Some responses of cucumber,grown in beds of peat,to N,K and Mg

Two levels of N and four levels of K, applied to beds of sphagnum peat before planting (Experiment A), were tested in factorial combination with three concentrations of N (50, 175 and 300 mg 1^-1) and two of K (50 and 250 mg T1) in the liquid feed. In three cucumber crops grown, Mg was supplied or omitted before planting as a split plot factor (96 subplots). In two further crops (Experiment B), grown in fresh peat, six concentrations of N (20-320 mg 1^-1) were tested in the liquid feed, all other nutrient levels being constant. In Experiment A, the early yield was reduced by low and high levels of N. The main effect of N on the final yield was not significant, but maximum yield was achieved with 175-300 mg 1^-1 N in the liquid feed where the peat received a small amount of ureaformaldehyde (15 g m“2) and Mg fertilizer. The N x Mg interaction became increasingly marked with successive crops; the loss in yield due to Mg deficiency (<31%) increased with the amount of N applied. K deficiency reduced the yield by up to 66%, and very high levels of K also tended to decrease the yield. The K x Mg interaction became more marked with time and the loss in yield due to Mg deficiency (<23%) increased with the amount of K applied. Leaves from N, K and Mg deficient plants contained <2.5% N, <1.0% K and <0.28% Mg respectively. In Experiment B, where N was supplied only in the liquid feed, the highest yield was obtained at 220 mg 1^-1. The relation between yield and the total amount of N supplied in the feed was defined by a quadratic regression.     

Water status,leaf area and fruit load influence on berry weight and sugar accumulation of cv. ‘Tempranillo’ under semiarid conditions

Berry weight (BW) and sugar concentration (SC) are relevant indices in viticulture since they can be easily measured and, when considered together, give a relatively fair estimation of grape quality. This work aims to evaluate the influence of water availability, leaf area and fruit load on BW and SC, estimating the relative importance of these factors. Leaf area (LA), berry number (BN), yield (YLD), water potential in summer (ψ_pd-s), BW and SC were measured in 16 and 17 ‘Tempranillo’ vineyards in 1999 and 2000, respectively. In all the vineyards, according to local practices, the irrigation amount decreased as summer progressed. The study vineyards comprised a broad range of situations concerning leaf area, fruit load and water status in summer. Average leaf water potential in summer and LA/BN ratio, when considered together, estimated properly BW (R² = 0.91; P < 0.001) and, in a similar way, ψ_pd-s and LA/YLD ratio estimated SC (R² = 0.74; P < 0.001). The relative weight of ψ_pd-s in both relationships was much higher than that of any of the LA:fruit ratios, showing that, under semiarid conditions, water availability plays the main role in regulation of berry growth and sugar accumulation and, therefore, the highest attention should be paid in these areas to irrigation management, seeking the degree of stress that allows optimizing the combination of yield and berry quality in each situation.     

Evaluating variability of root size system and its constitutive traits in hot pepper (Capsicum annum L.) under water stress

The importance of root size system has long been recognized as crucial to cope with drought conditions. This investigation was conducted to: (i) evaluate the variability in root size system of hot pepper at maturity; (ii) estimate the effect of root size system on yield under drought conditions; and (iii) effect of water stress on xylem vessel development and total xylem cross-sectional area in roots of hot pepper cultivars. Twelve diverse hot pepper cultivars were grown in wooden boxes with two different water treatments, normal and in 50% water application as water deficit condition. Mean primary root length (PRL) showed a significant positive correlation with final fruit yield at normal as well as stressed condition. Total dry mass of fruit was reduced by 34.7% in drought treatments (DI) compared to full watered treatment (FI). At harvest, water-stressed plants had 21% lower root dry weight mass but higher root:shoot ratio other than FI. PRL, lateral root density, total xylem area per root cross-section showed a significant positive relationship with fruit yield. Also, lateral root density was higher in cultivars with higher xylem density, particularly in tolerant cultivars. Lateral root density (r = 0.847, P < 0.001) and total xylem cross-sectional area in root (r = 0.926, P < 0.001) were tightly related with total biomass production. The importance of root traits contributing to withstand drought in hot pepper is discussed.     

