Effect of Crotalaria juncea Amendment on Nematode Communities in Soil with Different Agricultural Histories

Effect of sunn hemp (Crotalaria juncea) hay amendment on nematode community structure in the soil surrounding roots of yellow squash (Cucurbita pepo) infected with root-knot nematodes was examined in two greenhouse experiments. Soils were from field plots treated long-term (LT) with yard-waste compost or no yard-waste compost in LT experiment, and from a short-term (ST) agricultural site in ST experiment. Soils collected were either amended or not amended with C. juncea hay. Nematode communities were examined 2 months after squash was inoculated with Meloidogyne incognita. Amendment increased (P < 0.05) omnivorous nematodes in both experiments but increased only bacterivorous nematodes in ST experiment (P < 0.05), where the soil had relatively low organic matter (<2%). This effect of C. juncea amendment did not occur in LT experiment, in which bacterivores were already abundant. Fungivorous nematodes were not increased by C. juncea amendment in either experiment, but predatory nematodes were increased when present. Although most nematode faunal indices, including enrichment index, structure index, and channel index, were not affected by C. juncea amendment, structure index values were affected by previous soil organic matter content. Results illustrate the importance of considering soil history (organic matter, nutrient level, free-living nematode number) in anticipating changes following amendment with C. juncea hay.     

改良剂对酸性土壤上伴矿景天铝毒缓解作用及镉锌吸收性的影响

为探究不同改良剂对酸性土壤铝(Al)胁迫条件下镉(Cd)锌(Zn)超积累植物伴矿景天Sedum plumbizincicola生长以及镉和锌吸取修复效率的影响,分别添加不同种类改良剂(钙镁磷肥(CMP)、MgCO3、KH2PO4)和不同浓度CMP进行温室盆栽试验。结果表明,CMP能够一定程度上提高土壤pH值并降低土壤交换性Al的浓度,MgCO3能够显著提高土壤pH值和降低土壤交换性Al的浓度,KH2PO4能够降低土壤中交换性Al浓度但未改变土壤pH值。施用适量的CMP(9.39 mg/kg)能够提高伴矿景天生物量和Cd、Zn吸取修复效率,用量过高会抑制伴矿景天生长和Cd、Zn修复效率;施用MgCO3可增大伴矿景天生物量和Cd、Zn修复效率,施用KH2PO4反而抑制了伴矿景天生长。酸性土壤上施用适量的CMP和MgCO3能够缓解伴矿景天的铝毒作用,维持较高的重金属吸收效率。     

Major limitations to achieving “4 per 1000” increases in soil organic carbon stock in temperate regions: Evidence from long‐term experiments at Rothamsted Research,United Kingdom

We evaluated the “4 per 1000” initiative for increasing soil organic carbon (SOC) by analysing rates of SOC increase in treatments in 16 long‐term experiments in southeast United Kingdom. The initiative sets a goal for SOC stock to increase by 4‰ per year in the 0–40 cm soil depth, continued over 20 years. Our experiments, on three soil types, provided 114 treatment comparisons over 7–157 years. Treatments included organic additions (incorporated by inversion ploughing), N fertilizers, introducing pasture leys into continuous arable systems, and converting arable land to woodland. In 65% of cases, SOC increases occurred at >7‰ per year in the 0–23 cm depth, approximately equivalent to 4‰ per year in the 0–40 cm depth. In the two longest running experiments (>150 years), annual farmyard manure (FYM) applications at 35 t fresh material per hectare (equivalent to approx. 3.2 t organic C/ha/year) gave SOC increases of 18‰ and 43‰ per year in the 23 cm depth during the first 20 years. Increases exceeding 7‰ per year continued for 40–60 years. In other experiments, with FYM applied at lower rates or not every year, there were increases of 3‰–8‰ per year over several decades. Other treatments gave increases between zero and 19‰ per year over various periods. We conclude that there are severe limitations to achieving the “4 per 1000” goal in practical agriculture over large areas. The reasons include (1) farmers not having the necessary resources (e.g. insufficient manure); (2) some, though not all, practices favouring SOC already widely adopted; (3) practices uneconomic for farmers—potentially overcome by changes in regulations or subsidies; (4) practices undesirable for global food security. We suggest it is more realistic to promote practices for increasing SOC based on improving soil quality and functioning as small increases can have disproportionately large beneficial impacts, though not necessarily translating into increased crop yield.     

