Acid Ultisol Research Articles

Emerging contaminants uptake by an Ultisol and a Vertisol from Puerto Rico

AbstractContaminants of emerging concern (CECs), including pharmaceutical compounds, have been found in irrigation waters and have found their way into crops through the uptake of contaminated water. Many farms in Puerto Rico are irrigated with water that might have considerable levels of CECs. The objective of this study was to determine the quantity of commonly detected CEC adsorbed onto soil particles of two contrasting tropical soils of Puerto Rico (Fraternidad, basic Vertisol [fine, smectitic, isohyperthermic Typic Haplusterts], and Mariana series, acid Ultisol [fine, mixed, active, isohyperthermic Typic Haplohumults]). A CECs single point and multicomponent adsorption experiments were carried out using the batch equilibrium technique. The CECs were naproxen (NPX), O‐desmethylnaproxen (O‐DesNPX), caffeine (CFN), paraxanthine (PX), carbamazepine (CBZ), carbamazepine‐10, 11‐epoxide (Ep‐CBZ), clofibric acid (ClofA), and salicylic acid (SA). The CEC concentrations in water before and after adsorption were determined using a triple quadrupole mass spectroscopy liquid chromatography. The results showed that SA was highly adsorbed by both soils, although in greater concentrations in Fraternidad than Mariana, probably because of greater cation‐bridging. Paraxanthine was adsorbed only in the multicomponent test, probably as a co‐adsorbate. Caffeine, CBZ, and their metabolites were adsorbed in both soils in lesser concentrations than SA and PX. However, NPX and ClofA were not adsorbed by either soil type. Thus, these CECs could potentially move more freely through the soil matrix and reach soil roots in greater quantities than other contaminants.

Physicochemical properties of an acid ultisol subjected to different tillage practices and wood-ash amendment: Impact on heavy metal concentrations in soil and Castor plant

A field experiment was conducted in 2016 and 2017 cropping seasons to determine the effects of tillage practice alone and tillage practices amended with woodash on soil physicochemical properties and soil concentration, shoot and seed uptake of heavy metals (Fe,Zn,Cu,B,Pb). The experiment was laid out as split plot in Randomized Complete Block Design with six treatments and three replications. The treatments were: Flat tillage alone (FO) Mound tillage alone (MO), Ridge tillage alone (RO) Flat tillage +4 t ha-1 woodash, Mound tillage +4 t ha-1 and Ridge tillage +4 t ha-1. Results of the study showed significant (p = 0.05) increase in soil hydraulic conductivity and total porosity (%) in tillage practices relative to woodash amended tillage practices. Results of the study also showed significant (p = 0.05) increase in soil base saturation, organic carbon, available P, soil total N, effective cation exchange capacity, pH and decrease in exchangeable acidity in wood ash amended tillage practices relative to tillage practices alone. Significant (p = 0.05) increases in heavy metals concentration in soil, shoot and seed of castor but to non-toxic level except Fe concentration in soil were observed in tillage practices amended with woodash and tillage practices alone. On the average RW was observed to have the highest improvement in the studied parameters. Use of woodash as soil amendment at applied rate improved soil properties and did not have any negative effect on soil and crops.

Influence of Different Rates of Burnt Rice Husk Dust on Soil Properties and Maize Grain Yield in Acid Ultisol in Abakaliki Southeastern Nigeria

Influence of Different Rates of Burnt Rice Husk Dust on Soil Properties and Maize Grain Yield in Acid Ultisol in Abakaliki Southeastern Nigeria

Amelioration of an acid ultisol by agricultural by‐products

AbstractUltisols are widely distributed in the subtropical regions of China as well as in the world. High acidity of Ultisols limits plant growth and reduces crop yields. Amelioration of an acid Ultisol was investigated by incorporating the residues of canola (Brassica campestris L.), wheat (Triticum aestivum L.), rice (Oryza sativa), corn (Zea mays), soybean (Glycine max), peanut (Arachis hypogaea), faba bean (Vicia faba L.) and pea (Pisum sativum) and Chinese milk vetch (Astragalus sinicus L.) shoots after incubation of the agricultural by‐products for a maximum of 75 days, soil pH was increased by each of the plant materials. The degree of amelioration of the soil acidity by the plant materials was found to depend on the ash alkalinity and N content of the materials; the legumes of higher ash alkalinities and lower N contents, such as peanut straw and faba bean straw, led to the largest increases in soil pH, while the legumes of higher N contents showed less amelioration of the acidity to a certain degree, because of the release of protons during nitrification of NH from mineralisation of organic N. The non‐leguminous materials have medium amelioration effects and increased soil pH by 0·42–0·56 units at the end of incubation. The incorporation of the plant materials also increased exchangeable base status and reduced exchangeable Al, and thus decreased the toxicity of Al in the soil. This study demonstrates that plant materials, especially crop residues, can be used as amendments for acidic soils to restore degraded land in subtropical regions. Copyright © 2010 John Wiley & Sons, Ltd.

