Release Rates of Ammonium‐Nitrogen,Nitrate‐Nitrogen,Phosphorus, Potassium,Magnesium, Iron,and Manganese from Seven Controlled‐Release Fertilizers

Abstract

Samples of seven controlled‐release fertilizers, Nutricote Total 13–13–13, Nutricote Total 18–6–8, Osmocote Plus 15–9–12, Osmocote 13–13–13, Polyon 18–6–12, Polyon 14–14–14, and Plantacote 14–8–15, were placed in leaching columns containing acid‐washed sand. Samples of all leachates were analyzed weekly to determine release rates of ammonium‐nitrogen (N), nitrate‐N, phosphorus (P), potassium (K), magnesium (Mg), manganese (Mn), and iron (Fe). Release rates for P from all products were slower than those for NH₄‐N, NO₃‐N, and K. Release of Mg, Mn, and Fe was very poor, with less than 50% of the total amount of each of these elements ever being released from the prills for some products. Nutricote products released Fe and Mn more effectively than did Osmocote or Plantacote.     

Wirkung der bodenversauerung auf den N‐, P‐, K‐ und Mg‐gehalt junger Sommergerstepflanzen*

Auf 31 Ackerstandorten (Sand bis stark lehmiger Sand) mit sichtbarer Wachstumsminderung von Sommergerste infolge Bodenversauening wurden von geschädigter und gesunder Teilfläche Boden‐ und Pflanzenproben entnommen. Die Böden wurden auf den pH‐Wert (0,1 N KCl), den DL‐löslichen P‐ und K‐Gehalt sowie den Mg‐Gehalt nach Schachtschabel, die Pflanzenproben auf den N‐, P‐, K‐ und Mg‐Gehalt untersucht. Die Sommergerste war sichtbar geschädigt und im Wachstum gemindert, wenn der pH‐Wert des Bodens unter 4,6 lag. Unter den Bedingungen einer starken Bodenversauerung war der N‐, P‐, K‐ und Mg‐Gehalt der geschädigten Pflanzen im Vergleich zu den Vergleichspflanzen bis um 80% reduziert. Der pH‐Wert des Bodens korreliert mit den N‐, P‐ und K‐Gehalten der Pflanzen, jedoch nicht mit dem Mg‐Gehalt. Signifikante Beziehungen zwischen Gehalt im Boden und in der Pflanze liegen bei P, K und Mg vor. Induzierter Mangel, insbesondere an P und K, trägt nach diesen Ergebnissen zur Wachstumsminderung von Sommergerste auf stark versauerten Böden bei.     

Measurement of nitrous oxide emissions from grassland soil using photo‐acoustic infra‐red spectroscopy,long‐path infra‐red spectroscopy,gas chromatography,and continuous flow isotope‐ratio mass spectrometry

Abstract

This study evaluated the performance of photo‐acoustic infra‐red spectroscopy (PAIRS) for measuring nitrous oxide (N₂O) fluxes in the field, in comparison with long‐path infra‐red spectroscopy ('Hawk'), gas chromatography (GC), and continuous flow isotope‐ratio mass spectrometry (CF‐IRMS). The N₂O flux measurements from fertilized and grazed grassland were made simultaneously by the different methods, before and after water application. Before irrigation, mean N₂O fluxes ranged from 3 to 20 g N ha¹ day¹ for the PAIRS and GC measurements, but were undetectable with the Hawk. Within 2 hours of irrigation, mean fluxes increased to 740, 640, and 270 g N ha‘¹day¹, based on GC, PAIRS, and Hawk measurements, respectively. After about 24 hours, irrigation had reached its full effect and N₂O fluxes had increased to 1,050,710, and 410 g N ha¹ day¹. The GC measurements were consistently higher than the PAIRS measurements. However, a second experiment, comparing the PAIRS analyzer with continuous flow isotope‐ratio mass spectrometry (CF‐IRMS), suggested that the former was negatively biased; the PAIRS response was about 33% lower than CF‐IRMS. When the resulting correction factor was applied to the results of the first experiment, there was very good agreement between the PAIRS and GC measurements. The Hawk measurements were lower than PAIRS and GC, but a statistical comparison was not possible, due to the limited number of Hawk measurements that could be made in the windy weather conditions. Windy conditions also resulted in an underestimation of the N₂O flux by PAIRS compared to GC and CF‐IRMS analysis, which could not solely be attributed to a change in the analyzer sensitivity. There was no obvious explanation for this discrepancy and further investigations are needed to resolve this issue.     

