Olive orchard amended with two experimental olive mill wastes mixtures: effects on soil organic carbon, plant growth and yield

Amendments of olive orchard soil with two different preparations of olive mill solid waste (OMWMs) at the rate of 9tonha(-1) per year for five years in two different plots were compared with an industry standard soil amendment using urea. Both the OMWMs amendments showed significant increases in total organic carbon and humic substances in soil of approximately 40% and 58%, respectively, without negative effects on tree growth and yield. This work has shown that olive oil mill waste (OMW) can be recycled safely using the bioremediation system used in this study. We suggest that this system is particularly beneficial to organic farming and is an alternative solution to direct spreading of raw OMW on farm lands.     

The effects of olive mill waste compost and poultry manure on the availability and plant uptake of nutrients in a highly saline soil

The effects of a compost (produced from by-products of the olive oil industry) and a poultry manure on mineral ion solubility and exchangeability in a highly saline agricultural soil (electrical conductivity for a 1:5 soil:water extract=1.85 dS m(-1)) from Murcia (SE Spain) were studied. The organic amendments did not change significantly the soil electrical conductivity or the soluble Na(+), Ca(2+) or Mg(2+). Only soluble K(+) increased, due to the K(+) supplied by the amendments. The cation exchange capacity increased in treated soils, the exchange complex being mainly saturated with Ca(2+), Mg(2+) and K(+). However, Na(+) was not retained in the exchange sites, and the sodium absorption ratio remained low. The compost and manure increased markedly the shoot growth of the salt-tolerant Beta maritima L. (sea beet) and Beta vulgaris L. (sugar beet). For B. maritima, this seemed to be related to decreases in the shoot concentrations of Na(+) and Cl(-) and increases in K(+) and H(2)PO(4)(-). In the case of B. vulgaris, increases in shoot H(2)PO(4)(-) and B and, for manure-treated soil, a decrease in shoot Na(+) may have been involved. Cultivation of tomato (Lycopersicon esculentum Mill. cv. Moneymaker) in the soil used previously for B. vulgaris indicated that the effects of the manure on tissue cation concentrations were longer-lasting than those of the compost.     

Chemical properties and hydrolytic enzyme activities for the characterisation of two-phase olive mill wastes composting

Two-phase olive mill waste (TPOMW) is a semisolid sludge generated during the extraction of olive oil by the two-phase centrifugation system. Among all the available disposal options, composting is gaining interest as a sustainable strategy to recycle TPOMW for agricultural purposes. The quality of compost for agronomical use depends on the degree of organic matter stabilization, but despite several studies on the topic, there is not a single method available which alone can give a certain indication of compost stability. In addition, information on the biological and biochemical properties, including the enzymatic activity (EA) of compost, is rare. The aim of this work was to investigate the suitability of some enzymatic activities (beta-glucosidase, arylsulphatase, acid-phosphatase, alkaline-phosphatase, urease and fluorescein diacetate hydrolysis (FDA)) as parameters to evaluate organic matter stability during the composting of TPOMW. These enzymatic indices were also compared to conventional stability indices. For this purpose two composting piles were prepared by mixing TPOMW with sheep manure and grape stalks in different proportions, with forced aeration and occasional turnings. The composting of TPOMW followed the common pattern reported previously for this kind of material with a reduction of 40-50% of organic matter, a gradual increase in pH, disappearance of phytotoxicity and formation of humic-like C. All EA increased during composting except acid-phosphatase. Significant correlations were found between EA and some important conventional stability indices indicating that EA can be a simple and reliable tool to determine the degree of stability of TPOMW composts.     