Establishment of a Vegetation Cover on Tundra Kimberlite Mine Tailings: 1. A Greenhouse Study

High erosion potential of dewatered kimberlite mine tailings after diamond extraction has prompted research at the Ekati Diamond Mine in the Canadian subarctic heath tundra ecosystem. Coarse texture, no organic component, lack of available macronutrients, and a serpentine chemistry are the principal limitations of these kimberlite tailings to plant colonization. Structure‐improving (peat moss, lake sediment, sewage sludge, Agri‐Boost, and composted papermill sludge) and nutrient‐providing (fertilizer, calcium carbonate, gypsum, and rock phosphate) amendments were tested in the greenhouse to ameliorate these limitations, thereby facilitating the field establishment of a permanent vegetation cover, which would stabilize the surface materials and promote natural colonization by the surrounding tundra vegetation. Seven native grass species (Arctagrostis latifolia, Calamagrostis canadensis, Poa glauca, Poa alpina, Deschampsia beringensis, Deschampsia caespitosa, and Festuca rubra) were used to measure amendment success. With the addition of structure‐improving and nutrient‐providing amendments, plant growth on kimberlite tailings was significantly enhanced. Tailings properties, including cation exchange capacity, percentage of organic carbon, and macronutrient availability, were also improved by amendment addition.     

Carbon Sequestration in Reclaimed Minesoils

Minesoils are drastically influenced by anthropogenic activities. They are characterized by low soil organic matter (SOM) content, low fertility, and poor physicochemical and biological properties, limiting their quality, capability, and functions. Reclamation of these soils has potential for resequestering some of the C lost and mitigating CO₂ emissions. Soil organic carbon (SOC) sequestration rates in minesoils are high in the first 20 to 30 years after reclamation in the top 15 cm soil depth. In general, higher rates of SOC sequestration are observed for minesoils under pasture and grassland management than under forest land use. Observed rates of SOC sequestration are 0.3 to 1.85 Mg C ha^{? 1} yr^{? 1} for pastures and rangelands, and 0.2 to 1.64 Mg C ha^{? 1} yr^{? 1} for forest land use. Proper reclamation and postreclamation management may enhance SOC sequestration and add to the economic value of the mined sites. Management practices that may enhance SOC sequestration include increasing vegetative cover by deep-rooted perennial vegetation and afforestation, improving soil fertility, and alleviation of physical, chemical and biological limitations by fertilizers and soil amendments such as biosolids, manure, coal combustion by-products, and mulches. Soil and water conservation are important to SOC sequestration. The potential of SOC sequestration in minesoils of the US is estimated to be 1.28 Tg C yr^?1, compared to the emissions from coal combustion of 506 Tg C yr^{? 1}.     

Deep soil inventories reveal that impacts of cover crops and compost on soil carbon sequestration differ in surface and subsurface soils

Increasing soil organic carbon (SOC) via organic inputs is a key strategy for increasing long‐term soil C storage and improving the climate change mitigation and adaptation potential of agricultural systems. A long‐term trial in California's Mediterranean climate revealed impacts of management on SOC in maize‐tomato and wheat–fallow cropping systems. SOC was measured at the initiation of the experiment and at year 19, at five depth increments down to 2 m, taking into account changes in bulk density. Across the entire 2 m profile, SOC in the wheat–fallow systems did not change with the addition of N fertilizer, winter cover crops (WCC), or irrigation alone and decreased by 5.6% with no inputs. There was some evidence of soil C gains at depth with both N fertilizer and irrigation, though high variation precluded detection of significant changes. In maize?tomato rotations, SOC increased by 12.6% (21.8 Mg C/ha) with both WCC and composted poultry manure inputs, across the 2 m profile. The addition of WCC to a conventionally managed system increased SOC stocks by 3.5% (1.44 Mg C/ha) in the 0–30 cm layer, but decreased by 10.8% (14.86 Mg C/ha) in the 30–200 cm layer, resulting in overall losses of 13.4 Mg C/ha. If we only measured soil C in the top 30 cm, we would have assumed an increase in total soil C increased with WCC alone, whereas in reality significant losses in SOC occurred when considering the 2 m soil profile. Ignoring the subsoil carbon dynamics in deeper layers of soil fails to recognize potential opportunities for soil C sequestration, and may lead to false conclusions about the impact of management practices on C sequestration.     

Immobilization of Heavy Metals in Soil Using Natural and Waste Materials for Vegetation Establishment on Contaminated Sites

Contaminated land is increasingly becoming an important issue worldwide. Many contaminants are persistent in soil for a large number of years. With the increase in public awareness regarding the consequences of contaminated soil, many researchers are concentrating on developing cost-effective and socially acceptable soil remediation technologies. Soils of many sites, which have been left derelict after industrial decline, harbor a broad suite of metal and organic contaminants. Land where such contaminants are deemed to pose a significant risk to receptors is considered contaminated under modern guidance. Remediation to break identified pollutant linkages would precede reclamation and plant establishment. One approach to break the pollutant receptor linkage is to utilize materials that effectively create soil conditions that immobilize contaminants whilst providing essential plant growth properties in terms of nutrition and water holding capacity. Materials that may achieve this include: 1) composts derived from materials such as sewage sludges and other municipal sources; 2) natural or synthetic zeolites; or 3) industrial by-products such as red-mud or other iron-rich materials such as iron grit or iron oxyhydroxides. Remediation techniques that utilize such materials may be cost-effective compared to more traditional methods and may effectively divert materials from the waste stream and could thereby make a dual contribution to sustainable development.     