Regional and maturational effects on essential oils yields and composition of coriander (Coriandrum sativum L.) fruits

The composition of volatile components of the essential oils extracted from fruits of coriander (Coriandrum sativum L.) growing in two different Tunisian regions in both Menzel Temime and Borj El Ifaa was studied by GC and GC–MS. The highest oil yields were observed at final stages of maturity: 0.324 ± 0.09% and 0.327 ± 0.08%, in Menzel Temime and Borj El Ifaa, respectively. Essential oil yields were highly (P < 0.001) affected by the growing region, stages of maturity and their interaction. Essential oil composition changed significantly (P < 0.05) among the different stages of maturity and growing region. Linalool and geranyl acetate were the main compounds at full fruit maturity in the two studied regions. Growing region, stages of maturity and their interaction had a strong effect (P < 0.001) on 35 compounds. α-Pinene, sabinene, limonene, γ-terpinene, cis-dihydrocarvone and geranial were insensible to the regional factor.     

Effect of phosphorus supply on acid phosphatase activity in the leaves of tomato plants

Tomato plants were grown in peat and given either no additional phosphate in the growing-medium or 2.34 kg superphosphate/m³ following an initial growing-period when all plants were adequately supplied with superphosphate. In addition, plants received either 50 or 300 μg N/ml as ammonium nitrate in a liquid feed. Typical symptoms of phosphorus deficiency appeared in the plants only about 6 weeks after transfer to the peat to which no phosphate had been added.Both before and after the onset of symptoms, acid phosphatase activity in extracts from fully expanded leaves of plants in the deficient medium was significantly higher (P < 0.001) than in extracts from plants adequately supplied with superphosphate. Reducing the nitrogen supply did not diminish this biochemical response to phosphorus deficiency. The enzyme assay can be completed within 2 h of receiving the leaf samples and is a rapid biochemical test for phosphorus deficiency in the tomato.     

Mycorrhizal colonization improves onion (Allium cepa L.) yield and water use efficiency under water deficit condition

Most plants benefit from mycorrhizal symbiosis through improvement of water status and nutrient uptake. A factorial experiment with complete randomized blocks design was carried out in greenhouse at Tabriz University, Iran in 2005–2006. Experimental treatments were (a) irrigation interval (7, 9 and 11 days), (b) soil condition (sterile and non-sterile) and (c) arbuscular mycorrhizal fungi (AMF) species (Glomus versiforme, Glomus intraradices, Glomus etunicatum) and non-mycorrhizal (NM) plants as control. Onion (Allium cepa L. cv. Azar-shahr) seeds were sown in sterile nursery and inoculated with fungi species. One nursery left uninoculated as control. Nine weeks old seedlings then were transplanted to the pots. Average pre-irrigation soil water contents reached to about 67, 61.6 and 57.5% of FC corresponding to 7, 9 and 11 days irrigation intervals, respectively. At onion bulb maturity stage (192 days after transplanting), yield, water use efficiency (WUE) and yield response factor (K_y) were determined. The results indicated that AMF colonization increased soil water depletion significantly. G. versiforme under both soil conditions (sterile and non-sterile) and G. etunicatum in sterile soil depleted soil water effectively (P < 0.05). Mycorrhizal fungi improved WUE significantly (P < 0.0001) in both soil conditions. It raised by G. versiforme about 2.4-fold (0.289 g mm⁻¹) in comparison with the control (0.117 g mm⁻¹). G. intraradices and G. etunicatum also had significantly higher WUE than control. Apparently water deficit in 11-day irrigation interval led to lower yield and WUE compared to 9-day interval; the later resulted highest WUE (0.254 g mm⁻¹). Mycorrhizal plants increased seasonal ET significantly due to enhancing in plant growth; G. versiforme in both sterile and non-sterile soil and G. etunicatum in sterile soil had the highest ET. Bulb yield was influenced by irrigation period and fungi species. G. versiforme produced higher yield than other treatments (135.27 g/pot). Mycorrhizal plants in 11-day irrigation interval in spite of suffering from water stress had more bulb yield than non-mycorrhizal plants in all irrigation intervals. Yield in general was higher in 9-day treatments than other irrigating internals significantly (P < 0.05). Onion yield response factor (K_y) was decreased by AMF colonization; implying that symbiosed plants become less responsive to water deficit (longer irrigation interval) compared to the control ones.     

