Available N and P,Microbial Activity,and Biomass in Saline Sandy and Clayey Soils Amended with Residues of Wheat and Alfalfa

Salt accumulation has a negative effect on microorganisms, but plant residues may enhance the microbial activity and biomass. An experiment was conducted over 50 days to evaluate the effect of wheat and alfalfa residues on microbial activity and biomass and nitrogen (N) and phosphorus (P) availability in sandy and clayey soils at different salinity levels. Equivalent amounts of calcium (Ca⁺²) and sodium (Na⁺) salts were added to both soils. Values of electrical conductivity (EC_1:5), denoted S1, S2, and S3 in each soil, were 0.16, 1.10 and 1.98 dS m^?1 in the sand and 0.19, 0.82 and 1.75 dS m^?1 in the clay. Residues of wheat and alfalfa were added at 2% (w/w). Cumulative respiration and microbial biomass decreased with increasing salinity, but with residue addition they increased with a greater rate in amended sandy soil than in clay soil, with a more pronounced effect for alfalfa than for wheat residue. After 10 days, with wheat residue available N values were 113, 86, and 71 μg in the clay and 144, 114, and 94 μg g^?1 soil in the sand in S1, S2, and S3, respectively. Relative to wheat residue, alfalfa residue increased N availability by 9, 13, and 19% and 22, 24, and 24% in the clay and in the sand in S1, S2, and S3, respectively. Compared to the control, in the clay P availability increased by 33, 57, and 100% with wheat residue and by 58, 128, and 175% with alfalfa residue, whereas in the sand it increased by 92, 45, and 40% with wheat residue and by 130, 145, and 280% with alfalfa residue in S1, S2, and S3, respectively. Availability of N and P increased from day 10 to day 50 in both soils, but with different magnitudes. Residue addition can increase microbial activity and nutrient availability in saline soils, particularly in coarser textured soils.     

Coniferous afforestation increases soil carbon in maritime sand dunes

Afforestation of grasslands can increase C sequestration and provide additional economic and environmental benefits. Pine plantations, however, have often been found to deplete soil organic C and trigger detrimental effects on soils. We examined soil characteristics under a 45-year-old Pinus radiata stand and under adjacent grassland on maritime dunes in temperate Argentina. Soil under the pine plantation had greater soil organic C (+93%), total N (+55%) and available P (+100%) concentrations than under grassland. Carbon was stored under the pinestand at an estimated mean accretion rate of 0.64 Mg ha^?1 y^?1. At 0- to 25-cm depth, soil C amounted to 61 Mg ha^?1 under pine and 27 Mg ha^?1 under grassland. Soil C accumulated more on dune slopes (35 Mg ha^?1 y^?1) than on ridges(29 Mg ha^?1 y^?1) and bottoms (12 Mg ha^?1 y^?1). Compared with the grassland, soil acidity, cation-exchange capacity, base losses (K > Ca = Mg) and C/N ratio increased under pine. Spatial heterogeneity in soil characteristics was greater under pine than under grassland. Such variability was non-systematic and did not support the ‘single-tree influence circle’ concept. Afforestation increased C in soil, forest floor and tree biomass in dunes with ustic climate regime.     

Forest soil chemical changes following fire

Abstract

Prescribed fire to remove residue in a pine plantation on a sandy soil resulted in increases in pH, P, K and Ca in the top 20 cm of soil during the first 15 months following treatment.     

In situ net N transformations in pine,fir, and oak stands of different ages on acid sandy soil, 3 years after liming

Summary The effect of liming on in-situ N transformations was studied in two stands of different ages of each of Scots pine (Pinus sylvestris L.), Douglas fir [Pseudotsuga menziesii (Mirb.) Franco], and common oak (Quercus robur L.). The stands were located on acid sandy soils in an area with high atmospheric N input. The organic matter of the upper 10-cm layer of the soil, including the forest floor, had a relatively high N content (C: N ratio <25) in all stands. Using a sequential core technique, N transformations were measured in both control plots and plots that had been limed 3 years previously with 3 t ha^-1 of dolomitic lime. Limed plots had a higher net NO _inf3 ^sup- production and a higher potential for NO _inf3 ^sup- leaching than the controls in all stands except that of the younger oak. Net N mineralization did not differ significantly between limed and control plots in oak stands and younger coniferous stands but was significantly lower in the limed plots of the older coniferous stands. It is concluded that long-term measurements of net N mineralization in limed forest soils are needed to evaluate the effect of liming with respect to the risk of groundwater pollution.     