Nutrient status of the lowbush blueberry,Lac‐Saint‐Jean area,Québec,Canada

Abstract

The lowbush blueberry (Vaccinium angustifolium Ait.) is an important commercial crop of the Lac‐Saint‐Jean area (Quebec, Canada). The major blueberry fields are located on sandy soils relatively poor in available mineral nutrients. The nutrients originate from a thin organic layer found on the top of these sandy soils. The leaf mineral contents (N, P, K, Mg, Ca, Mn, Fe, Cu, Zn and B) were measured in five blueberry fields during 1984 and 1985. Soil pH and soil available P, K, and Mg were also assessed. The results show that the leaf mineral contents are generally adequate. However, K and Zn might be occasionally deficient when compared to the actual established standards. The available Mg in soil was significantly correlated with the leaf Mg concentration. The data also suggest that the increase of the pH following the burn pruning seems to influence the nutrition of this species.     

Distribution of DTPA‐extractable Fe,Zn, and cu in soil particle‐size fractions

Abstract

To examine the distribution of DTPA‐extractable Fe, Zn, and Cu in clay, silt, and sand fractions; surface soils were collected from cultivated fields of North Dakota, South Dakota, West Virginia, Iowa, Ohio, and Illinois. Clay, silt, and sand fractions were separated after sonic dispersion of soil water suspension and analyzed for DTPA‐extractable Fe, Zn, and Cu. In general, clay had the highest and sand the lowest amount of DTPA‐extractable metals. Consequently, clay had the highest and sand the lowest intensity and capacity factors for these metals since DTPA micronutrient test measures both these factors.     

Potassium,Calcium, and Magnesium Distribution in an Oxisol under Long‐Term Potassium‐Fertilized Apple Orchard

Abstract

Most Brazilian soils do not possess sufficient concentrations of available potassium (K) to produce maximum apple yield. Potassium distribution was evaluated with a depth profile of a Humic Xanthic Hapludox receiving K fertilization in an apple orchard, cv. Gala/MM106, at Vacaria, Rio Grande do Sul, Brazil. Treatments consisted of four rates of annual maintenance K fertilization. After 12 years of cultivation, soil was sampled in eight depth increments. Potassium, calcium (Ca), and magnesium (Mg) contents were extracted by Mehlich I, ion‐exchange resin, and ammonium acetate pH 7.0. Long‐term application of K fertilizer resulted in K accumulation mainly in the 0‐ to 30‐cm surface layer, with low K mobilization to deeper layers. Increasing rates of K fertilizer did not affect soil Mg concentration but induced a lower Ca concentration extracted by Mehlich I, especially in the 0‐ to 20‐cm layer. The estimated K₂O rate for maximum apple yield was 86.5 kg/ha/year.     

Effect of Selenium on Magnesium,Iron, Manganese,Copper, and Zinc Accumulation in Corn Treated by Indole‐3‐acetic Acid

In this work, the relationship among accumulation of selenium, auxin, and some nutrient elements [magnesium (Mg²⁺), iron (Fe³⁺), manganese (Mn²⁺), copper (Cu²⁺), zinc (Zn²⁺)] in tissues of roots, mesocotyls, and leaves of Zea mays L. plants was studied. Seeds of maize were cultivated for 4 days in the darkness at 27 °C on moist filter paper, then the individual seedlings were transferred into an aerated solution containing the macro‐ and microelements and were cultivated in a greenhouse for 12 h in the light and 12 h (12‐h photoperiod) in the dark at 25 °C. The seedlings were exposed to the solution containing sodium hydrogen selenite (NaHSeO₃), indole‐3 acetic acid (IAA), or IAA+NaHSeO₃ for approximately 96 h before chemical analysis. The concentration of IAA in the external medium was 10^?4 mol dm^?3, concentration of selenite (NaHSeO₃) was 10^?6 mol dm^?3, and the pH of the medium was 6.5.