Microbial properties of rhizosphere soils as affected by rotation,grafting, and soil sterilization in intensive vegetable production systems

The increased use of rotation, grafting, and soil sterilization has been documented to increase crop yield in intensive vegetable production systems in China. It is believed that these practices can promote changes in the rhizosphere that enhance early growth of plants. A 2-year greenhouse experiment on tomato double-cropping systems was conducted to investigate the effects of different agricultural treatments on microbial properties of rhizosphere soils and tomato fruit yield. The treatments included planting of welsh onion as a cover crop in the summer fallow (SF) period (CW), rotating vegetable chrysanthemum and tomato (CT), planting graft-tomato instead of auto-root tomato (GT), sterilizing soil with calcium cyanamide in the SF period (TC), and fallowing in the SF period (Control). Microbial population was analyzed by dilution plating. In general, microbial populations were higher in CT, GT and TC than in control. Fungal population was higher in TC whereas a high number of bacteria were found in CT. Soil microbial biomass C and N, total microbial population, organic C and total N showed significant positive correlations (P ≤ 0.01) with each others, and tomato yield showed significant positive correlations (P ≤ 0.05) with organic C, total N and total microbial population. In most treatments, CW, GT and TC significantly (P ≤ 0.05) increased tomato yield by 8%, 21% and 19% in four growing seasons, respectively. CT significantly (P ≤ 0.05) increased tomato yield by 26% in the spring season of 2007. These results suggested that rotation, grafting and soil sterilization could lead to changes in the microbial properties of plant rhizosphere and consequently increase plant yield. Additionally, the responses of plant yield were complex dependent on rhizosphere soil microbes in rotation-, grafting-, and soil sterilization-induced systems.     

Response of evergreen perennial tree crops to gibberellic acid is crop load-dependent: II. GA3 increases yield and fruit size of ‘Hass’ avocado only in the on-crop year of an alternate bearing orchard

Despite problems of low fruit set, small fruit size and alternate bearing, the Hass cultivar dominates commercial avocado production worldwide. To increase yield and fruit size, gibberellic acid (GA₃) (25 mg L⁻¹) was applied at different stages of ‘Hass’ avocado tree phenology: (i) mid–late April (flower abscission), end of June–beginning of July (fruit abscission and beginning of the exponential phase of fruit growth), and mid-January (beginning of pre-harvest fruit drop); (ii) end of June–beginning of July; and (iii) mid-September (near the end of the major fruit abscission period; period of exponential fruit growth). In both years of the research, applications of GA₃ in April and June–July were within the periods of intense flower and fruit abscission, respectively; fruit abscission was low in September and January. Maximum air temperature was not related to flower or fruit abscission. In the on-crop year (391 fruit per untreated control tree), a single application of GA₃ at the end of June–beginning of July significantly increased total yield (kilograms only) and yield of commercially valuable fruit (178–325 g/fruit) (as kilograms and number per tree) compared with the control (P < 0.0001). GA₃ applied in September increased total yield (kilograms only) and yield of commercially valuable fruit (kilograms and number per tree) to values intermediate to and not significantly different from all other treatments, except trees receiving multiple applications of GA₃. This treatment reduced total yield and yield of commercially valuable fruit (kilograms and number per tree) relative to all treatments (P ≤ 0.0002). In contrast, during the off-crop year (32 fruit per control tree), no GA₃ treatment had a significant effect on yield or fruit size compared with the control and all other GA₃ treatments. For ‘Hass’ avocado, there was no negative effect from applying GA₃ at the end of June–beginning of July in both the off- and on-crop years; 2-year cumulative total yield and yield of commercially valuable fruit were increased by 27 kg (128 fruit) and 22 kg (101 fruit) per tree, respectively, above the yield of untreated control trees (P < 0.0001).     