Green manure production of Azolla microphylla and Sesbania rostrata and their long-term effects on rice yields and soil fertility

Summary Azolla spp. and Sesbania spp. can be used as green manure crops for wetland rice. A long-term experiment was started in 1985 to determine the effects of organic and urea fertilizers on wetland rice yields and soil fertility. Results of 10 rice croppings are reported. Azolla sp. was grown for 1 month and then incorporated before transplanting the rice and 3–4 weeks after transplanting the rice. Sesbania rostrata was grown for 7–9 weeks and incorporated only before transplanting the rice. Sesbania sp. grew more poorly before dry season rice than before wet season rice. Aeschynomene afraspera, which was used in one dry season rice trial, produced a larger biomass than the Sesbania sp. The quantity of N produced by the Azolla sp. ranged from 70 to 110 kg N ha^-1. The Sesbania sp. produced 55–90 kg N ha^-1 in 46–62 days. Rice grain yield increases in response to the green manure were 1.8–3.9 t ha^-1, similar to or higher than that obtained in response to the application of 60 kg N ha^-1 as urea. Grain production per unit weight of absorbed N was lower in the green manure treatments than in the urea treatment. Without N fertilizer, N uptake by rice decreased as the number of rice crops increased. For similar N recoveries, Sesbania sp. required a lower N concentration than the Azolla sp. did. Continuous application of the green manure increased the organic N content in soil on a dry weight basis, but not on a area basis, because the application of green manure decreased soil bulk density. Residual effects in the grain yield and N uptake of rice after nine rice crops were found with a continuous application of green manure but not urea.     

Boron toxicity of strawberry

Abstract

Radlands Crimson strawberries were grown in a glasshouse with 7 rates of applied boron. Wood shavings mulches with different boron concentrations were also applied as separate treatments. Boron toxicity symptoms were produced in leaves by boron rates of 0.32 kg ha^‐1 and greater on a soil containing 1.6 ug B g^‐1 of hot water extractable boron. Concentrations greater than 123 μg B g^‐1 in old leaves were associated with boron toxicity symptoms.

In the B rate experiment, soil boron concentrations greater than 1.9 μg B g^‐1 soil were associated with leaf toxicity symptoms which increased in severity with increasing soil boron concentrations up to 4.1 μg B g^‐1 soil. Wood shavings mulch containing 17 μg B g^‐1 caused boron toxicity symptoms in older leaves whereas mulches containing less than 6 μg B g^‐1 did not produce toxicity symptoms.     

Fate and interaction with native soil N of ammonium N applied to wetland rice (Oryza sativa L.) grown under saline and non-saline conditions

Summary The effect of salts on the balance of fertilizer N applied as ¹⁵N-labelled ammonium sulphate and its interaction with native soil N was studied in a pot experiment using rice (Oryza sativa L.) as a test crop. The rice crop used 26%–40% of the applied N, the level of applied N and salts showing no significant bearing on the uptake of fertilizer N. Losses of fertilizer N ranged between 54% and 68% and only 5%–8% of the N was immobilized in soil organic matter. Neither the salts nor the rate of N application had any significant effect on fertilizer N immobilization. The effective use of fertilizer N (fertilizer N in grain/fertilizer N in whole plant) was, however, better in the non-saline soil. The uptake of unlabelled N (N mineralized from soil organic matter and that originating from biological N₂ fixation in thes rhizosphere) was inhibited in the presence of the salts. However, in fertilized soil, the uptake of unlabelled N was significantly enhanced, leading to increased A values [(1-% Ndff/% Ndff)x N fertilizer applied, where Ndff is N derived from fertilizer], an index of interaction with the added N. This added N interaction increased with increasing levels of added N. Since the extra unlabelled N taken up by fertilized plants was greater than the fertilizer N immobilized, and the root biomass increased with increasing levels of added N, a greater part of the added N interaction was considered to be real, any contribution by an apparent N interaction (pool substitution or isotopic displacement) to the total calculated N interaction being fairly small. Under saline conditions, for the same level of fertilizer N addition, the added N interaction was lower, and this was attributed to a lower level of microbial activity, including mineralization of native soil N, rootdriven immobilization of applied N, and N₂ fixation.     

