Integrated effect of irrigation frequency and phosphorus level on lettuce: P uptake, root growth and yield

The objective of the present research was to assess the effects of fertigation frequency on plant phosphorus and water uptake. Special attention was given to root measurement in order to elucidate the mechanism that relates the fertigation frequency to P uptake and plant growth. Lettuce (Lactuca sativa L., cv. Iceberg) grown in pots filled with quartz sand was chosen as a test plant. The experiment comprised six treatments, with two concentrations of P in irrigation water (0.2 mM and 1.0 mM), and three daily fertigation frequencies (one, four and ten). It was found that high irrigation frequency induced a significant increase in plant-P concentration at low solution-P concentration, whereas at high P concentration the effect of irrigation frequency was insignificant. Increasing the irrigation frequency significantly enhanced the transpiration flux so that the transpiration flux of plants under low irrigation-P level at 10 daily irrigation events was similar to that of plants under high solution-P. The increases with irrigation frequency of P concentration in lettuce organs and of P influx to the roots, at the low P level, were attributed to the elimination of the depletion zone at the root-soil interface by the supply of fresh nutrient solution, and the enhancement of P uptake. The higher P uptake resulted from higher convective flux of dissolved P from the substrate solution to the root surface owing to the higher average moisture content associated with frequent irrigation. The only significant correlation revealed by multiple stepwise regressions relating nutrient concentrations in the plant to yield was that between plant-P concentration and the yield. On the basis of a quadratic regression, 97% of the dry weight variation could be explained by differences in P uptake, indicating that the main effect of fertigation frequency was related to an improvement in P mobilization and uptake. Thus, frequent irrigations may compensate for P shortage.     

High fertigation frequency and phosphorus level: Effects on summer-grown bell pepper growth and blossom-end rot incidence

The objective was to examine the effects of fertigation frequency and P application rate on bell pepper growth and blossom-end rot (BER) incidence, under hot conditions. The experiment comprised six treatments: two concentrations of phosphorus (3 and 30 mg L^–1) combined with three fertigation frequencies (two and eight events per day, and for 1.5 min every 25 min throughout the day). Increasing the fertigation frequency significantly increased the plants acquisition of nutrients, especially phosphorus and manganese. A significant linear regression was obtained between aboveground biomass, and leaf P concentration in the early vegetative stage. Based on the linear regression, 96% of the dry weight variations could be explained by differences in leaf P concentration, indicating that the main effect of fertigation frequency was related to improved P mobilization and uptake. Increasing the daily fertigation frequency from two to eight and to 30 applications reduced the number of BER fruits from 7 to 3 and to 2 per plant, respectively, and accordingly, increased the yield of export-quality fruits from 6.5 to 10 and to 10.5 per plant, respectively. The Mn concentration in plants exposed to low fertigation frequency were low, probably in the deficiency range, but they increased with increasing fertigation frequency. A negative correlation was found between the accumulated number of BER-affected fruits throughout the experiment and fruit-Mn concentrations. In light of recent findings that BER effects in the fruit tissue include the production of oxygen free-radicals and diminution of anti-oxidative compounds and enzymatic activities, and the known crucial role of manganese in enzyme activities and in detoxification of oxygen free-radicals, the relationships between BER incidence and fruit-Mn concentration may indicate that BER is related to Mn deficiency. Future researches are needed to validate this hypothesis.     

Deficit irrigation and fertigation practices in olive growing: Convergences and divergences in two case studies

Abstract

The response of mature olive (Olea europaea L.) trees to both regulated deficit irrigation and fertigation was studied for some consecutive years in sub-humid (Italy) and semi-arid conditions (Spain). All cultivars tested in these experiments were preferentially for table olive consumption (pickling and double-aptitude). Data from these long-term studies on field-grown, mature trees are summarized for assessing common effects of water and nutrient supply on plant behaviour and fruit yield. Seasonal yield variations were observed, and showed that the effect of irrigation treatments was somewhat more gradual in the “on” than in the “off” year. Differences amongst cultivars were always marked. Dry matter accumulation in pulp and pit was positively affected by progressively increasing the amount of water supplied to plants, regardless of years and cultivars. The ratio between pulp and pit fresh weight was negatively affected by irrigation, while fruit size was positively influenced by the gradual increase of irrigation water. Average nitrogen levels in leaves were generally above the deficiency threshold at both experimental plantations. Crop yield was not consistently increased by addition of soil nutrients. The effect of fertigation treatments was relatively uninfluential on oil accumulation in fruits. However, polyphenols in oil samples decreased progressively as the addition of nutrients increased. Critical aspects and strategic decisions in modern olive growing are the selection of cultivar, the supply of water, the option of fertilization, together with other orchard management practices. In this paper we outline various aspects of long-term studies in experimental olive plantations with the aim of highlighting inter-regulatory processes, involving plant growth and crop yield, which must be taken into account when planning future field research and modelling exercises.     