Impact of iron stress on biomass,yield, metabolism and quality of potato (Solanum tuberosum L.)

In order to study the influence of variable iron on biomass, economic yield and role of iron in potato (Solanum tuberosum) cv. Chandramukhi metabolism, plants were grown in refined sand at variable iron ranging from 0.001 to 2.0 mM. Exposure of potato plants to Fe stress (i.e. a Fe concentration different from 0.1 mM) shows retarded growth, decreased chlorophyll concentration and Hill reaction activity, induced changes in enzyme activities and concentration of Fe and Mn. The visible symptoms of iron deficiency appeared on day 15 at 0.001 mM Fe as chlorosis of young leaves. The excess of iron (at >0.1 mM Fe) appeared later, after 25 days and the chlorosis was observed on older leaves. Both deficiency (0.001 mM) and excess (>0.1 mM) of iron reduced the tuber yield, deteriorating its quality by lowering the concentration of sugars, starch and protein nitrogen and increasing the accumulation of non-protein nitrogen and phenols in tubers.     

Hydrangea Ringspot in Britain

The effects of 96 combinations of N, K and Mg were studied in three crops of lettuce grown in peat; there were two sources of N, Nitrochalk (26% N) and sulphur-coated urea (32% N), and molybdenum was included as an extra factor in one crop. The yield and proportion of hearted lettuce increased with applied N until the peat contained 60 mg N I^-1. In two crops higher N concentrations were unfavourable, due to increased acidity in the peat which resulted in greater uptake of Mn by the plants. The yield and the proportions of both hearted and of marketable lettuce declined as the Mn content of the leaves increased. In the third crop, which was not affected by Mn toxicity, there was little response to N over the range 60–250 mg N I^-1. The yield and quality of the produce improved with increasing K until the peat contained 200 mg K I^-1, but concentrations of up to 600 mg K I^-1 had little further effect. The N and K contents of the leaves corresponding to maximum yield were 5% N and 8% K. There was no response to added Mg. The yield and proportion of hearted lettuce were increased by the addition of Mo in plots receiving the heaviest dressing of Nitrochalk. The increase in the proportion of hearted lettuce was greatest in plots also receiving sulphur-coated urea. The water-soluble phosphate content of the peat increased from 19 mg P I^-1 to >50 mg P I^-1 as the pH of the peat declined from 6–7 to 5.5 in response to increasing N application rates.     

The Effects of Nitrogen,Potassium and Sub-Irrigation on the Yield,Quality and Composition of Single-Truss Tomatoes

The effects of nitrogen and potassium on the growth of single-truss tomatoes and on the yield and quality of the fruit have been examined. Two successive crops of cv. Minicraigella were grown with sub-irrigation in a tiered-trough system, the troughs containing a 7:3:2 mixture of loam, peat and grit. Four concentrations of nitrogen in solution (100, 150, 200 and 250 ppm N) were tested in factorial combination with three concentrations of potassium (200, 300 and 400 ppm K), the treatments being replicated four times.

Plant height and leaf length increased markedly with N concentration, as also did the numbers of flowers and marketable fruits per plant, the mean weight per fruit and the total yield. Low N levels delayed harvesting. The proportion of unevenly ripened fruit decreased with increasing concentrations both of N and K. The percentage of hollow fruits was decreased by high K but increased with N concentration.

The titratable acidity of the expressed fruit juices increased significantly with N concentration (P<0.001) but was little affected by K treatment. The N concentration of the nutrient solution also largely controlled the percentage of K in the leaves and the total uptake of this nutrient. These unexpected results were attributed to stimulation of growth by N, leading to increased water requirement and hence to increased application of both N and K by the automatic sub-irrigation system.

The highest yields and best quality fruit were obtained with 250 ppm N and 400 ppm K in the solution, although lower concentrations of K might be preferable after continued cropping in the same compost.     

Effects of cadmium and copper on pollen germination and fruit set in pea (Pisum sativum L.)