The accumulation of the probed elements in seedlings of maize was measured by inductively coupled plasma optical emission spectroscopy (ICP‐OES). It was determined that the selenite and IAA, present in the external medium of growing plants, changed the uptake and accumulation of some cations in tissues of leaves, mesocotyls, and roots. The change of transport conditions of these nutrient elements is probably one of the first observed symptoms of selenium effects on plants.     

Interrelationships of minerals in soil‐plant‐animal system at Kuti Ranch,Malawi

Abstract

An experiment was conducted in the central region of Malawi to study the relationship of minerals in soil‐plant‐animal systems to enable prediction of mineral status of beef cattle. Soil, forage and tissues (blood, bone and liver biopsy samples) were collected from cows at the same time in February, April, May, October and December for three consecutive years. Brahman x Malawi Zebu cows were supplemented with mono‐ and di‐calcium phosphate, salt and copper (plus cobalt and selenium) boluses.

Bone, liver and serum minerals (calcium, phosphorus, copper and zinc) correlated poorly to specific minerals in either forage or soil. A few minerals could explain more than 16% of their variation in animal tissues. Consequently, it was concluded that correlation coefficients among soil, plant and animal tissues are low or nonexistent. Therefore, until high, significant, reliable and reproducible correlation coefficients are established among soil, plant animal tissues, prediction of mineral status of animals by regression analysis from mineral content of soil or plants is likely to remain imperfect.     

The glycine‐glomus‐rhizobium symbiosis III. Endophyte effects on leaf carbon,nitrogen, and phosphorus nutrition

Soybean plants [Glycine max (L.) Merr.] were grown in pots and inoculated with Rhizobium japonicum and/or Glomus mosseae (Nicol. & Gerd.) Gerd. & Trappe, either at planting or 20 days later. Nitrogen was supplied in the nutrient solution to plants without nitrogen‐fixing bacteria, and P was added to those without the mycorrhizal fungus. At harvest, 50 days after planting, all plants had leaves of similar dry mass. Each root symbiont grew best in the absence of the other. Growth of Glomus reflected the duration of its growing time and the presence and duration of competition from Rhizobium. Nodule weight in the tripartite associations, on the other hand, was inhibited only by the earlier introduction of Glomus.

Dipartite associations and the plants inoculated with both root symbionts at planting had the highest concentration of leaf N, and the lowest was in those inoculated with both organisms at d 20. Leaf P was highest in plants inoculated only with Rhizobium, and lowest in those tripartite associations involving any inoculation at day 20. The low values were presumably a result of the short duration of endophyte‐mediated P uptake before the plants were harvested.

Although there was almost no difference in leaf sugar concentrations, starch concentrations reflected the duration of Glomus growth, and were greatest in those plants that had supported it for the least time. Uninoculated plants contained the least starch, but produced a greater fresh mass of leaf tissue than any of the tripartite symbionts.     

Effect of sulfur and molybdenum levels on growth,nitrate‐assimilation,and nutrient con‐tent of Phalaris

An experiment was conducted with Phalaris aquatica L. cv. Sirolan under hydroponic conditions in the glasshouse at constant temperature of 25°C and natural sunlight. Plants were grown in double pot system with four sulfur and three molybdenum levels along with all the major‐ and micro‐nutrient elements. There was increase in growth, nitrate‐reductase activity and contents of most of the nutrient elements at all levels of sulfur and 1.68 μ/L molybdenum. Molybdenum at 3.36 μg/L level inhibited growth and nitrate‐reductase activity and decreased concentration of nutrient elements in plant. The inhibitory effect of higher level of molybdenum is perhaps mediated through its role in the nitrate‐reductase.     

