first half year, and 17.39% and 13.65% greater than in the pure sicklepod field in the second half year (sicklepod growth period), in 2012 and 2013, respectively. The lowest water content was found in the middle of tree rows, and the highest water content was found in the northern side of tree rows or under the trees. In the soil layers measured, the pure woad and pure sicklepod systems had greater hydrogen stable isotope ratios (δ D value) of soil water than in the agroforestry system. During the period of woad growth, more than half of the water absorbed by walnut was from the deeper soil layer (30-80 cm). In contrast, the walnut trees mainly utilized shallow layer (0-30 cm) soil water during the period of sicklepod growth. These findings suggest that walnut has a two-state root system: during the period of woad growth, shallow roots of walnut are not active when soil is dry whereas the sicklepod growth occur in rainy season, and the shallow roots of walnut are active and utilize more shallow soil water supplemented by rainwater. More than 85% of water used by both the woad and the sicklepod were from the shallow layer soil. At the seedling stage, the roots of woad, cannot grow into the deeper soil layer, and the absorbed water is completely from the shallow layer in the pure woad system. However, 5.7% of the water absorbed by the intercropped woad was from the deeper soil layer in 2012, and the proportion increased further (9.7%) in the following year when there was less precipitation. The results confirmed that hydraulic lift effect of walnut occurred on shallow layer crop in dry season, and this effect become greater under drier conditions. Therefore, deeper roots of walnut improved water condition in the walnut- woad/sicklepod agroforestry systems compared to pure crop systems. The walnut mainly utilized water from the deeper layer to avoid water competition with the shallow layer. In the dry season, crops benefited from the water provided by walnut roots through hydraulic lift. Walnut and intercropped plants exhibited water facilitation in the agroforestry systems, suggesting that this configuration is a suitable practice in this area.     

Above-ground nitrogen dynamics following the complete pruning of a nodulated woody legume in humid tropical field conditions

Above-ground nitrogen fluxes following a complete pruning of the neotropical agroforestry tree Erythrina poeppi-giana (Walpers) O.F. Cook (Leguminosae: Phaseoleae) were studied during pruning intervals of 26 and 23 weeks in the humid tropics of Costa Rica. The experiment included four clones and a half-sib family of the species. The leaf-level N fluxes were modelled as a function of leaf age, and were scaled to the canopy level on the basis of the leaf age distribution. The N content of young leaves increased exponentially, followed by relatively small changes at maturity. Slight net N retranslocation started at the middle of leaf life span, but a major N efflux occurred only a few days before leaf shedding. It was estimated that, depending on the tree source, 29-44& of the total N accumulation in the above-ground biomass occurred during 11 weeks after pruning (WAP), before initiation of nodulation. The nodule biomass peaked at the time leaf shedding started (15–17 WAP). Considerable rapid N efflux from the foliage was observed at this time, suggesting regulation of nodulation by a feedback from the foliage. The implications of the N economy of E. poep-pigiana on its management in agroforestry systems are discussed.     

Effect of Plant Species on Persistence of Paecilomyces lilacinus Strain 251 in Soil and on Root Colonization by the Fungus

The effect of 12 plant species on the persistence of Paecilomyces lilacinus strain 251 in soil was investigated. After incorporating formulated conidia into non-sterile soil followed by transplanting different test plants, the population dynamic of the fungus was determined over 100 days. At termination of the experiment, the fungal population in the planted soil was compared to the density of P. lilacinus in the rhizosphere and the percent increase or decrease was calculated for each crop. In addition, the potential of P. lilacinus strain 251 to colonize roots endophytically was investigated. Comparison of the slopes describing the population dynamics of the fungus showed no significant differences between soil without plants and soil from the root zone of the majority of the test plants. Bean was the only plant species consistently exerting a negative effect on the persistence of P. lilacinus strain 251 in the soil. For the first time, P. lilacinus strain 251 was isolated in significant numbers from healthy root tissue of barley plants.     

Roots,soil water and crop yield: tree crop interactions in a semi-arid agroforestry system in Kenya