Effect of irrigation frequency and nitrogen on groundnut yield and nutrient uptake

Summary Field experiments were conducted during 1979 and 1980 summer seasons on sandy loam soils of low moisture retentive capacity to study the effect of high frequency irrigation at different levels of N on groundnut yield and nutrient uptake (NPK). Four irrigation frequencies (irrigation at 2, 4, 6 and 8 cm cumulative can evaporation, corresponding to irrigation once in 3, 5, 7 and 10 days respectively) and four levels of nitrogen (0, 20, 40 and 60 kg N/ha) were tested in a factorial randomized block design with three replications. Pod yield of groundnut was maximum (3,293 kg/ha) when irrigations were scheduled at 4 cm cumulative can evaporation (once in 5 days). Addition of N did not increase the pod yield. N and P uptake by the crop was maximum (180 kg N and 18 kg P/ha) with high frequency irrigation of scheduling irrigation at 4 cm cumulative can evaporation. Highest uptake of N (183 kg/ha) and P (19 kg/ha) was with a combination of 20 kg N/ha and high frequency irrigation (4 cm CCE). K uptake was low with low irrigation frequency, while it was highest (67 kg K/ha) at 20 kg N/ha.     

灌溉施肥深度对玉米同化物分配和水分利用效率的影响

 以夏玉米（Zea mays L.）（陕单9号）为供试材料,采用置于遮雨棚下的模拟土柱的方法,进行了不同灌溉施肥深度对夏玉米生长发育、地上与地下部分同化物分配、产量及水分利用效率的影响的试验研究。灌溉施肥深度分4个处理：表面灌施;20 cm 深度灌水施肥;30 cm 深度灌水施肥和40 cm深度灌水施肥。后3个处理为土表下灌施处理。4个重复。试验结果表明：土表下灌施抑制了玉米生育早期的地上部分生长,使根系向土壤中下层的分布加强,从而保证了作物中后期对水分养分的吸收利用,提高了水分利用效率。在本试验条件下,玉     

Effect of different Mg/Ca ratios and electrolyte concentrations in irrigation water on the nutrient content of wheat crop

Summary A study conducted in pots to evaluate the effect of different Mg/Ca ratios (2, 4, 8 and 16) and electrolyte concentrations (20 and 80 meq/l) at SAR 10 in irrigation water on the nutrient uptake and yield of wheat crop in two soils revealed that the average grain and dry matter yields of wheat decreased significantly with an increase in Mg/Ca ratio in irrigation water, but the magnitude of decrease was greater at higher electrolyte concentration than at lower electrolyte concentration. The concentration of Na in both straw and grain of wheat increased and that of K decreased with an increase in Mg/Ca ratio and electrolyte concentration of irrigation water, which led to higher Na/Ca and Na/K ratios in the plant. Further, the concentration of Ca and Mg both in straw as well as in grain increased with increasing electrolyte concentration of the irrigation water. An increasing proportion of Mg in saline irrigation water resulted in decreased concentration of Ca and increased concentration of Mg in both straw and grain of wheat crop. It was also noticed that the increasing proportion of Mg over Ca in the poor quality irrigation water increased the P content of both straw and grain of wheat crop.     