Factors affecting DTPA‐extractable Zn,Fe, Mn,and Cu from soils

Abstract

Tests were made to determine the effects of grinding, type of extraction vessel, type of shaker, speed of shaking, time of shaking, time of filtering, soil to solution ratio and other variables on DTPA‐extractable Zn, Fe, Mn, and Cu from soils.

Time of grinding, force of grinding, and the quantity of soil being ground greatly affected the amount of extractable Fe. At the lower grinding force, the quantity of soil being ground only slightly affected extractable Fe, but at the higher grinding force, more Fe was extracted from the smaller sized samples especially at the longer grinding period. Extractable Zn was also increased by longer grinding time and greater grinding force, but increases were much less than increases for Fe. Increasing grinding time tended to increase extractable Mn. The effects of grinding on Cu was inconclusive. Increasing the ratio of extractant to soil increased the amount of extractable Fe from soils and tended to increase Zn, Mn, and Cu but to a lesser extent. Both shaker speed and type of extracting vessel affected the ex‐tractability of all nutrients except Cu. Greatest differences between extracting vessels occurred at the lowest shaker speed, while these differences were smaller or disappeared at the higher shaker speeds. The more thorough the mixing of soil and extracting solution, the higher were the levels of extractable Fe and Mn. A reciprocal shaker extracted more Fe and Mn from soils than a rotary shaker. The rate of dissolution of all four nutrients by DTPA was greatest during the first 5 minutes of extraction. There were large and significant correlation coefficients between levels of nutrients extracted after 15 or 30 minutes of shaking and those extracted after 120 minutes. The findings indicate that the levels of micronutrients extracted under one set of conditions can be related to levels extracted under other conditions by use of a simple linear regression equation for each nutrient.

The results of this study demonstrate the importance of standardizing the methods of preparation and extraction of soils used in the DTPA micronutrient soil test. A standard method for soil grinding and extraction is proposed for DTPA soil test.     

Short‐Term Effect of Lime,Phosphorus, and Iron Amendments on Water‐Extractable Lead and Arsenic in Orchard Soils

Abstract

Lead arsenate was extensively used to control insects in apple and plum orchards in the 1900s. Continuous use of lead arsenate resulted in elevated soil levels of lead (Pb) and arsenic (As). There are concerns that As and Pb will become solubilized upon a change in land use. In situ chemical stabilization practices, such as the use of phosphate‐phosphorus (P), have been investigated as a possible method for reducing the solubility, mobility, and potential toxicity of Pb and As in these soils. The objective of this study was to determine the effectiveness of calcium carbonate (lime), P, and iron (Fe) amendments in reducing the solubility of As and Pb in lead‐arsenate‐treated soils over time. Under controlled conditions, two orchard soils, Thurmont loam (Hapludults) and Burch loam (Haploxerolls), were amended with reagent‐grade calcium carbonate (CaCO₃), iron hydroxide [Fe(OH)₃], and potassium phosphate (KH₂PO₄) and incubated for 16 weeks at 26°C. The experimental results suggested that the inorganic P increased competitive sorption between H₂PO₄ ^? and dihydrogen arsenate (H₂AsO₄ ^?), resulting in greater desorption of As in both Thurmont and Burch soils. Therefore, addition of lime, potassium phosphate, and Fe to lead‐arsenate‐contaminated soils could increase the risk of loss of soluble As and Pb from surface soil and potentially increase these metal species in runoff and movement to groundwater.     