Alleviation of soil acidity improves the performance of oil palm progenies planted on an acid Ultisol

Soil acidity is one of the main factors that limit profitable and sustained agricultural production. Oil palm (Elaeis guineensis Jacq.) is mainly planted in acidic soils. In the last years, there has been a stagnated yield and increases in disease incidence and severity worldwide that could be attributed in some extent to soil acidity. This study was conducted to determine the effects of soil acidity alleviation on oil palm seedlings. The effects of ground magnesium limestone or dolomite and magnesium carbonate (0, 1.1, 2.2, 3.3 and 4.4 t ha−1) applied to an Ultisol dominated by kaolinite (pH in water 4.4) were evaluated on selected morphological, physiological and nutritional characteristics of hybrid (Deli dura × AVROS pisifera) and clonal (clone 366) oil palm progenies under nursery conditions for 8 months. Increasing rates of ground magnesium limestone and magnesium carbonate showed a significant effect on improving soil pH and lowering exchangeable aluminium. The hybrid oil palm showed significant either linear or quadratic trends for most of the parameters evaluated, indicating that the best responses for morphological and physiological traits were achieved from 2.5 to 4.23 t ha−1 with ground magnesium limestone and 2.87 to 3.45 t ha−1 with magnesium carbonate. Positive effects of increasing rates of ground magnesium limestone and magnesium carbonate were observed on nitrogen and magnesium uptake. Aluminium concentration in the third frond decreased significantly with increasing ground magnesium limestone rate. A significant reduction of manganese uptake was also observed with increasing rates of both ameliorants. The clonal oil palm progeny exhibited a better performance on un-amended treatment. This may be explained by the significant higher root growth of this progeny. Soil acidity alleviation improved the oil palm seedling growth. These results are important for the oil palm industry and could be applied in the nursery stage as well as extended to the immature stage.

Charcoal Ash and Volatile Matter Effects on Soil Properties and Plant Growth in an Acid Ultisol

There is a growing interest in converting organic wastes to charcoal for use as a sustainable soil amendment with a potential to improve soil productivity and sequester C. Three consecutive greenhouse experiments were conducted to investigate the effects of charcoal with different ash and volatile matter (VM) contents on soil properties and maize (Zea mays) growth and to evaluate the effect of time on charcoal performance. Five charcoal amendments (high-VM corncob, low-VM corncob, Kiawe, Binchotan, and a gasification charcoal of Leucaena leucocephala) applied at a 2.5% (wt/wt) rate were compared with a zero-charcoal control with and without fertilization. Only the gasification charcoal significantly increased maize growth without fertilization. The low-VM corncob charcoal with fertilization significantly increased maize growth by 164% compared with the fertilized control in the first planting cycle. Maize growth in the high-VM corncob charcoal supplemented with fertilizer treatment was significantly lower than that of the fertilizer-alone treatment in the first planting cycle. The negative effect of the high-VM charcoal on the fertilizer was caused by bioavailable carbon in the charcoal, which increased soil microbial activity and could have caused N immobilization. Both the beneficial and detrimental effects of charcoal did not persist beyond the first planting cycle, suggesting that charcoal impacts are temporary. Whereas charcoal ash and VM content seem to be important parameters for predicting charcoal behavior in the short-term, more research is needed to examine a broader spectrum of feedstocks exposed to varying thermal treatments.