Nutrition and growth of birch and grey alder seedlings in low conductivity solutions and at varied relative rates of nutrient addition

Birch (Betula verrucosa Ehrh.) and grey alder (Alnus incana Moench) seedlings were grown with varied relative addition rates of all nutrients, up to optimum for vegetative growth. The root medium was basically distilled water to which the nutrients, contained in stock solutions in fixed proportions, were added every second hour and in exponentially increased amounts for consumption during the subsequent period. The nutrient weight proportions previously found to be required in birch (100 N:65 K:13 P) were used in all treatments. However, the nutrient proportions required in grey alder were found to be somewhat different (100 N:50 K:18 P). The use of the required proportions in the additions was important for maintenance of maximum growth, efficient nutrient utilization, and low concentrations in the root medium. Luxury consumption and inefficiency occurred at high concentrations. The results show that the nutrient requirements are sufficiently defined, for different relative growth rates, by the nutrient proportions and the relative addition rate. No clear relationships were found between conductivity or concentration in the root medium and the addition rate, net uptake rate, nutrient status, or relative growth rate. The results are in good agreement with data from low concentration and depletion experiments reported in the literature, showing that non-limited uptake rates occur down to very low concentrations. Thus, there is strong evidence that concentration has been incorrectly used when applied as the treatment variable for plant nutrition in plant science and cultivation practice. The dominant factors in sub-optimum and optimum nutrition are the amounts of nutrients available per unit of time, the growth rate, and the nutrient proportions. At low concentration levels, physical factors such as stirring and flow rate of nutrient solution and boundary layer effects are decisive for the rates with which the nutrients become available to the roots. Therefore, at low levels, concentration alone cannot be used as the factor determining nutrient uptake rate. At high levels, concentration is effective as a supra-optimum factor and increased internal percentage contents cause decreased uptake efficiency, thus counter-acting the concentration effect. Nitrogen effects dominated the stress indications when the internal nitrogen percentage content decreased from optimum to the level of the treatments in the beginning of the experiments. Leaf deficiency symptoms disappeared and the root/shoot ratio change ceased when nitrogen status stabilized. Strong linear regressions were found between any two of the variables: relative addition rate of nutrients, relative growth rate, and nutrient status.     

Dry matter production and partitioning in potato plants subjected to combined deficiencies of nitrogen, phosphorus and potassium

Three experiments examined effects on growth, dry matter partitioning and nutrient uptake in potato plants grown in large pots under different combinations of adequate and deficient levels of nitrogen, phosphorus and potassium. N supply affected the growth of all leaves, with low N reducing both the size of individual leaves and the extent of branch growth. P and K availability affected the growth of later formed leaves and only when both were deficient was branch growth substantially reduced. At later stages of growth, total green leaf area was significantly reduced by deficiency of each of the nutrients. Partitioning of dry matter to tubers was markedly reduced by K deficiency and increased in one experiment by P deficiency. When both P and K were deficient, partitioning approximated that under non‐limiting conditions. Leaf weight ratio (LWR) was higher under K deficiency, but not when P was also deficient, and was consistently higher when the ratio of K : P in dry matter was less than approximately five. In these experiments, LWR was not consistently related to shoot N% and N supply had relatively little effect on partitioning. There were large treatment effects on tuber dry matter percentage, characterised by significant interactions especially between N and K. Deficiency of one nutrient increased the concentration of others but uptake was highly regulated as crop content of all three nutrients was reduced when the supply of any one was deficient. The results show that the response of potatoes to single deficiencies may be influenced greatly by the levels of other nutrients.     

Der Einfluss der K-Konzentration der Nährlösung auf die Ertragsbildung,die Qualität und den K-Aufnahmeverlauf bei Hafer

Summary 1. In solution culture with oats (Avena sativa) the effect of the K concentration of the nutrient solution on yield and K uptake rates has been investigated. The K concentration of the different treatments were: 0.1, 0.3, 0.9 and 2.7 me K/l. These concentrations were kept constant during the whole growing period. 2. The growth of the plants in all treatments was normal. Even with the lowest K concentration no visible symptoms of K deficiency occurred. The highest grain yield was obtained with a K concentration of 0.9 me K/l. This yield was about 40% higher than the yield with the lowest K concentration and about 5% higher than the grain yield with the highest K concentration. 3. The increasing K supply had a favorable effect on the fat and crude protein content of the grains. The highest K concentration (2.7 me K/l) resulted in the highest content of crude protein (20%) and of fat (6.2%). 4. The rates of K uptake throughout the growing period differed considerably. The highest rates were measured during the shooting stage and the blossom stage. The K concentration of the nutrient solution influenced the uptake rates significantly. High yields were obtained if the K uptake at the beginning of the blossom stage was higher than 50% of the total K uptake. 5. The optimal K concentration for the yield performance, 0.9 me K/l, found in this experiment cannot be compared with K concentrations of the soil solution under field conditions without reservations. Under field conditions root growth and the contact surface between soil solution and root surface are different. Assuming that under field condition this contact surface nutrient solution/root surface is not larger than in solution culture, also a K concentration of 1 me K/l of the soil solution should meet the K demand of the plants, necessary for the production of high grain yields.      