The effects of chronic nitrogen fertilization on alpine tundra soil microbial communities: implications for carbon and nitrogen cycling

Many studies have shown that changes in nitrogen (N) availability affect primary productivity in a variety of terrestrial systems, but less is known about the effects of the changing N cycle on soil organic matter (SOM) decomposition. We used a variety of techniques to examine the effects of chronic N amendments on SOM chemistry and microbial community structure and function in an alpine tundra soil. We collected surface soil (0-5 cm) samples from five control and five long-term N-amended plots established and maintained at the Niwot Ridge Long-term Ecological Research (LTER) site. Samples were bulked by treatment and all analyses were conducted on composite samples. The fungal community shifted in response to N amendments, with a decrease in the relative abundance of basidiomycetes. Bacterial community composition also shifted in the fertilized soil, with increases in the relative abundance of sequences related to the Bacteroidetes and Gemmatimonadetes, and decreases in the relative abundance of the Verrucomicrobia. We did not uncover any bacterial sequences that were closely related to known nitrifiers in either soil, but sequences related to archaeal nitrifiers were found in control soils. The ratio of fungi to bacteria did not change in the N-amended soils, but the ratio of archaea to bacteria dropped from 20% to less than 1% in the N-amended plots. Comparisons of aliphatic and aromatic carbon compounds, two broad categories of soil carbon compounds, revealed no between treatment differences. However, G-lignins were found in higher relative abundance in the fertilized soils, while proteins were detected in lower relative abundance. Finally, the activities of two soil enzymes involved in N cycling changed in response to chronic N amendments. These results suggest that chronic N fertilization induces significant shifts in soil carbon dynamics that correspond to shifts in microbial community structure and function.     

Short-term impact of dry olive mill residue addition to soil on the resident microbiota

The short-term response of the resident soil bacterial and fungal communities to the addition of 5% (w/w) of either dry olive mill residue (DOR), DOR treated with Phlebia sp. (PTDOR) or DOR previously extracted with water (WEDOR) was investigated. As opposed to bacteria, the diversity of fungi increased upon the amendments as assessed by denaturing gradient gel electrophoresis of 18S rDNA. Over the first 30 days, phospholipid fatty acids analyses indicated a gradual decrease in the relative abundances of Gram⁺ bacteria (from 44.8% to 37.9%) and a concomitant increase of Gram⁻ bacteria (from 37.3% to 51.2%) in DOR-amended soil. A considerable increase in the fungal/bacterial ratio was observed after 7 days in DOR, WEDOR and PTDOR-amended soils with respect to the control (0.316, 0.165 and 0.265, respectively, vs. 0.011). The overall microbial activity was stimulated by the amendments as indicated by the higher activity levels of both dehydrogenase and fluorescein diacetate hydrolase. These results indicate that DOR at the application level examined is not toxic on soil microorganisms.     

Two-phase olive mill waste composting: enhancement of the composting rate and compost quality by grape stalks addition

Two-phase olive mill waste (TPOMW) is a semisolid sludge generated by the olive oil industry. Its recycling as a soil amendment, either unprocessed or composted, is being promoted as a beneficial agricultural practice in the Mediterranean area. One of the major difficulties when composting TPOMW is the compaction of the material due to its dough-like texture, which leads to an inadequate aeration. For this reason, the addition of bulking agents is particularly important to attain a proper composting process. In this study we followed the evolution of two composting mixtures (A and B) prepared by mixing equal amounts of TPOMW and sheep litter (SL) (in a dry weight basis). In pile B grape stalks (GS) were added (10% dry weight) as bulking agent to study their effect on the development of the composting process and the final compost quality. The incorporation of grape stalks to the composting mixture changed the organic matter (OM) degradation dynamics and notably reduced the total amount of lixiviates. The evolution of several maturation indices (C/N, germination index, water soluble carbon, humification indices, C/N in the leachates) showed a faster and improved composting process when GS were added. Moreover, chemical (NH₄ ⁺, NO₃ ⁻, cation exchange capacity, macro and micronutrients, heavy metals) and physical properties (bulk and real densities, air content, total water holding capacity, porosity) of the final composts were analysed and confirmed the superior quality of the compost where GS were added.     