Response of maize (Zea mays L.) to different rates of wood-ash application in acid ultisol in Southeast Nigeria

The population densities and distribution of green monkey (Cercopithecus aethiops) at Zugurma sector of Kainji lake national park were investigated. Transects were taken within the vegetation zones. Animal census was carried out by using road count and ground survey between 6.30 - 12.00 h in the mornings and between 15.00 - 18.30 h for six months. Other information recorded were the number of troops, the troop size, and the vegetation where they occurred. Results were pooled together using outer bound method. The diameter at breast height (DBH) and the relative densities of the major plant species in the habitats were also recorded. The result of the study revealed that the habitat of the green monkey have been restricted to the riparian vegetation zone in this sector of the park. The population density in Zugurma sector was 0.6/ km2. The habitats were highly threatened. The average monthly population range was 141 - 795 for the period of study. The troop size was six. The population ratio of male to female was one to two. It was also observed that the juveniles were about 40% of the population. This confirmed that the population is stable and viable. Recommendations were made on the necessary strategies for improvement on the conservation of the species. Key words: Green monkey, population densities, direct count, transects, habitats, troop size.

Amendment of Acid Soils with Crop Residues and Biochars

The liming potential of some crop residues and their biochars on an acid Ultisol was investigated using incubation experiments. Rice hulls showed greater liming potential than rice hull biochar, while soybean and pea straws had less liming potential than their biochars. Due to their higher alkalinity, biochars from legume materials increased soil pH much compared to biochars from non-legume materials. The alkalinity of biochars was a key factor affecting their liming potential, and the greater alkalinity of biochars led to greater reductions in soil acidity. The incorporation of biochars decreased soil exchangeable acidity and increased soil exchangeable base cations and base saturation, thus improving soil fertility.

Nematode infestation and N-effect of legumes on soil and crop yelds in legume-sorghum rotations

The effects of cowpea (Vignaunguiculata) and-groundnut (Arachis hypogea) on succeeding sorghum yields, soil mineral N and nematode infestationwere studied during five cropping seasons (2000 to 2004) in a weakly acid Ultisol of the agronomy research station of Farakô-Ba lo-cated in the Guinean zone of Burkina Faso, West Africa. A factorial 5x5 design of five crop rotations with five fertilizer treatments in a split-plot arrangement with four replications was used.Sorghum yields were affected by the two factors (rotation with legumes and fertilizer ap-plications) during the four years. But interactions were not observed between the two factors. Monocropping of sorghum produced the lowest yields and legume–sorghum rotations increased sorghum yields by50% to 300%. Ground-nut–sorghum and cowpea–sorghum rotations increased soil mineral N by36% and 52%, re-spectively. Crop rotation influenced nematode infestation but the effects on soil and sorghum root infestation differed according to the rotation. The cowpea–sorghum rotation increased soil and sorghum root infestationby nematodes while groundnut–sorghum decree-sed the nematode population. The soil of the cowpea-sorghum rotation contained 1.5 to 2 times more nematodes than the soil of the monocropping of sorghum. In contrast, the soil ofthe groundnut–sorghum rotation contained from 17 to 19 times fewernematodes than that of themonocropping of sorghum. However, nematode infestation did not affect any of the succeeding sorghum yields. It was concluded that the parasitic effect of nematodes was limited by the predominance of positive N-effects on the development of succeeding sorghum.

Dicyandiamide enhances liming potential of two legume materials when incubated with an acid Ultisol

The incorporation of two legume materials increased soil pH, while the nitrification of the ammonium–nitrogen (N) from the ammonification of organic N weakened the liming potential of these materials at the later stages of incubation experiments. The addition of dicyandiamide (DCD) enhanced the liming potential of the two legume materials through its inhibition of nitrification of ammonium-N. At the end of the 60-d incubation, soil pH of the treatment using Chinese milk vetch shoots with DCD was 1.48 units higher than that of control and 1.16 units higher than of the treatment using only Chinese milk vetch. The corresponding data for the pea straw were 1.24 and 1.01 units higher, respectively.

Establishment of the Critical Limit of Soil-Available Phosphorous for Maize Production in Low Acidic Ultisols of West Africa

The relationship between yields and the Bray I–extractable phosphorous (P) was studied on a 21-year-old experiment with maize (Zea mays) in an acid Ultisol of West Africa. Chemical fertilizer alone decreased soil organic carbon and increased soil acidity. The applications of cattle manure maintained the highest level of soil organic carbon, and soil acidity did not decrease. The extractable P varied from 4 mg kg–1 (original soil) to 25 mg P ha–1 in fertilized treatments. A linear correlation (P < 0.01; r = 0.85) was found between soil extractable P and maize yields. Each unit increase in soil extractable P tallied with 16% of yield increase. A critical limit of soil extractable P of 15.6 mg P kg–1 was identified. Below this limit, maize produced less than 2500 kg ha–1, 80% of the maximum yield. Responses to P fertilizer were not expected above this limit.