Aluminum and nutrient interplay across an age-chronosequence of tea plantations within a hilly red soil farm of subtropical China

Aluminum (Al) and nutrients are key factors to influence tea (Camellia sinensis L.) productivity and quality, while how they interplay in tea plantations under the pressure of global change and increasing fertilization is little studied. In this study, we selected the tea plantations along an age-chronosequence to study Al fractions using a sequential extraction procedure, and nutrient concentrations in topsoil and subsoil and various plant organs. Our results indicated that Al levels and nutrient concentrations in soils and plants generally increased with planting year (P < 0.05), and soil Al bioavailability was positively correlated with Al concentrations in most plant organs. Significant negative relations among pH and most extractable Al fractions in both soil layers suggested that decreased pH would directly alter soil-plant Al cycling due to exogenous nitrogen (N) fertilizer and atmospheric acid deposition. Topsoil total phosphorus (P) was positively correlated with most Al fractions, and root P was positively correlated with root Al concentration, both of which indicate that P and Al were synchronously absorbed by roots in acid tea soils. In addition, topsoil organic carbon was positively correlated with both active and inert Al fractions, indicating that above-ground organic litters would be the main source of elevated Al levels in older tea plantations. Clearly, Al enrichment in tea leaves with increasing planting year needs to be considered under management practices with heavy N and P fertilizers and increasing atmospheric acid deposition in subtropical China.     

Modern forestry vehicles and their impacts on soil physical properties

“Close-to-nature forest stands” are one central key in the project “Future oriented Forest Management” financially supported by the German Ministry for Science and Research (BMBF). The determination of ecological as well as economical consequences of mechanized harvesting procedures during the transformation from pure spruce stands to close-to-nature mixed forest stands is one part of the “Southern Black Forest research cooperation”. Mechanical operations of several typical forest harvesting vehicles were analysed to examine the actual soil stresses and displacements in soil profiles and to reveal the changes in soil physical properties of the forest soils. Soil compaction stresses were determined by Stress State Transducer (SST) and displacement transducer system (DTS) at two depths: 20 and 40 cm. Complete harvesting and trunk logging processes accomplished during brief 9-min operations were observed at time resolutions of 20 readings per second. Maximum vertical stresses for all experiments always exceeded 200 kPa and at soil depths of 20 cm for some vehicles and sequences of harvesting operations approached ≥500 kPa. To evaluate the impacts of soil stresses on soil structure, internal soil strengths were determined by measuring precompression stresses. Precompression stress values of forest soils at the field sites ranged from 20 to 50 kPa at soil depths of 20 cm depth and from 25 to 60 kPa at soil depths of 40 cm, at a pore water pressure of −60 hPa. Data obtained for these measured soil stresses and their natural bearing capacities proved that sustainable wheeling is impossible, irrespective of the vehicle type and the working process. Re-occurring top and subsoil compaction, increases in precompression stress values in the various soil horizons, deep rut depths, vertical and horizontal soil displacements associated with shearing stresses, all affected the mechanical strengths of forest soils. In order to sustain naturally “unwheeled” soil areas with minimal compaction, it is recommended that smaller machines, having less mass, be used to complete forest harvesting in order to prevent or at least to maintain currently minimal-compacted forest soils. Additionally, if larger machines are required, permanent wheel and skid tracks must be established with the goal of their maximum usefulness for future forest operations. A first step towards accomplishing these permanent pathways requires comprehensive planning with the Federal State Baden-Württemberg. The new guideline for final opening with skid tracks (Landesforstverwaltung Baden-Württemberg, 2003) proposes a permanent skid track system with a width of 20–40 m.     

Irrigation with plant extracts in ecofarming increases biomass production and mineral and organic nitrogen content of plants

Seedlings of alfalfa, rape, spinach, and wheat, potted on sandy soil, were irrigated with an aqueous extract of pea shoot (PE, 9.84 g dry weight l^–1) or a solution of Ca, K, Mg, P, and NO₃‐N salts (SS) in a concentration similar to that in PE, for 31–48 days. In comparison to water‐irrigated controls, both SS and PE treated plants showed nearly equal increases in shoot dry weight (29–40 %), whereas PE‐treated plants had higher fresh weights (38–84 %) due to increased succulence. Treatment with SS did not enhance, but sometimes even reduce, the concentrations of Ca, K, Mg, and several trace elements in shoot tissues. In contrast, PE‐treated plants had higher Ca, K, Mg, and organic N, but lower As and Ni contents and were thus of higher nutritive value. Reduced contents of metals in plant tissue correlated with their reduced solubility in the soil solution, which was not due to changes in pH. Fertilizer components such as K and Mg (metals of lower exchange intensity) were incorporated into the soil to release Ca, Sr, and Ba (metals of higher exchange intensity) and reduce the solubility of most trace elements and metal‐complexing humic substances. In addition, application of Ca precipitated heavy metals and humic complexes directly from the soil solution. This effect was partially overcome by PE. Its carboxylic acids could act as phytochelators of metal ions and as mobilizers of the highly diffusible humic substances which carry metals to roots. It is concluded that continuous PE application replaces the quantities of Ca, K, Mg, P, and organic N, but not of NO₃‐N consumed during plant growth. Using PE does not add any relevant quantities of toxic metals to the plant‐soil system.