Diagnosis and Recommendation Integrated System Assessment of the Nutrients Limiting and Nutritional Status of Tomato

Tomato is an important field crop, and nutritional imbalances frequently reduce its yield. Diagnosis and Recommendation Integrated System (DRIS), uses ratios for nutrient deficiency diagnosis instead of absolute concentration in plant tests. In this study, local DRIS norms for the field tomatoes were established and the nutrient(s) limiting tomatoes yield were determined. Tomato leaves were analyzed for nutrients, to identify nutritional status using the DRIS approach. One hundred tomatoes fields were selected from Chatter Plain Khyber Pakhtunkhwa and the Sheikupura Punjab Pakistan. The first fully matured leaf was sampled, rinsed, dried and ground for analyzing P, K, Ca, Mg, Cu, Fe, Mn and Zn using an Inductively Coupled Plasma Atomic Emission Spectrophotometer (ICP AES). Plant tissue N and S were measured by the combustion method. The tomatoes yields were recorded at each location. The data were divided into high-yielding (≥3.79 kg/10 plant) and low-yielding (<3.79 kg/10 plant) populations and norms were computed using standard DRIS procedures. High-yielding plant population had a statistically greater mean S and Fe than the low-yielding population. The average balance index, the sum of functions, for S and Fe were −11.04 and −5.17 which reflected deficiency of S and Fe. Plant nutrients norms established may optimize plant nutrition in field tomatoes for high yield.     

Experimental manipulation of water and nutrient input to a Norway spruce plantation at Klosterhede,Denmark

Water and nutrient supply to forest trees are major factors controlling tree growth and forest vitality. Therefore, changes in the supply of water and nutrients to the trees may be important contributing reasons to the forest damages observed in Europe. Such changes may be caused by several factors, e.g. air pollution, soil acidification and climate change. The present study investigates possible effects on tree growth, growth related parameters and nutrition related to changes in the water and nutrient supply. Water and nutrient supply to the forest soil was manipulated in three roof covered plots. The treatments consisted of 1) summer drought, 2) irrigation and 3) combined irrigation and fertilizer application (fertigation). The results from the roof covered treatment plots were compared to a control plot without roof. Increased supply of water during the spring and early summer increased the diameter growth, whereas application of nutrients in addition to irrigation had no additional effect on tree growth. Addition of nutrients increased the needle content of P, Mn, Ca and Mg. Extended summer drought for 2 months had no effect on the tree growth or other growth parameters, but drought reduced the root development in the upper soil layer. Furthermore, drought induced significant stress symptoms by increasing the cone shredding substantially.     

Effect of potassium on drought resistance of Hibiscus rosa-sinensis cv. Leprechaun: Plant growth,leaf macro- and micronutrient content and root longevity

As competition for the limited water supply available for irrigation of horticultural crops increases, research into crop management practices that enhance drought resistance, plant water-use efficiency and plant growth when water supply is limited has become increasingly essential. This experiment was conducted to determine the effect of potassium (K) nutritional status on the drought resistance of Hibiscus rosa-sinensis L. cv. Leprechaun (Hibiscus). All the treatments were fertilized with Hoagland's nutrient solution, modified to supply K as K₂SO₄, at 0 mM K (K₀), 2.5 mM K (K_2.5), and 10 mM K (K₁₀), under two irrigation regimes (drought stressed [DS] and non-drought stressed [non-DS]). Regular irrigation and fertigation were adopted for 54 days, and drought stress treatment (initiated on day 55) lasted for 21 days; while non-DS control plants continued to receive regular irrigation and fertigation. Following the 21-day drought stress period, plants were labeled with ⁸⁶Rb⁺ to determine the percentage of post-drought stress live roots. Both K deficiency (K₀) and drought stress reduced shoot growth, but drought stress increased root growth and thus the root:shoot ratio. At K₀, plants were K-deficient and had the lowest leaf K, Fe, Mn, Zn, Cu, B, Mo and Al, and highest Ca concentrations. Although the percentage of live roots was decreased by drought stress, K_2.5 and K₁₀ plants (with similar percent live roots) had greater root survival ratio after drought treatment than the K-deficient plants. These observations indicate that adequate K nutrition can improve drought resistance and root longevity in Hibiscus rosa-sinensis.     