Effect of rice-husk ash on exchange acidity, growth and yield of groundnut (&lt;i&gt;Arachis hypogaea&lt;/i&gt; l.) in an acid ultisol.

Response of groundnut grown on acidic soil to rice-husk ash applied at 0, 1, 2, 3 and 4 t ha-1 was studied in two field experiments in 2005 and 2006 at Ishiagu in the derived savanna zone of southeast Nigeria. Treatments were fitted in a randomized complete block design (RCBD) replicated three times. Effects of treatments on some soil fertility and productivity parameters were evaluated. The rice-husk ash used contain 64.00 g kg-1Ca, 12.20 g kg-1 Mg, 12.50 g kg-1 P, 9.00 g kg-1 K, 2.10 g kg-1 N, 1.23 g kg-1 organic carbon and had a pH of 10.86. Soil pH increased from initial values of 5.16 to 6.20, while levels of exchangeable acidity correspondingly decreased from initial values of 0.80 to 0.26 cmol kg-1 with 3 t ha-1 applied rice-husk ash. Estimation of linear and quadratic curves respectively for soil pH and exchange acidity show values of r2 = 0.95 for soil pH and R2 = 0.98 for exchange acidity. Significant increases (P < 0.01) in soil P, K and Ca status relate significantly (P = 0.05) to patterns of growth and kernel yield of the crop. The 3 t ha-1 rice-husk ash is recommended. No significant yield advantage was observed at 4 t ha-1.

Peanut response to lime and molybdenum application in low pH soils

Liming acid soils is considered to assure the availability of Mo in crops. Additionally, in peanuts (Arachis hypogaea L.) the positive response to liming is associated to a better supply of Ca+2, Mo for the nitrogenase-complex activity, and other non-nitrogen fixing activities of the crop. This study was thus undertaken to assess the effect of lime, Mo, and the lime-Mo interaction on peanut crop, on an acid Ultisol at the Mococa Experimental Station, Instituto Agronômico, São Paulo State, Brazil, from 1987 to 1990. A randomized complete block design with four replications, in a 4 x 4 factorial arrangement, was used in the study. The factors included four lime rates (0, 2, 4, and 6 t ha-1) broadcast and incorporated into the soil, and Mo (0, 100, 200, and 300 g ha-1) as (NH4)2MoO4 applied as seed dressing. Lime was applied once at the beginning of the study while Mo was applied at every planting. Peanut seed cv 'tatu' was used. Significant increase in peanut kernel yield with liming was only evident in the absence of Mo, whereas the peanut response to Mo was observed in two out of the three harvests. A higher yield response (28 % increase) was found when Mo was applied without liming. Soil molybdenum availability, as indicated by plant leaf analysis, increased significantly when lime was applied. Molybdenum fertilization led to higher leaf N content, which in turn increased peanut yield in treatments with smaller lime doses.

Cadmium availability from granulated and bulk-blended phosphate-potassium fertilizers.

Recent field experiments have shown that high chloride (Cl) in irrigation waters can increase soil cadmium (Cd) uptake by crops because of the formation of soluble ion-pair complexes of Cd with Cl in soil solution. The present study was aimed at testing a hypothesis that KCl in granulated PK fertilizers may enhance Cd uptake by crops from Cd-containing P fertilizers because of close contact between Cd and Cl in the same granules. Less effect would be expected if the same granular PK fertilizers were bulk-blended because of separation of Cd and Cl in different granules. A single superphosphate (SSP) containing 32 mg Cd kg(-1) was granulated by the compaction process with KCl at a P to K ratio = 1:1. Granular KCl was also bulk-blended with granular SSP or Cd-free monocalcium phosphate (MCP) at the same P to K ratio. An acid Ultisol (pH 5.2) was treated with PK fertilizers at 400 mg kg(-1) each for P and K. Upland rice (Oryza sativa L.) and soybean [Glycine max (L.) Merr.] were grown to maturity, and signalgrass (Brachiaria decumbens Stapf.) was cut four times during the study. The results showed that the agronomic effectiveness in increasing crop yield was the same with SSP and MCP whether granulated or bulk-blended with KCl. Concentrations of Cd in plant tissue samples of all crops were much lower for MCP than for SSP. In all the plant tissue samples, except grain samples of upland rice, Cd concentrations obtained with granulated (SSP + KCl) were significantly higher than that with bulk-blended (SSP) + (KCl).