Slash Pile Burning Effects on Soil Biotic and Chemical Properties and Plant Establishment: Recommendations for Amelioration

Ponderosa pine forest restoration consists of thinning trees and reintroducing prescribed fire to reduce unnaturally high tree densities and fuel loads to restore ecosystem structure and function. A current issue in ponderosa pine restoration is what to do with the large quantity of slash that is created from thinning dense forest stands. Slash piling burning is currently the preferred method of slash removal because it allows land managers to burn large quantities of slash in a more controlled environment in comparison with broadcast burning slash. However burning slash piles is known to have adverse effects such as soil sterilization and exotic species establishment. This study investigated the effects of slash pile burning on soil biotic and chemical variables and early herbaceous succession on burned slash pile areas. Slash piles were created following tree thinning in two adjacent approximately 20‐ha ponderosa pine (Pinus ponderosa) restoration treatments in the Coconino National Forest near Flagstaff, Arizona. We selected 30 burned slash pile areas and sampled across a gradient of the burned piles for arbuscular mycorrhizal (AM) propagule densities, the soil seed bank, and soil chemical properties. In addition, we established five 1‐m² plots in each burned pile to quantify the effect of living soil (AM inoculum) and seeding amendments on early herbaceous succession in burned slash pile areas. The five treatments consisted of a control (no treatment), living soil (AM inoculum) amendment, sterilized soil (no AM inoculum) amendment, seed amendment, and a seed/soil (AM inoculum) amendment. Slash pile burning nearly eliminated populations of viable seeds and AM propagules and altered soil chemical properties. Amending scars with native seeds increased the cover of native forbs and grasses. Furthermore adding both seed and living soil more than doubled total native plant cover and decreased ruderal and exotic plant cover. These results indicate that seed/soil amendments that increase native forbs and grasses may enhance the rate of succession in burned slash pile areas by allowing these species to outcompete exotic and ruderal species also establishing at the site through natural regeneration.     

LEAD PHYTOEXTRACTION BY WHEAT IN RESPONSE TO THE EDTA APPLICATION METHOD

Lead solubilization in soil and accumulation by spring wheat (Triticum aestivum L.) was studied in response to the ethylenediaminetetraacetic acid (EDTA) application method. In this study, 4 mmol EDTA kg^?1 was applied using two application methods (a single dose and split doses) either alone or in combination with elemental sulfur. Results indicate that the application of EDTA in four equal splits at 1 mmol kg^?1 during the growth period resulted in significantly higher shoot dry matter than its application at 4 mmol kg^?1 at once 10 d before harvesting the wheat crop at the bolting stage. EDTA applied in split doses resulted in less lead (Pb) solubilization as compared with the single-dose application. The split application also significantly increased the shoot Pb concentration and Pb accumulation by wheat shoots as compared with the single-dose application. Despite its lesser effect on Pb solubilization, the EDTA application in split doses substantially increased Pb accumulation; thus, it is expected to minimize the risk of groundwater contamination.     

Evaluation of powdered pine bark for control ofMeloidogyne arenaria andHeterodera glycines on soybean

Commercially avaiable pine bark nuggets (composted) and fresh pine bark were ground into powders and added at rates of 0 to 50 g kg^–1 to field soil infested withMeloidogyne arenaria andHeterodera glycines. The treated soil was maintained moist in the greenhouse for 2 weeks, sampled, and planted with Davis soybean (Glycine max.). Eight weeks after planting, numbers ofM. arenaria andH. glycines in soil decreased with increasing amounts of composted or fresh pine bark. No juveniles were present in soil treated with 5% pine bark. The number of galls and cysts g^–1 root decreased in proportion to the amount of pine bark added to soil. Gall and cyst formation was completely eliminated at the 5% rate. Numbers of saprophagous nematodes were highest in soil with 4–5% pine bark. The activity of several soil enzymes was correlated with the addition of both composted and fresh pine bark. Fresh pine bark powder caused an increase in soil enzyme activity compared to composted pine bark, but did not provide consistent control of gall and cyst formation.Journal Series No. 18-933579 Alabama Agricultural Experiment Station