Heterogeneous distribution of phosphorus and potassium in soil influences wheat growth and nutrient uptake

Heterogeneous distribution of mineral nutrients in soil profiles is a norm in agricultural lands, but its influence on nutrient uptake and crop growth is poorly documented. In this study, we examined the effects of varying phosphorus (P) and potassium (K) distribution on plant growth and nutrient uptake by wheat (Triticum aestivum L.) grown in a layered or split soil culture in glasshouse conditions. In the layered pot system the upper soil was supplied with P and either kept watered or allowed to dry or left P-deficient but watered, whereas the lower soil was watered and fertilised with K. Greater reductions in shoot growth, root length and dry weight in the upper soil layer occurred in −P/wet than in +P/dry upper soil treatment. Shoot P concentration and total P content were reduced by P deficiency but not by upper soil drying. Genotypic responses showed that K-efficient cv. Nyabing grew better and took up more P and K than K-inefficient cv. Gutha in well-watered condition, but the differences decreased when the upper soil layer was dry. In the split-root system, shoot dry weight and shoot P and K contents were similar when P and K were applied together in one compartment or separated into two compartments. In comparison, root growth was stimulated and plants took up more P and K in the treatment with the two nutrients supplied together compared with the treatment in which the two nutrients were separated. Roots proliferated in the compartment applied with either P or K at the expense of root growth in the adjoining compartment with neither P nor K. Heterogeneous nutrient distribution has a direct decreasing effect on root growth in deficient patches, and nutrient redistribution within the plant is unlikely to meet the demand of roots grown in such patches.     

Nutrient uptake and growth of barley as affected by soil compaction

A field experiment with different levels of compaction was carried out on a mouldboard ploughed silty clay, with the objective of studying the effects on plant nutrient uptake and growth. Soil from the field was also used in laboratory studies of carbon and nitrogen mineralization, and plant uptake of water and nutrients. In the field, low as well as high bulk densities reduced biomass production and nutrient uptake of barley (Hordeum vulgare L.) compared to intermediate bulk densities, where grain yield was approximately 20% higher. In the beginning of the growing season, the concentration of phosphorus and potassium was lowest in plants grown in the loosest and in the most compacted soil, and suboptimal for plant growth. The uptake of nutrients transported by diffusion was more affected by compaction than for nutrients transported by mass flow. The reasons for lowered uptake in loose compared to moderately compacted soil could be reduced root-to-soil contact, a low diffusion coefficient for nutrients and/or reduced mass transport of water to seed and roots. Differences in plant nutrient concentrations between treatments gradually declined until harvest. Immediately after compaction there was probably oxygen deficiency in the compacted soil since the air-filled porosity was critically low, but as the soil dried out, mechanical resistance to root growth may have become a more important growth-limiting factor. In the laboratory study, severe compaction reduced carbon mineralization and uptake of water and nutrients by roots, and caused denitrification. There were only small differences between loose and moderately compacted soil in carbon mineralization, nitrogen concentration in the soil, uptake of water and nutrients and dry matter yield. The large yield increase due to recompaction in the field was not reproduced in the laboratory. Possible reasons are differences in soil temperature between the field and laboratory, in the sowing and fertilizing methods, the pretreatment of the soil and in the spatial variability of bulk density. It is possible that recompaction is needed only in the uppermost part of the soil, which is the loosest, dries out first, and is where the seed as well as the fertilizer are placed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Roots regulate ion transport in the rhizosphere to counteract reduced mobility in dry soil

Diffusion of ions in the soil depends on soil moisture content. In a dry soil, transport of nutrients towards the root and the concomitant uptake could be reduced. However, pot and field experiments showed that this is not always the case. The objective of this paper was to investigate possible mechanisms of plants to counteract reduced nutrient supply due to water shortage. A split root system was used to investigate P and K inflow of oat and sugar beet at different soil moisture contents (Θ) without water shortage for the plant. The measured average P and K inflows were compared to model calculations considering diffusion, mass-flow, sorption and uptake processes. In the calculations, soil dryness impeded diffusion and decreased nutrient inflow as expected. Measured K inflow was decreased in a similar way indicating that Θ influences K diffusion. In contrast to this, measured P inflow was not influenced by Θ and under-estimated by the model. Low and high molecular exudates were collected at different water supply levels showing that exudation rate of both compounds was increased at water shortage. Especially the high molecular exudates (i.e. mainly mucilage) from water-stressed plants increased P concentration in soil solution under dry conditions in an incubation experiment. Calculated inflow considering this increased P concentration agreed well with measured P inflow indicating that exudation of mucilage could be a mechanism to overcome nutrient transport problems due to soil dryness.     