Composting of olive leaves and pomace from a three-phase olive mill plant

The composting of olive leaves and olive pomace from a three-phase olive mill was tested as a method for solid waste reuse. The process was carried out using a compost windrow and mixing olive leaves and pomace at a ratio of 1:2. Compost was retained in the windrow for 60 days during which thermophilic temperatures developed for the first 40 days. The compost was then placed into a closed area to mature for another 60 days. The final product proved to be high quality amendment with C/N 27.1 and high nutrient concentrations (N, 1.79%; P, 0.17%; K, 4.97%; Na, 2.8%). Mature compost presented the highest germination index (198%) reported to date, as the germination index in the majority of previous studies is under 80%. Furthermore, tests revealed that addition of 31.5 tons of compost per ha, could increase lettuce yield by 145%.     

Effect of Compost and Manure Soil Amendments on Nematodes and on Yields of Potato and Barley: A 7-Year Study

A 7-year study located in Prince Edward Island, Canada, examined the influence of compost and manure on crop yield and nematode populations. The compost used in this study consisted of cull waste potatoes, sawdust, and beef manure in a 3:3:1 ratio, respectively. No plant-parasitic nematodes were detected in samples collected from windrow compost piles at 5- and 30-cm depths prior to application on field plots. Low population densities of bacterial-feeding nematodes were recovered from compost windrows at the 5-cm depth. Field plots of potato (Solanum tuberosum cv. Kennebec) received compost applied at 16 metric tonnes per hectare, or beef manure applied at 12 metric tonnes per hectare. An adjacent trial with barley (Hordeum vulgare cv. Mic Mac) received only the compost treatment. In both trials the experimental design was a complete randomized block with four replicates. Data averaged over seven growing seasons indicated that population levels of root-lesion nematodes (primarily Pratylenchus penetrans) were higher in root-zone soil in potato plots treated with either compost or manure compared to the untreated control plots. The soil amendments did not affect root-knot nematode (Meloidogyne hapla) population densities in the potato plots, but clover-cyst nematodes (Heterodera trifolii) were more numerous in the root-zone soils of barley treated with compost compared to the untreated plots. Numbers of bacterial-feeding nematodes (primarily Diplogaster lheritieri) were greater in soil in potato plots treated with manure and in soil around barley roots than in untreated plots. Total yields of potato tubers averaged over seven growing seasons increased by 27% in the plots treated with either compost or manure. Grain yields of barley also were increased by 12% when compost was applied. These results indicated that organic amendments increased crop yields, but the impacts on different nematode species varied and usually increased soil population levels.     

Hydrolytic enzyme activities of extracted humic substances during the vermicomposting of a lignocellulosic olive waste

Humic substances and three hydrolytic enzymes (beta-glucosidase, phosphatase and urease) were extracted by neutral sodium pyrophosphate from an olive waste (dry olive cake), alone or mixed with municipal biosolids, during a nine month vermicomposting process. Easily degradable compounds decreased during the vermicomposting process because of microbial consumption. When municipal biosolids were added to dry olive cake, microbial activity increased and the amounts of compounds extracted by pyrophosphate were three times lower than olive cake alone. In both instances, beta-glucosidase, phosphatase and urease activities of the organic extracts either increased or remained the same after a nine month period of vermicomposting, thus suggesting that the humus enzyme complexes resisted microbial and earthworm attack. It is known that humus immobilised enzymes also remain active in soil environments, reactivating the nutrient cycles in soil. The use as amendments of vermicomposted olive cake, alone or when mixed with biosolids, could be a good alternative to reactivate the C, P and N-cycles in degraded soils for regeneration purposes.     