Long‐Term Integrated Nutrient Management for Rice‐Based Cropping Pattern: Effect on Growth,Yield, Nutrient Uptake,Nutrient Balance Sheet,and Soil Fertility

Abstract

A 7‐year‐long field trial was conducted on integrated nutrient management for a dry season rice (Boro)–green manure (GM)–wet season rice (T. Aman) cropping system at the Bangladesh Rice Research Institute Farm, Gazipur during 1993–1999. Five packages of inorganic fertilizers, cow dung (CD), and GM dhaincha (Sesbania aculeata) were evaluated for immediate and residual effect on crop productivity, nutrient uptake, soil‐nutrient balance sheet, and soil‐fertility status. Plant height, active tiller production, and grain and straw yields were significantly increased as a result of the application of inorganic fertilizer and organic manure. Usually, the soil‐test‐based (STB) fertilizer doses for a high‐yield goal produced the highest grain yield of 6.39 t ha^?1 (average of 7 years) in Boro rice. Application of CD at the rate of 5 t ha^?1 (oven‐dry basis) once a year at the time of Boro transplanting supplemented 50% of the fertilizer nutrients other than nitrogen (N) in the subsequent crop of the cropping pattern. A positive effect of GM on the yield of T. Aman rice was observed. Following GM, the application of reduced doses of phosphorus (P), potassium (K), sulfur (S), and zinc (Zn) to the second crop (T. Aman) did not reduce yield, indicating the beneficial residual effect of fertilizer applied to the first crop (Boro rice) of the cropping pattern. The comparable yield of T. Aman was also observed with reduced fertilizer dose in CD‐treated plots. The total P, K, and S uptake (kg/ha/yr) in the unfertilized plot under an irrigated rice system gradually decreased over the years. The partial nutrient balance in the unfertilized plot (T₁) was negative for all the nutrients. In the fertilized plots, there was an apparent positive balance of P, S, and Zn but a negative balance of N and K. This study showed that the addition of organic manure (CD, dhaincha) gave more positive balances. In the T_4c treatment at 0–15 cm, the application of chemical fertilizers along with the organic manures increased soil organic carbon by (C) 0.71%. The highest concentration of total N was observed with T_4c followed by T_4d and T_4b, where CD was applied in Boro season and dhaincha GM was incorporated in T. Aman season. The sixfold increase in soil‐available P in T_4b‐, T_4c‐, T_4a‐treated plots was due to the addition of CD. Dhaincha GM with the combination of chemical fertilizer helps to mobilize soil‐available P by 3 to 6 ppm. The highest amount of soil‐available S was found in T_4c‐ and T_4a‐treated plots. It was 2.5 times higher than that of the initial soil. The application of CD and dhaincha GM along with chemical fertilizers not only increased organic C, total N, available P, and available S but also increased exchangeable K, available Zn, available iron (Fe), and available manganese (Mn) in soil.     

Accumulation,partitioning, and assimilation of nitrate in Opuntia ficus‐indica

Nitrate levels and nitrate reductase activity (NRA) of the widely cultivated prickly‐pear Opuntia ficus‐indica were measured for 5‐year‐old orchard plants in the field between flowering and fruit ripening (May‐August) and for rooted cladodes (stem segments) in a glasshouse in pots that were supplied with 0.8,4, or 16 mM nitrate during the early growth of new cladodes (6 weeks). Nitrate levels were much higher in the cladodes than in the fruit peels or the roots; in both cladodes and fruit peels, nitrate levels were higher in the inner water‐storing layer (parenchyma) than in the outer green photosynthetic layer (chlorenchyma). NRA was confined to the cladode chlorenchyma and was higher in new cladodes than in the underlying cladodes. The orchard study suggested that the nitrate accumulated in 2‐ and 3‐year‐old cladodes served as a reserve for the growth of new organs. At the beginning of the reproductive season, such older cladodes had high nitrate levels of 7 mg/g DW in the chlorenchyma and 45 mg/g DW in the parenchyma, which decreased by 72% and 43%, respectively, by the end of the season. The glasshouse experiments indicated that the cladodes were more important for nitrate reduction than the roots, particularly under high external nitrate concentrations.     