Water and Nutrient Dynamics in Surface Roots and Soils are not Modified by Short-term Flooding of Phreatophytic Plants in a Hyperarid Desert

Little is known of the mechanisms employed by woody plants to acquire key resources such as water and nutrients in hyperarid environments. For phreatophytic plants, deep roots are necessary to access the water table, but given that most nutrients in many desert ecosystems are stored in the upper soil layers, viable shallow roots may be equally necessary for nutrient uptake. We sought to better understand the interaction between water and nutrient uptake from soil horizons differing in the relative abundance of these resources. To this end, we monitored plant water and nutrient status before and after applying flood irrigation to four phreatophytic perennial plant species in the remote hyperarid Taklamakan desert in western China. Sap flow in the roots of five plants of the perennial desert species Alhagi sparsifolia Shap., Karelina caspica (Pall.) Less., Calligonum caput medusea Schrenk, and Eleagnus angustifolia Hill. was monitored using the heat ratio method (HRM). Additionally we measured predawn and midday water potential, foliar nitrate reductase activity (NRA), xylem sap nutrient concentration and the concentration of total solutes in the leaves before, 12 and 96 h after flooding to investigate possible short-term physiological effects on water and nutrient status. Rates of sap flow measured during the day and at night in the absence of transpiration did not change after flooding. Moderately high rates of sap flow (HRM heat pulse velocity, 5–25 cm h⁻¹) detected during the day in soils that had a near zero water content at the surface indicated that all species had contact to groundwater. There was no evidence from sap flow data that plants had utilised flood water to increase maximum rates of transpiration under similar climatic conditions, and there was no evidence of a process to improve the efficiency of water or nutrient uptake, such as hydraulic redistribution (i.e. the passive movement of water from moist soil to very dry soil via roots). Measurements of plant water status, xylem sap nutrient status, foliar NRA and the concentration of osmotically active substances were also unaffected by flood irrigation. Our results clearly show that groundwater acts as the major source of water and nutrients for these plants. The inability of plants to utilise abundant surface soil–water or newly available nutrients following irrigation was attributed to the absence of fine roots in the topsoil layer.     

Combined effects of partial root drying and patchy fertilizer placement on nutrient acquisition and growth of oilseed rape

Partial rootzone drying (PRD) is widely investigated as an effective irrigation technique, resulting in higher water use efficiency and yield for plants growing under mild water deficit. Nutrition is another important factor affecting plant yield, but nutrient acquisition has only rarely been considered in conjunction with PRD. Here we investigate the interaction between water and fertilizer supply in a pot experiment with oilseed rape (Brassica napus L.). Eight treatments were set up for the experiment, a factorial combination of four watering regimes (100% control watering at both sides of the plants; 50% control watering at both sides of the plants; 50% fixed watering applied only to one side of the plants; 50% alternate watering applied alternately to both sides of the plant) and two fertilizer placement levels (uniform over the entire pot, and patchy supplied to one side). For the 50% watering treatments, the total amount of water supplied to the plants was the same, only the pattern of application differed between treatments. Also the total fertilizer applied was the same for all treatments. Oilseed rape roots foraged effectively for water and nutrients resulting in relatively small differences in nutrient uptake and above-ground growth among the water-deficit treatments. Placing fertilizer at one side of the plants increased nutrient uptake, but there were differences between the water treatments and interactions with water uptake. Alternate watering resulted in the highest growth, as a result of the largest nitrogen and phosphorus uptake with the smallest root investment among the three water deficit treatments. Fixed watering resulted in poorest performance when fertilizer was uniformly spread throughout the pot, because the plants were unable to acquire the nutrients on the dry side. Our results show that PRD can be well combined with patchy fertilizer supply, but that reduced nutrient uptake may be expected when nutrients are supplied in parts of the soil volume that remain too dry. Responsible Editor: Yan Li     