Production of a Metal-Binding Exopolysaccharide by Paenibacillus jamilae Using Two-Phase Olive-Mill Waste as Fermentation Substrate

The present study investigated the use of two-phase olive mill waste (TPOMW) as substrate for the production of exopolysaccharide (EPS) by the endospore-forming bacilli Paenibacillus jamilae. This microorganism was able to grow and produce EPS in aqueous extracts of TPOMW as a unique source of carbon. The effects of substrate concentration and the addition of inorganic nutrients were investigated. Maximal polymer yield in 100-ml batch-culture experiments (2 g l⁻¹) was obtained in cultures prepared with an aqueous extract of 20% TPOMW (w/v). An inhibitory effect was observed on growth and EPS production when TPOMW concentration was increased. Nutrient supplementation (nitrate, phosphate, and other inorganic nutrients) did not increase yield. Finally, an adsorption experiment of Pb (II), Cd (II), Cu (II), Zn (II), Co (II), and Ni (II) by EPS is reported. Lead was preferentially complexed by the polymer, with a maximal uptake of 230 mg/g EPS.     

Molecular microbial and chemical investigation of the bioremediation of two-phase olive mill waste using laboratory-scale bioreactors

Two-phase olive mill waste (TPOMW) is a semi-solid effluent that is rich in contaminating polyphenols and is produced in large amounts by the industry of olive oil production. Laboratory-scale bioreactors were used to investigate the biodegradation of TPOMW by its indigenous microbiota. The effect of nutrient addition (inorganic N and P) and aeration of the bioreactors was studied. Microbial changes were investigated by PCR-temperature time gradient electrophoresis (TTGE) and following the dynamics of polar lipid fatty acids (PLFA). The greatest decrease in the polyphenolic and organic matter contents of bioreactors was concomitant with an increase in the PLFA fungal/bacterial ratio. Amplicon sequences of nuclear ribosomal internal transcribed spacer region (ITS) and16S rDNA allowed identification of fungal and bacterial types, respectively, by comparative DNA sequence analyses. Predominant fungi identified included members of the genera Penicillium, Candida, Geotrichum, Pichia, Cladosporium, and Aschochyta. A total of 14 bacterial genera were detected, with a dominance of organisms that have previously been associated with plant material. Overall, this work highlights that indigenous microbiota within the bioreactors through stimulation of the fungal fraction, is able to degrade the polyphenolic content without the inoculation of specific microorganisms.     

氮磷添加及林分密度对大叶相思林土壤化学性质的影响

大气氮(N)沉降随着人类的活动而日趋严重, 加上中国热带亚热带红壤普遍缺磷(P), 许多森林生态系统由于广泛使用磷肥而产生P富集, 直接影响了森林土壤化学特性。林分密度改变林地的光照、温度、湿度和凋落物持水量, 从而影响土壤特性。为了解外源性N和P添加与林分密度对大叶相思(Acacia auriculiformis)林地土壤化学性质的影响, 为大叶相思人工林的种植密度和土壤养分管理提供科学依据, 该研究于2013到2015年, 以4种不同密度(1 667、2 500、4 444和10 000 trees·hm ^-2)的10年生大叶相思人工林为研究对象, 分别进行添加N、P和N+P处理, 在试验结束时采集0-10 cm土壤, 对其pH、有机质含量、N含量、P含量和钾(K)含量进行了测定分析。结果表明: 施N和N+P均显著降低了土壤的pH和速效K含量, 显著提高了林地土壤的碱解N含量。施N还显著提高了林分土壤的全N含量, 施P显著提高了土壤pH, 降低了林分土壤的全N含量。施P和N+P显著提高了土壤有机质、全P和有效P含量。随着林分密度的增加, 各处理的土壤有机质、全N、碱解N、全P、有效P和速效K含量显著提高。N、P添加处理和密度处理对大叶相思林的土壤pH、有机质和N、P、K含量有显著的交互作用。总体来看, N添加、P添加、林分密度及其交互作用对大叶相思的土壤化学性质有显著影响。     

Land treatment of olive oil mill wastewater

Experiments carried out in lysimeters filled with two calcareous clayey soils (ca 40% CaCO₃; ca 40% clay), showed that a 2m layer of soil almost completely removed the organic and inorganic components of olive oil mill wastewater (OMW) when it was applied in doses of 5000–10000m³ha⁻¹year⁻¹. This efficiency was maintained for at least 2 years. In field experiments, the application of OMW to one of these soils during three successive years at an annual rate of up to 6000m³ha⁻¹ caused changes in some chemical properties of the soil, especially in the upper layer (0–50cm). Concentrations of soil organic matter, Kjeldahl N, soluble NO₃ and available P increased enhancing soil fertility. On the other hand, soil electrical conductivity and sodium adsorption ratio also increased but below the levels representing salinization or sodification hazard for the soil. Furthermore, leaching of Na⁺ and NO₃⁻ below the 1 m layer were detected.     