50 Jahre organische und mineralische Düngung: Humusgehalte,N‐Ausnutzung und N‐Bilanzen

Nach Umbruch einer Naturwiese wurden während 48 Jahren zehn organische und mineralische Düngungsverfahren geprüft. Der Wechsel von der futterbaulichen zur ackerbaulichen Nutzung hatte bei allen Verfahren ein Absinken des Humusgehaltes von 2,3% auf 1,4–2,1% zur Folge. Bei regelmässiger Stallmistdüngung und bei mineralischer Düngung stabilisierte sich der Humusgehalt nach ca. 35 Jahren auf einem neuen Niveau bei etwa 1,4 bis 1,6%. Bei der Düngung mit Klärschlamm oder Torf stellte sich nach 48 Jahren noch kein neues Gleichgewicht ein. Sowohl die ausreichende mineralische wie auch die organische Düngung förderte die Menge und Aktivität der Bodenmikroorganismen. Die pflanzenbauliche Ausnutzung des Stickstoffs (N) von organischen Düngern betrug während der gesamten Versuchsdauer meist nur 10–30%. Die N‐Ausnutzung mineralischer Dünger dagegen stieg von 20–70% auf 50–80%. Dies gibt einen Hinweis auf ein erhöhtes Umweltgefährdungspotential organischer Dünger. Unter Berücksichtigung der abnehmenden Humusgehalte deuten auch die N‐Bilanzen auf eine erhöhte Umweltgefahrdung organischer Düngung.     

Dry‐Matter and Grain Yield,Nutrient Uptake,and Phosphorus Use‐Efficiency of Lowland Rice as Influenced by Phosphorus Fertilization

Abstract

Phosphorus (P) deficiency is one of the most yield‐limiting factors in lowland acid soils of Brazil. A field experiment was conducted during two consecutive years to determine dry‐matter and grain yield, nutrient uptake, and P‐use efficiency of lowland rice (Oryza sativa L.) grown on an acidic Inceptisol. Phosphorus rates used in the experiment were 0, 131, 262, 393, 524, and 655 kg P ha^?1 applied as broadcast through termophosphate yoorin. Dry‐matter yield of shoot and grain yield were significantly (P<0.01) and quadratically increased with P fertilization. Concentrations (content per unit dry‐weight leaves) of nitrogen (N), P, and magnesium (Mg) were significantly increased in a quadratic fashion with the increasing P rates. However, concentrations of potassium (K), calcium (Ca), zinc (Zn), copper (Cu), and iron (Fe) were not influenced significantly with P fertilization, and Mn concentration was significantly decreased with increasing P rates. Phosphorus use efficiencies (agronomic, physiological, agrophysiological, recovery, and utilization) were decreased with increasing P rates. However, magnitude of decrease varied from efficiency to efficiency.     

Comparative Phytoremediation of Chromium‐Contaminated Soils by Fenugreek,Spinach, and Raya

Abstract

A glasshouse investigation was undertaken to evaluate the natural potential of fenugreek (Trigonella foenumgraecum L.), spinach (Spinacia oleracea L.), and raya (Brassica campestris L.) for cleanup of chromium (Cr)–contaminated silty loam and sandy soils. Four kilograms of soil per treatment in earthen pots was treated with five levels of chromium [0, 1.25, 2.5, 5.0, and 10.0 mg Cr kg^?1 soil through dipotassium chromate (K₂Cr₂O₇], equilibrated for 21 days at field-capacity moisture content, and then fenugreek, spinach, and raya were grown for 60 days after seeding. The concentration of diethylene triamine pentaacetic acid (DTPA)‐extractable Cr increased significantly with increasing rate of Cr application in both soils, but the increase was higher in sandy soil than in silty loam soil. The DTPA‐extractable Cr in both soils decreased after harvesting of crops compared to its concentration in soil before sowing of the crops. The decrease in DTPA‐extractable Cr concentration was highest in soil growing raya and least in the fenugreek‐growing soil. The percent reduction in dry‐matter yield (DMY) with increasing levels of added Cr in comparison to the zero‐Cr control was highest for fenugreek (49 and 52%) followed by spinach (36 and 42%) and lowest for raya (29 and 34%) in silty loam soil and sandy soil, respectively. Also, the percent reduction in mean shoot yield of all crops was higher in sandy soil (41%) compared to silty loam soil (36%), when the rate of applied Cr was increased from 0 to 10 mg Cr kg^?1 soil. The DMY of both shoot and root was highest for raya and lowest for fenugreek. The Cr concentration in fenugreek, spinach, and raya increased with increasing level of added Cr in both soils. The concentration of Cr in both shoot and root was highest in raya, followed by spinach and fenugreek. The overall mean uptake of Cr in shoot was almost four times and in root was about two times higher in raya compared to fenugreek. The findings indicated that family Cruciferae (raya) was most tolerant to Cr toxicity, followed by chenopodiacea (spinach) and Leguminosae (fenugreek). Because raya removed the highest amount of Cr from soil, it could be used for pytoremediation of mildly Cr‐contaminated soils.     