In this work, pea (Pisum sativum) plants exposed to increasing cadmium and copper concentrations were tested for heavy metals accumulation in flowers and for ‘in vivo’ pollen germination. Based on the Cd and Cu accumulation amounts in the flowers, an evaluation of the same metals effects on ‘in vitro’ pollen germination was achieved. Moreover, the effects of both metals on fruits number and weight and on seed set and yield at individual plant level were examined. While cadmium concentrations did not affect ‘in vivo’ pollen germination, only higher copper concentrations rendered a significant reduction. This is in contrast with the clear negative effect on pollen germination in vitro and might be explained by the different dynamic and bioavailability of both metals. A clear effect of Cd and Cu was observed on two important yield components ie, fruit weight and seed set. Although results obtained herein cannot give a clear cut relationship between the effect of Ca and Cu on reproductive development and its consequences on yields, they represent emerging results on the potential consequences of metals contamination on reproductive development in plants.     

Effect of different drip irrigation methods and fertilization on growth,physiology and water use of young apple tree

A pot experiment was conducted to investigate the effect of three drip irrigation methods (i.e. conventional drip irrigation (CDI), both sides of the root-zone irrigated with full watering, alternate drip irrigation (ADI), both sides of the root-zone irrigated alternatively with half of the full watering, and fixed drip irrigation (FDI), only one side of the root-zone irrigated with half of the full watering) on growth, physiology, root hydraulic conductance and water use of young apple tree under different nitrogen (N) or phosphorus (P) fertilization (i.e. CK (no fertilization), N₁ (0.2 g N/kg), N₂ (0.4 g N/kg), P₁ (0.2 g P₂O₅/kg) and P₂ (0.4 g P₂O₅/kg)). Results show that compared to CDI, ADI and FDI reduced mean root dry mass, daily transpiration, root hydraulic conductance (K_r), leaf photosynthesis rate, transpiration rate and stomatal conductance of young apple tree by 6.9 and 27.7, 29.3 and 45.0, 6.8 and 37.9, 2.5 and 4.8, 32.6 and 33.0, 22.1 and 22.3%, but increased leaf water use efficiency (WUE) by 31.3 and 29.8%, respectively when they saved irrigation water by 50%. Compared to the CK, N or P fertilization significantly increased K_r, and K_r was increased with the increased N or P fertilization level. There were parabolic correlations between K_r and root dry mass, daily transpiration and stomatal conductance. Our results indicate that ADI reduced transpiration rate significantly, but it did not reduce photosynthesis rate and K_r significantly, thus alternate drip irrigation improved WUE and the regulation ability of water balance in plants.     

Response of evergreen perennial tree crops to gibberellic acid is crop load-dependent. I: GA3 increases the yield of commercially valuable ‘Nules’ Clementine Mandarin fruit only in the off-crop year of an alternate bearing orchard

Worldwide, gibberellic acid (GA₃) is used routinely to increase fruit number and size of seedless mandarins. The efficacy of seven combinations of GA₃ concentrations and application times to maximize total yield and yield of commercially valuable fruit (diameter 57.2–76.2 mm) of ‘Nules’ Clementine mandarin (Citrus reticulata Blanco) was determined in a commercial orchard. GA₃ applied during the period of intense flower abscission failed to reduce the total number of abscised flowers in both the light off- and heavy on-bloom years. No GA₃ treatment reduced fruit abscission when trees were setting the low yield off-crop. However, all trees receiving GA₃ in the high yield on-crop year had fewer abscised fruit than untreated control trees (P = 0.0188) and GA₃ applied 10 days after 75% petal fall and in July increased the number of fruit retained on tagged branches >20% compared to control trees (P = 0.0005). Maximum air temperature was not related to flower or fruit abscission. In the off-crop year (548 fruit per untreated control tree), it was necessary to apply 15 or 25 mg L⁻¹ GA₃ at 60% bloom, 90% bloom, 75% petal fall and 10 days after 75% petal fall to significantly increase the number of fruit per tree and yield of commercially valuable fruit (kilograms and number per tree) (P < 0.0001) above that of control trees, with no reduction in total kilograms per tree. In the following on-crop year, it was better not to apply GA₃: no treatment increased total yield or fruit size and five of seven GA₃ treatments tested reduced total yield as kilograms and number of fruit per tree (P = 0.0003). The results provide strong evidence that GA₃ efficacy is crop load-dependent and dictate that crop load should be considered when using GA₃ to increase fruit set or fruit size of mandarins.     