Nutrient recycling potential of Tephrosia candida in cropping systems of southeastern Nigeria

Improving fallow quality in cassava–fallow rotations in southeastern Nigeria through the use of leguminous cover crops has been shown to sustain the productivity of such systems. We studied the effects of age (1 or 2 years) of Tephrosia candida fallow on biomass and nutrient accumulation, on weed biomass and yield response of cassava/maize intercrop and on changes in soil chemical properties in a 3 yr field trial. Results were compared with those obtained in natural fallow. Total biomass and litter were three times higher in plots fallowed for 2 yr with Tephrosia candida than in those under natural fallow for the same period. Weed biomass was 205% lower in T. candida plots fallowed for 2 yr than in the natural fallow and was 174% smaller in T. candida plots fallow for 1 yr than in the natural fallow. Nutrient (nitrogen, phosphorus, calcium, magnesium and potassium) yields in leaves of T. candida fallow for 2 yr were on average 200–300% higher than in leaves of other fallows. The same trend was observed for cassava and maize yields. Soil chemical changes at soil depth 0 to 5 cm showed significant increases in N and C concentrations after 2 yr fallowing and a year of cropping, particularly in the planted fallow plots. Conversely, soil pH, available P and the exchangeable cations, especially Ca were lower, while Al was higher than the initial values, mainly in plots fallowed under T. candida, indicating a tendency of this fallow species to further exacerbate the soil acidification problem of the acid Ultisol at the study site in southeastern Nigeria.

Amending subsoil acidity by surface applications of gypsum, lime, and composts

Crop growth on many highly weathered soils could be severely restricted by the subsoil acidity, which is characterized by low calcium (Ca) and high aluminum (Al) at depths below the plow layer. Since surface applied lime may not improve subsoil conditions, alternatives must be sought. Thus, effects of composts alone or in combination with lime on increasing Ca and decreasing Al in subsoil were evaluated in a simulated soil profile. An acid Ultisol was packed in a 50-cm long column with the top 15 cm being amended with either lime (CaCO3), gypsum (CaSO4·2H2O), a yard waste compost, a bio-solids-based compost (Nitrohumus), or a combination of compost and lime. The column was leached with 40 mL deionized water daily at a rate of 10 mL per 15 min for 27 days (40 cm water). Thereafter, the column was dismantled and cut into 15, 10, 10, 10 cm layers from the top for chemical analysis. Results showed that lime markedly increased pH and reduced exchangeable Al of the surface layer, but had little effect on subsoil pH. Only 7.6% of the applied Ca from lime moved from the applied layer to the next 10-cm layer, while more than 60% of the applied Ca from gypsum moved past the applied layer. Composts effectively reduced exchangeable Al of the top layer, and of the top two layers when applied together with lime. More Ca was found in deeper soil layers when lime and the Nitrohumus compost were applied together than when either material was applied alone. The downward Ca movement was mainly assisted by SO4 2− even in the compost treatments.

Effects of fertilizer and hot-water treatment upon establishment, survival and yield of plantain ( Musa spp., AAB, French)

Plantain ( Musa spp. AAB, French, cv. Essong) was grown on an acid ultisol in southern Cameroon to determine yield response to (1) a hot-water treatment to control nematodes and (2) the application of fertilizer. Observations were made for 42 months. Establishment was unaffected by hot-water treatment or fertilizer. Hot-water treatment reduced nematode infestation to about 30% of that found in untreated plants and increased rhizome survival by 11%. Fertilizer application increased the proportion of bunch-producing plants from 44 to 65% through reduced die-back, toppling and pseudostem breakage during the dry season but had no effect on bunch weight per plant. Fresh bunch yield of the plant-crop was 10.2 Mg ha −1 in unfertilized, untreated, plots; fertilized plots produced 15.3 Mg ha −1 and hot-water treated plots 13 Mg ha −1. Fertilized and hot-water treated plots produced 20.8 Mg ha −1. First ratoon yields were unaffected by fertilizer, but increased due to hot-water treatment from 0.81 to 5.0 Mg ha −1. Plant-crop bunch weight decreased with increasing time between planting and harvest. Mean bunch fresh weight was negatively correlated with an index of root nematode infestation and positively correlated with the number of living roots. For the plant-crop and plant-crop plus ratoon yields, the yield increase due to combined use of fertilizer and hot-water treatment was larger than increases attained by individual measures. Thus combination of hot-water treatment and fertilizer had a synergistic effect on plantain fresh bunch yield, justifying introduction of both measures simultaneously.