Variations in soil water, crop yield and fine roots of 3–4 year-old Grevillea robusta Cunn. and Gliricidia sepium (Jacq.) Walp. growing in association with maize (Zea mays L.) were examined in semiarid Kenya during the long rains of 1996 and 1997. Even although tree roots penetrated more deeply than maize roots, maximum root length densities for both tree species and maize occurred in the top 200 mm of the soil profile where soil moisture was frequently recharged by rains. Populations of roots in plots containing trees were dominated by tree roots at the beginning of the growing season but because tree roots died and maize root length increased during the cropping season, amounts of tree and maize roots were similar at the end of the season. Thus, there was evidence of temporal separation of root activity between species, but there was no spatial separation of the rooting zones of the trees and crops within that part of the soil profile occupied by crop roots. Tree root length density declined with increasing distances from rows of trees and with depth in the soil profile. Although Grevillea trees were largest, plots containing G. sepium trees always contained more tree roots than plots containing G. robusta trees and Gliricidia was more competitive with maize than Grevillea. Overall, Gliricidia reduced crop yield by about 50% and Grevillea by about 40% relative to crop yield in control plots lacking trees and reductions of crop yield were greatest close to trees. There was less soil moisture in plots containing trees than in control plots. Such difference between control plots and plots containing trees were maximal at the end of the dry season and there was always less soil moisture close to trees than elsewhere in the plots. Plots containing Gliricidia trees contained less soil water than plots containing Grevillea trees.     

Main interspecific competition and land productivity of fruit-crop intercropping in Loess Region of West Shauxi

Taking the four typical fruit-crop intercropping models, i.e., walnut-peanut, walnut-soybean, apple-peanut, and apple-soybean, in the Loess Region of western Shanxi Province as the objects, this paper analyzed the crop (peanut and soybean) photosynthetic active radiation (PAR), net photosynthetic rate (P(n)), yield, and soil moisture content. Comparing with crop monoculture, fruit-crop intercropping decreased the crop PAR and P(n). The smaller the distance from tree rows, the smaller the crop PAR and P(n). There was a significantly positive correlation between the P(n) and crop yield, suggesting that illumination was one of the key factors affecting crop yield. From the whole trend, the 0-100 cm soil moisture content had no significant differences between walnut-crop intercropping systems and corresponding monoculture cropping systems, but had significant differences between apple-crop intercropping systems and corresponding monoculture cropping systems, indicating that the competition for soil moisture was more intense in apple-crop intercropping systems than in walnut-crop intercropping systems. Comparing with monoculture, fruit-crop intercropping increased the land use efficiency and economic benefit averagely by 70% and 14%, respectively, and walnut-crop intercropping was much better than apple-crop intercropping. To increase the crop yield in fruit-crop intercropping systems, the following strategies should be taken: strengthening the management of irrigation and fertilization, increasing the distances or setting root barriers between crop and tree rows, regularly and properly pruning, and planting shade-tolerant crops in intercropping.     

Root distribution and water uptake patterns of corn under surface and subsurface drip irrigation

Information on root distribution and uptake patterns is useful to better understand crop responses to irrigation and fertigation, especially with the limited wetted soil volumes which develop under drip irrigation. Plant water uptake patterns play an important role in the success of drip irrigation system design and management. Here the root systems of corn were characterized by their length density (RLD) and root water uptake (RWU). Comparisons were made between the spatial patterns of corn RWU and RLD under surface and subsurface drip irrigation in a silt loam soil, considering a drip line on a crop row and between crop rows. Water uptake distribution was measured with an array of TDR probes at high spatial and temporal resolution. Root length density was measured by sampling soil cores on a grid centered on crop row. Roots were separated and an estimation of root geometrical attributes was made using two different image analysis programs. Comparisons of these programs yielded nearly identical estimates of RLD. The spatial patterns of RWU and RLD distributions, respectively normalized to the total uptake and root length, were generally similar only for drip line on a crop row, but with some local variations between the two measures. Both RLD and RWU were adequately fitted with parametric models based on semi-lognormal and normal Gaussian bivariate density functions (Coelho and Or, 1996; Soil Sci. Soc. Am. J. 60, 1039–1049).     

Phosphorus mobilization in agroforestry: Organic anions,phosphatase activity and phosphorus fractions in the rhizosphere

Plant and Soil - In agroforestry systems on Ferralsols in the tropics, maize crop yields are low owing to a lack of P. However, some agroforestry tree species adapted to P-fixing soils may be able...     

The response of sorghum and sunflower to short-term waterlogging

Summary Sorghum and sunflower were waterlogged for nine days during the vegetative, floral initiation/buds-visible or anthesis stage of growth under glasshouse conditions to observe the effects on root growth and development. In addition, some plants were waterlogged at all three stages to observe any adaptations induced by waterlogging. The most marked effects occurred at the initiation/buds-visible stage where a 30% reduction in root length and a 40% reduction in root dry weight of sorghum occurred with comparable figures for sunflower being 50 and 60% respectively. Generally, sorghum roots had a higher porosity than sunflower which may contribute to its greater tolerance to waterlogging. The observed changes in root growth are discussed in relation to previously documented effects of waterlogging on growth of the two species and changes which occur in the soil environment.