Assessing the impact of agro-industrial olive wastes in soil water retention: Implications for remediation of degraded soils and water availability for plant growth

Olive solid waste (OSW) is a toxic by-product of olive oil production. Disposal of OSW is a major problem in many Mediterranean countries leading to increased interest in its potential as an organic fertiliser. Relatively little is known regarding the impact of augmentation with OSW and olive solid waste compost (OSWC) on soil hydraulic properties. The effect of OSW and OSWC on the hydraulic characteristics of common agricultural soils with high sand but very different silt and clay contents was analysed. Increased organic inputs induced reductions in soil bulk density and increases in air capacity, hydraulic conductivity and the water content available for plant growth (AWC) in the Sandy Clay Loam (SCL) soil. Similar patterns were observed in Loamy Sand (LS) soil augmented with OSW, but OSWC caused reductions in hydraulic conductivity, air capacity and AWC. Nonetheless, over longer timescales OSWC may benefit the hydraulic properties of loamy sand soils as the compost becomes fully incorporated within the soil structure. Augmentation with organic olive waste induced the hydraulic parameters of the sandy clay loam soil to become identical to those loamy sand (LS) with a higher available water capacity; suggesting that soil augmentation with OSW and OSWC may be an effective tool in remediating and improving degraded or organic poor soils. In terms of the improvement of hydraulic parameters, application rates of 6–8% OSW/OSWC were most beneficial for both soil types.     

Effects of P,K, and liming on soil pH,Al, Mn,K, and forage barley dry matter yield and quality for a newly-cleared Cryorthod

Forage barley dry matter yield and quality, as well as soil pH, Al, and Mn were monitored in response to P, K, and lime application on a newly cleared Typic Cryorthod (Orthid Podzol). The overall yearly yield level was affected by precipitation. Without liming soil acidification occurred after three years of production. The liming rate of 2.2 Mg.ha⁻¹ was found optimal for maintaining initial pH levels (5.66) and increasing forage barley yields. It was also found optimum for K and P utilization for these first years of production. Soil pH dropped an average of 0.33 units over the three years on unlimed P plots and 0.46 units over 4 years on K plots. Phosphorus and K fertilization increased N utilization and resulted in decreased soil acidification. Phosphorus availability was greater in the first year of cropping than in subsequent years, this was likely due to the effects of higher available moisture, liming release of native P, and effects of initial fertilization. There was a 148% increase in total dry matter yield and an 85% increase in protein yield of forage barley with P application. Liming increased total forage barley yields an average of 69% and total protein yields 48%. Reduced barley yields in unlimed plots were due to low soil pH. After two years of cultivation, unlimed plots contained exchangeable Al and soluble Mn levels reported toxic for other soils. The higher liming rates of 4.4 and 6.6 Mg.ha⁻¹ reduced soluble Mn to near critically low levels. soil Al and Mn were highly correlated to pH. Soil exchangeable Al, Mn, and soluble Mn along with tissue Al were inversely correlated to percentage yield. The average yield respone to three levels of applied K, increased from zero initially to 67% by the fourth year. Total dry-matter production increased 32% and total protein yield increased an average of 32% and total protein yield increased an average of 15% with K fertilization over four years. About 60% of the yield response occurred between the 0 and 22kg K.ha⁻¹ rates. Initial soil exchangeable K levels were not maintained even at the highest 66kg K.ha⁻¹ treatment. Soil exchangeable Al and soluble Mn were elevated with dropping pH. Soil K reserves and resupply of exchangeable K in these soils over the long term will be an important factor in crop production.     