Yields of maize/cassava intercrops grown with hedgerows of three multipurpose trees on an acid Ultisol of Cameroon

Maize/cassava were intercropped between hedgerows of Senna spectabilis [(DC.) Irwin and Barneby], Flemingia macrophylla [(Willd.) Merrill] and Dactyladenia barteri [(Hook f ex Oliv.) Engl.] for five consecutive years on an Ultisol in southern Cameroon. Crop yields and hedgerow biomass production in the third to fifth year of cropping are reported. S. spectabilis produced more biomass than F. macrophylla and D. barteri in all years. Cumulative maize grain and cassava tuber yields were highest in F. macrophylla alley cropping, outyielding the no-tree control consistently by 42 to 67% (average 56%). Between hedgerows of D. barteri and S. spectabilis, crops yielded 17% and 16% more than the no-tree control, respectively. However, between S. spectabilis hedgerows, yields were highly variable between years (−15% to +35% compared to the no-tree control) and thus the system is at risk of failure. F. macrophylla is recommended for continuous alley cropping of maize/cassava intercrop. The use of D. barteri may require fallow phases for biomass accumulation followed by cropping phases with rigorous pruning. Although this may lead to lower cumulative yields, the products of the fallow phase, such as stakes and firewood, may provide some compensation.

Longevity of ground magnesium limestone applied to an ultisol

Soils in the upland areas of Malaysia are mostly weathered (Ultisols and Oxisols), having high aluminum (Al), but calcium (Ca) and/or magnesium (Mg) deficient. Magnesium limestone is available in large quantities in Malaysia and is frequently being used to alleviate acidity in the upland soils. This study aimed at assessing the longevity of the limestone applied to an highly weathered acid soil under conditions prevailing in the tropics. The experiment consisted of two phases; in the first phase the plots were treated with various rates of lime, while in the second phase some plots were left as residual treatments. The results of the study showed that an acid Ultisol of Malaysia can be ameliorated by annual limestone application of 11 ha‐1 for maize (Zea mays L.) production. The beneficial effects of liming with ground magnesium limestone (GML) at 41 ha‐1 were observed for about eight years. The critical soil pH and exchangeable Al for maize production were found to be 5 and 0.7 cmolcKg‐1 soil, respectively. The Ca and Mg from the limestone were mostly found in the topsoils because of the increase in cation exchange capacity (CEC) resulting from the pH increase.

Abundance, casting activity, and cast quality of earthworms in an acid Ultisol under alley-cropping in the humid tropics

The density of earthworms, their surface cast production and the composition of surface casts were studied on an acid Ultisol in S.E. Nigeria. Maize and cassava were grown as food crops, continuously or every other year in a maize/fallow rotation, in alley-cropping systems with Flemingia congesta or Dactyladenia barteri as hedgerow trees. Except in the unproductive Flemingia continuous cropping system, > 60 earthworms per square metre were recorded in spite of the low soil pH(H 2O) of 4.1, but biomass was low (approximately 2 g m −2). Surface casts consisted of tubular, up to 3 cm high casts of Pontoscolex corethrurus and some other large earthworm species and small granular casts of Eudrilidae earthworms. The standing mass of casts after 5 months of activity (May–September) ranged between 260 and 570 kg ha −1. Tubular cast production between September and December dropped from 97-18 g m −2 day −1. In spite of the lower biomass than reported in literature for less acid soils, and in light of the low nutrient status of the soil, the estimated amounts of C and nutrients returned to the surface in casts were considerable: 750 kg C, 51 kg N, 16 kg Ca, 2.5 kg Mg and 2 kg K per hectare per year on average.