A multivariate diagnosis approach applied to celery

Celery (Apium graveolens L. var Dulce) is a high value crop affected at different growth stages by a variety of nutrient disorders. Each nutrient concentration can be corrected for its dependence on concentrations of other nutrients by recognizing plant composition as a closed system whose components add up to one. New variables z _i are computed as logratioed values of individual nutrients, where each nutrient concentration is corrected for the geometric mean of all nutrient concentrations. The z _i are used together with principal component analysis (PCA) to relate celery composition to yield, deficiency symptoms and quality parameters. A survey of commercial celery fields suggested that (1) celery growth is most often limited by P and N deficiencies associated with Fe toxicity; (2) K uptake is most likely to become limiting when the crop reaches 15 cm in height; (3) blackheart incidence can be traced to low levels of K and Mg in external petioles, and (4) cracked stem incidence is related to low B when the crop is 30 cm in height.     

Zinc-biochemical co-fertilization improves rice performance and reduces nutrient surplus under semi-arid environmental conditions

Biofertilizers are a promising approach to substantially improve nutrient recovery and crop production. Moreover, zinc (Zn) deficiency is one of the key abiotic factors limiting global rice production. However, the effect of Zn-biochemical co-fertilization on rice production and nutrients recovery and surplus under semi-arid environmental conditions is not fully obvious. Two years field experiment was conducted to evaluate the effect of Zn-biochemical (nitrogen “N”, phosphorus “P”, and potassium “K”) co-fertilization on yield and yield components, physico-chemical characteristics, and nutrient recovery and surplus as well as farm profitability of four rice (Oryza sativa L.) cultivars treated with two Zn levels (no Zn application, and 600 mg chelated Zn L^?1 as a foliar application) and six fertilization regimes (no fertilizers application, biofertilizers, 25% NPK plus biofertilizers, 50% NPK plus biofertilizers, 75% NPK plus biofertilizers, and 100% NPK). Biofertilizers mixture (cerealin, phosphorine, and potassiomage) were used. The results revealed that chemical constituents, growth attributes, yield, yield components, nutrients uptake (N, P, K, and Zn), and nutrients recovery (N, P, and K) significantly increased due to Zn foliar application. Biofertilizers replacement for 25% of inorganic NPK combined with Zn provides the highest nutrients uptake through increasing N, P, and K recovery by 57–94%, 61–128%, and 45–69%, respectively in the four rice cultivars compared with 100% NPK treatment. This improvement in nutrients uptake and recovery was attributed to decrease nutrients surplus by 64–78%, 46–53%, and 50–59%, respectively. Additionally, Zn-biochemical co-fertilization improves growth attributes, yield, and yield components of rice cultivars through producing more contents of chlorophyll a and b, carotenoids, total carbohydrates, and total amino acids than using 100% NPK alone. All previous characteristics significantly affected by the cultivated rice variety. The net return under the treatment of 75% NPK plus biofertilizers plus Zn foliar application was 21.5–27.5% higher than the treatment of 100% NPK. Therefore, our findings suggest that biofertilizers replacement for 25% of inorganic NPK combined with Zn foliar application supplies a financially attractive choice to substantially enhance nutrient recovery and production of rice, while effectively reducing nutrients loss.     

Degradation of oxadiazon in a bioreactor integrated in the water closed circuit of a plant nursery

Hardy ornamental nursery stock (HONS) use fertigation as a rational supply of nutrients all along the growth cycle of plants. Nevertheless, that frequency of irrigation increases the risks of nutrient and herbicide leaching and subsequent contamination of the waste water. Therefore, systems of water treatment are required in plant nurseries. Pseudomonas fluorescens strain CG5 cells were immobilized on a ceramic support (sepiolite) contained in a 150 l-bioreactor for the biodegradation of the herbicide oxadiazon in the re-circulated leachates. Percolation and inundation operating processes were assayed in the bioreactor. The levels of oxadiazon in water samples were determined by solid phase extraction on C18 columns and gas chromatography with electron capture detection system. Fifty eight percolation cycles resulted in a significant reduction of oxadiazon up to just 5 microg l(-1) at the outlet. Similar herbicide elimination was achieved after two consecutive 68-h inundation periods. In addition, it was found that the nutrient content in the waste water at the bioreactor outlet was sufficient to support an adequate plant growth.