Phenotypic variations in fruits and selection potential in Sclerocarya birrea subsp. birrea

The domestication of indigenous fruits through agroforestry is seen as one of the important issues in the transformation in the way in which land is used within rural areas. A study of the variation in fruit traits is also important as it is a prerequisite for cultivar development in the domestication process. Following an aridity gradient, phenotypic variation was assessed in fruits of Sclerocarya birrea subsp. birrea, native to West African semi-arid areas. Fruits were collected from 42 trees of various diameters in agroforestry parklands from the dry and semi-humid Sudanian zones. They were partitioned into peel, flesh and pit. Each fruit was labelled and its components were measured and weighted. The overall mean fruit mass was 18.58 ± 0.24 g (mean ± SE) but fruits from the population in the drier zone were significantly larger (19.90 ± 0.37 g vs 17.02 ± 0.24 g; P < 0.001). The results showed a strong correlation between fruits and their components (P < 0.05). Tree diameter was very weakly correlated with fruit traits. There was a high level of variation in fruit characteristics and components within and between populations. The within-population variation accounted for the greatest part (67–100%) of the total variation. Many trees, mainly from the drier zones, showed superior phenotypic traits. Five groups of trees which represented different fruit morphotypes were identified for various prospective exploitations. The results strongly support the implementation of preliminary practical conservation action and domestication of S. birrea in West Africa.     

Effects of plant growth promoting rhizobacteria (PGPR) on yield,growth and nutrient contents in organically growing raspberry

During 2003 and 2005, plant growth promoting effects of two Bacillus strains OSU-142 (N₂-fixing) and M3 (N₂-fixing and phosphate solubilizing) were tested alone or in combinations on organically grown primocane fruiting raspberry (cv. Heritage) plants in terms of yield, growth, nutrient composition of leaves and variation of soil nutrient element composition in the province of Erzurum, Turkey. The results showed that Bacillus M3 treatment stimulated plant growth and resulted in significant yield increase. Inoculation of raspberry plant roots and rhizosphere with M3 and/or OSU-142 + M3, significantly increased yield (33.9% and 74.9%), cane length (13.6% and 15.0%), number of cluster per cane (25.4% and 28.7%) and number of berries per cane (25.1% and 36.0%) compared with the control, respectively. In addition, N, P and Ca contents of raspberry leaves with OSU-142 + M3 treatment, and Fe and Mn contents of the leaves of raspberry with M3 and OSU-142 + M3 applications significantly improved under organic growing conditions. Bacterial applications also significantly effected soil total N, available P, K, Ca, Mg, Fe, Mn, Zn contents and pH. Available P contents in soil was determined to be increased from 1.55 kg P₂O₅/da at the beginning of the study to 2.83 kg P₂O₅/da by OSU-142, to 5.36 kg P₂O₅/da by M3 and to 4.71 kg P₂O₅/da by OSU-142 + M3 treatments. The results of this study suggest that Bacillus M3 alone or in combination with Bacillus OSU-142 have the potential to increase the yield, growth and nutrition of raspberry plant under organic growing conditions.     

Long-term remediation of compacted urban soils by physical fracturing and incorporation of compost