Simultaneous Simulations of Uptake in Plants and Leaching to Groundwater of Cadmium and Lead for Arable Land Amended with Compost or Farmyard Manure

The water budget of soil, the uptake in plants and the leaching to groundwater of cadmium (Cd) and lead (Pb) were simulated simultaneously using a physiological plant uptake model and a tipping buckets water and solute transport model for soil. Simulations were compared to results from a ten-year experimental field study, where four organic amendments were applied every second year. Predicted concentrations slightly decreased (Cd) or stagnated (Pb) in control soils, but increased in amended soils by about 10% (Cd) and 6% to 18% (Pb). Estimated plant uptake was lower in amended plots, due to an increase of K_d (dry soil to water partition coefficient). Predicted concentrations in plants were close to measured levels in plant residues (straw), but higher than measured concentrations in grains. Initially, Pb was mainly predicted to deposit from air into plants (82% in 1998); the next years, uptake from soil became dominating (30% from air in 2006), because of decreasing levels in air. For Cd, predicted uptake from air into plants was negligible (1–5%).     

Tropical soils degraded by slash‐and‐burn cultivation can be recultivated when amended with ashes and compost

In many tropical regions, slash‐and‐burn agriculture is considered as a driver of deforestation; the forest is converted into agricultural land by cutting and burning the trees. However, the fields are abandoned after few years because of yield decrease and weed invasion. Consequently, new surfaces are regularly cleared from the primary forest. We propose a reclamation strategy for abandoned fields allowing and sustaining re‐cultivation. In the dry region of south‐western Madagascar, we tested, according to a split‐plot design, an alternative selective slash‐and‐burn cultivation technique coupled with compost amendment on 30–year‐old abandoned fields. Corn plants (Zea mays L.) were grown on four different types of soil amendments: no amendment (control), compost, ashes (as in traditional slash‐and‐burn cultivation), and compost + ashes additions. Furthermore, two tree cover treatments were applied: 0% tree cover (as in traditional slash‐and‐burn cultivation) and 50% tree cover (selective slash‐and‐burn). Both corn growth and soil fertility parameters were monitored during the growing season 2015 up to final harvest. The amendment compost + ashes strongly increased corn yield, which was multiplied by 4–5 in comparison with ashes or compost alone, reaching 1.5 t/ha compared to 0.25 and 0.35 t/ha for ashes and compost, respectively. On control plots, yield was negligible as expected on these degraded soils. Structural equation modeling evidenced that compost and ashes were complementary fertilizing pathways promoting soil fertility through positive effects on soil moisture, pH, organic matter, and microbial activity. Concerning the tree cover treatment, yield was reduced on shaded plots (50% tree cover) compared to sunny plots (0% tree cover) for all soil amendments, except ashes. To conclude, our results provide empirical evidence on the potential of recultivating tropical degraded soils with compost and ashes. This would help mitigating deforestation of the primary forest by increasing lifespan of agricultural lands.     

Does long-term soil warming affect microbial element limitation? A test by short-term assays of microbial growth responses to labile C,N and P additions