Fractionation of residual cadmium,copper, nickel,lead, and zinc in previously sludge‐amended soil

Abstract

The fractionation of heavy metals in previously sludge‐amended soil is important to evaluate their behavior in the environment in terms of mobility and availability to crop plants. A surface soil that received two types of sludges at two different rates, plus fertilizer only and no treatment (control), having been fallow for nine years, was used in this study. The contents of cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb), and zinc (Zn) fractions in previously sludge‐amended soils were governed by the total content of these metals in the sludges applied and by the rate of sludge application. The contents of these metals were higher for soils that received the Chicago sludge as compared to that receiving the Huntsville sludge. Furthermore, soils that received 20 Mg/ha/yr of sludge for five years generally had higher levels of these metals than those receiving a single dose at the 100 Mg/ha application rate. The percentage of the total content in the water soluble and exchangeable forms was very low (≤1%) regardless of sludge application. The application of sludges tended to reduce the residual fraction and to increase the organic and carbonate fractions. Overall, the predominant forms of the metals in the sludges were as the Cd‐, Ni‐, Pb‐, and Zn‐carbonate and Cu‐organic fractions.     

No‐tillage corn response to placement of fertilizer nitrogen,phosphorus, and potassium

Abstract

Fertilizer placement for corn (Zea mays L.) has been a major concern for no‐tillage production systems. This 3‐yr study (1994 to 1996) evaluated fertilizer phosphorus (P) or potassium (K) rates and placement for no‐tillage corn on farmers’ fields. There were two sites for each experiment involving fertilizer P or K. Treatments consisted ofthe following fertilizer rates: 0,19,and 39 kg P ha^‐1 or 0, 51, and 102 kg K ha^‐I. The fertilizer was broadcast or added as a subsurface band 5 cm beside and 5 cm below the seed at planting. Early plant growth, nutrient concentrations, and grain yields were measured. At the initiation of the study, soil test levels for P and K at the 0–1 5 cm depths ranged from optimum (medium) to very high across sites. Effects of added fertilizer and placement on early plant growth and nutrient concentrations were inconsistent. Added fertilizer had a significant effect on grain yields in two of twelve site‐years. Therefore, on no‐tillage soils with high fertility, nutrient addition, and placement affected early plant growth and nutrient utilization, but had limited effect on grain yield. Consequently, crop responses to the additions of single element P or K fertilizers under no‐tillage practices and high testing soils may not result in grain yield advantages for corn producers in the Northern cornbelt regardless of placement method.     

Spatial variation of soil test phosphorus and potassium,oxalate‐extractable iron and aluminum,phosphorus‐retention index,and organic carbon content in soils of Western Australia

Abstract

Spatial variation of bicarbonate soil test phosphorus (P) and bicarbonate soil test potassium (K) was studied by measuring soil test values for 40 individual soil samples collected from random locations within eight uniform 100 m by 100 m field sites in south‐western Australia. In addition, for five of the sites, spatial variation of the three P sorption indices (ammonium oxalate extractable iron, ammonium oxalate extractable aluminum, and the P retention index) and of organic carbon (C) was measured for 20 individual soils samples. Spatial variation was found to be large, with coefficient of variation (CV) exceeding 20% in most cases, and 50% in some cases. It is therefore essential to collect an adequate number of soil samples from uniform areas in paddocks in order to provide a representative composite sample to measure the soil properties.