On the Cornell University campus a long-term study has measured the impacts of a soil remediation strategy on plant growth and soil quality using the Cornell Soil Health Test. The Scoop & Dump (S&D) process of soil remediation consists of physically fracturing compacted urban soils, incorporating large quantities (33% by volume) of compost with the use of a backhoe, and annually top dressing with mulch. This study was designed to investigate the impact of this remediation technique for the amelioration of compaction and degradation of soils in the urbanized environment.The study finds that over a 12-year period remediated soils exhibit improved (reduced) bulk density (R² = 0.50) (P < .0001) (n = 30), increased active carbon (R² = 0.61) (P < .0001) (n = 30) and increased potentially mineralizable nitrogen (R² = 0.61) (P < .0001) (n = 30). When S&D soils were compared to unamended (Unam) soils, improvements were found in aggregate stability (S&D = 72.41%, Unam = 34.90%, P < .0001, n = 30), available water holding capacity (S&D = 0.22%, Unam = 0.15%, P < .0001, n = 30), total organic matter (S&D = 8.43%, Unam = 3.23%, P < .0001, n = 30), potentially mineralizable nitrogen (S&D = 27.53 mg/kg, Unam = 3.11 mg/kg, P = 0.0005, n = 30), active carbon (S&D = 1022.47 mg/kg, Unam = 361.60 mg/kg, P < .0001, n = 30), and reduction in bulk density (S&D = 0.89 g/cm³, Unam = 1.47 g/cm³, P < .0001, n = 30). Application of the S&D process provides an alternative to using specified soils and has potential for improving long term soil quality using locally sourced materials and simple methods.     

Steam Pressure in Soil Sterilization: I. In Bins

Responses to three levels of a fritted micronutrient mixture (0, 200 and 500 g m^-3), applied in factorial combination with four rates of liming (average pH values 4.3, 5.1, 6.5 and 7.0), were studied with cvs William Sim and White Sim. In a second experiment, either B or Cu or both nutrients were omitted from the substrate. The 3/1 (v/v) mixture of peat and sand, in raised beds, was cropped for 21 months in both experiments. Flower production was depressed by liming in each experiment and was highest at pH 4.3-5.9. The omission of B from the substrate always resulted in the development of B deficiency symptoms, and <10% of the buds formed failed to develop; the leaves contained 8-11 ppm B. The deficiency reduced flower production and average bloom diameter and increased the incidence of calyx splitting. The omission of Cu had little effect on flower production and quality. Copper deficiency depressed growth slightly and resulted in very low levels of Cu in the leaves (0.9-2.5 ppm), though no specific foliar symptoms were identified. The application of 200 g m^-3 of the fritted micronutrient mixture (253 A) was fully adequate for carnations grown at pH <6.     

Carbon mineralization in the soils under different cover crops and residue management in an intensive protected vegetable cultivation

Continuous cropping under plastic greenhouses, a common practice in intensive Chinese vegetable production systems, has led to the decline of soil productivity and crop yields. A 4-year greenhouse experiment on cucumber double-cropping systems was conducted in Changping country, Beijing, China, to investigate the effects of summer cover crops and residue management on soil microbial biomass carbon (MBC), C mineralization and cucumber yield. The treatments included sweet corn with residue removal after harvest (SR), sweet corn with residue incorporation after harvest (SI), common bean with residue removal after harvest (CR), common bean with residue incorporation after harvest (CI), Garland chrysanthemum and edible amaranth as summer cover crops (GR), and bare fallow during the summer period (Control). The experiment was a randomized complete block design with three replicates. C mineralization was analyzed by trapping the respired CO₂ using air-tight Mason jars containing NaOH vials. After 4 years of the trial, the treatments SR, SI and GR showed significantly (P < 0.05) higher levels of potentially mineralized readily available carbon, C_a (μg CO₂-C g⁻¹), than control. The C_a values for residue retention treatments were significantly related to the biomass inputs for both sweet corn- (r = 0.981; P < 0.01) and common bean-related (r = 0.994; P < 0.01) treatments. Generally, the SI and GR treatments showed greater cumulative C mineralization (CCM) than the other treatments. The relatively low CCM:MBC observed for the SI and GR treatments were significantly (P < 0.05) related to increased cucumber fruit yields from 2005 to 2008. On the contrary, the CR and CI treatments resulted in significant declines in cucumber fruit yields over the same time periods. The responses of cucumber yields to cover crop treatments were related to the dynamics of soil C. These results suggested that the treatments SI and GR could increase C sequestration and improve soil productivity. Further research is required to test how much loss of C (SOC) occurs from the soil due to the protected cultivation using the in situ testing method.