Increasing global temperatures have been reported to accelerate soil carbon (C) cycling, but also to promote nitrogen (N) and phosphorus (P) dynamics in terrestrial ecosystems. However, warming can differentially affect ecosystem C, N and P dynamics, potentially intensifying elemental imbalances between soil resources, plants and soil microorganisms. Here, we investigated the effect of long-term soil warming on microbial resource limitation, based on measurements of microbial growth (¹⁸O incorporation into DNA) and respiration after C, N and P amendments. Soil samples were taken from two soil depths (0–10, 10–20 cm) in control and warmed (>14 years warming, +4°C) plots in the Achenkirch soil warming experiment. Soils were amended with combinations of glucose-C, inorganic/organic N and inorganic/organic P in a full factorial design, followed by incubation at their respective mean field temperatures for 24 h. Soil microbes were generally C-limited, exhibiting 1.8-fold to 8.8-fold increases in microbial growth upon C addition. Warming consistently caused soil microorganisms to shift from being predominately C limited to become C-P co-limited. This P limitation possibly was due to increased abiotic P immobilization in warmed soils. Microbes further showed stronger growth stimulation under combined glucose and inorganic nutrient amendments compared to organic nutrient additions. This may be related to a prolonged lag phase in organic N (glucosamine) mineralization and utilization compared to glucose. Soil respiration strongly positively responded to all kinds of glucose-C amendments, while responses of microbial growth were less pronounced in many of these treatments. This highlights that respiration–though easy and cheap to measure—is not a good substitute of growth when assessing microbial element limitation. Overall, we demonstrate a significant shift in microbial element limitation in warmed soils, from C to C-P co-limitation, with strong repercussions on the linkage between soil C, N and P cycles under long-term warming.     

Ammonia volatilization from tropical legume mulches and green manures on unlimed and limed soils

In the humid tropics, legumes are harvested and surface applied as mulch or incorporated as green manure. Studies on N dynamics and budgets from these systems report unaccounted losses of N. Ammonia volatilization may account for a significant percentage of these unexplained N deficits. The main objectives of this study were to: 1) determine the rate and amount of ammonia volatilization from organic amendments, both incorporated (green manure) and unincorporated (mulch), 2) compare ammonia volatilization of organic amendments on both acid (unlimed) and limed soils, and 3) correlate quality, i.e. polyphenolic and lignin concentration and carbon-to-nitrogen ratio, of the organic amendments with ammonia volatilization and net N mineralization. In an incubation experiment, ammonia volatilization losses and net N mineralization were measured from fresh leaflets of 10 legumes over a three-week period. Ammonia volatilization losses for the 10 species ranged from 3.4 to 11.8% of the total N applied in the organic amendment. Lignin content was negatively correlated to ammonia volatilization. Ammonia volatilized from mulches but not green manures, on both unlimed and limed soils, suggesting that ammonia volatilization is a surface phenomenon and not affected by soil pH. Net N mineralization was affected by species and soil pH, but was unaffected by placement (green manure or mulch). For the farmer in low-input agriculture where N tends to be limiting, volatilization losses of N from legume mulch systems could be on the same order of magnitude as crop removal.     

Supplementary foliar N, P and K, applied individually or in combinations, and the tolerance of potatoes to infection by the potato cyst nematodes Globodera rostochiensis and G. pallida

The use of supplementary foliar N, P and K to ameliorate the reduced nutrient uptake of potato plants infected by potato cyst nematode (PCN) were investigated. The potato cv. Pentland Dell achieved yields in plots not treated with oxamyl similar to those found in plots treated with oxamyl when supplementary foliar N or N plus K was applied to plots infested with 13 eggs g^-1 soil of Globodera pallida. Yield improvements from foliar N applications were attributed to increased leaf area index but the reason for yield increases from foliar N plus K applications could not be clarified. In a second experiment, where PCN infestation was 76 eggs g^-l soil, the potato cv. Sante gave yields up to 19% higher than a standard fertiliser practice when supplementary foliar N was applied to plots not treated with oxamyl. Nutrient analysis showed that without oxamyl there were significantly lower concentrations of N, P and K in whole plant dry matter at 58 days after planting (DAP) but higher levels of N in the fourth leaf dry matter at 98 DAP. Emergence was significantly advanced by the use of oxamyl in both experiments. Sante dramatically reduced populations of Globodera rostochiensis from an average of 76 eggs g^-1 soil to 7 eggs g^-1 soil. Foliar application of nutrients is a promising method of ameliorating the effects on potatoes of PCN invasion but the nutrient concentrations and timing of individual sprays need to be more closely matched to crop requirement than was possible in our experiments