The effect of plant material on the relationship between sodium acetate and sodium bicarbonate extractable phosphorus in a Latahco silt loam soil

Abstract

Standardization of the P soil test procedures is desirable; however, both NaOAc and NaHCO₃ are currently used to extract P from soils in the Pacific Northwest region of the USA. The purpose of this study was to determine the relationship between NaOAc and NaHCO₃ extractable P in soils and to evaluate the effect of plant material on this relationship in a northern Idaho soil. The Ap horizon of a Latahco silt loam was used and alfalfa (Medicago sativa), pea (Pisum sativum) and wheat (Triticum aestivum) plant materials were added as amendments at rates of 0%, 1%, 5% and 10% (w/w). The soils were incubated for 20 weeks under controlled conditions. In addition, other parameters studied included soil water potential (‐0.05, ‐0.15 and ‐0.40 MPa), incubation temperature (10, 20 and 30°C and incubation period. P in samples was extracted by NaOAc and NaHCO₃ extractants. A statistically significant linear relationship between NaOAc and NaHCO₃ extractable P was observed (r² = 0.96). In addition, the types of plant residues added to soil differently affected P extraction by the two extractants. The difference between NaOAc and NaHCO₃ extractable P was greatest in the wheat material treatment while alfalfa material resulted in the smallest effect. Sodium acetate extractable P values increased faster than NaHCO₃ extractable P with increasing amendment rate.

A simple regression relationship will allow conversion between NaOAc and NaHCO₃ extractable P in the Latahco soil. Additions of less than 5 mt/ha plant material will have a minimal impact on this relationship.     

Yield,nutrient, and soil sulfur response to ammonium sulfate fertilization of soybean cultivars 1

With the reduction of sulfur levels in high‐analysis nitrogen (N) and phosphorus (P) fertilizers and in atmospheric deposition, sulfur (S) fertilization may become more important, especially with intensive cropping systems. When high clay content is likely to limit root development into the subsoil, low extractable sulfate‐sulfur (SO₄‐S) levels in the topsoil may suggest possible plant response to S fertilization. Even though ammonium sulfate [(NH₄)₂SO₄] is widely used and readily available for plant uptake, field data are limited on the use of (NH₄)2SO₄ as an S source for soybeans [Glycine max (L.) Merr.]. A study was initiated to determine the effect of S fertilization as (NH₄)₂SO₄ on: (i) the yield, seed weight, grain quality, and leaf and whole‐plant nutrient concentrations of four soybean cultivars grown on soils with high clay content subsoils; and (ii) selected soil chemical characteristics. Sulfur rates were 0, 28, 56, and 84 kg/ha, and soybean cultivars were two Maturity Group IV beans, DeSoto and Douglas, and two Maturity Group V beans, Bay and Essex.

The study was conducted on a Parsons silt loam soil (fine, mixed, thermic, Mollic Albaqualf) in 1986 and 1987, and on a Cherokee silt loam (fine, mixed, thermic, Typic Albaqualf) in 1987. Sulfur application did not significantly affect soybean yield or seed protein or oil concentrations. For whole plants, S concentration increased and N:S ratios decreased with increasing S fertilization. Similar trends were found in soybean leaves. Although N:S ratios of both whole plant and leaf tissue were lowered with S fertilization, the values generally were not below 20:1 which is above cited critical levels. Fertilization with (NH₄)₂SO₄ increased the levels of extractable SO₄‐S in the soil, especially in the 15–30 cm depth. The first‐year accumulation of soil SO₄‐S with increasing S fertilization appeared to be more at a site that was lower in organic matter.     

Evaluation of some soil and plant analysis procedures as predictors of the need for sulfur for corn production

Abstract

The objective of this study was to evaluate the usefulness of measures of mineralized sulfur (S), soil sulfate‐sulfur (SO₄‐S), concentration of S in plant tissue, and the N: S ratio in plant tissue as predictors of the need for S in a fertilizer program for corn (Zea mays L.). Data to evaluate the use of plant analysis for S as a predictor were obtained from ten sites where various rates of N and S were applied to corn. Regression analysis was used to relate the S concentration in the ear leaf tissue as well as the N: S ratio in the same tissue to relative yield when the rate of applied N was held constant at a rate of 168 kg/ha. These measures of S in plant tissue were not significantly related to relative yield at sites where there was no response to fertilizer S as well as sites where added S increased yield.

Data from the same sites were used to assess the ability of soil tests to predict the need for fertilizer S. A measurement of extractable SO₄‐S in the surface soil (0–15 cm) was not reliable for predicting the need for S for corn grown on soils with a silt loam texture.

Static incubation techniques were used to evaluate the amount of S mineralized from soil collected from seven sites. The amount of SO₄‐S measured after four and twelve weeks of incubation was curvilinearly related (p <.05) to yield increase from a S fertilizer. Net mineralized S was less than 2.1 and 3.7 ppm SO₄‐S after four and twelve weeks of incubation, respectively, for soils taken from sites where response to fertilizer S was obtained. Data collected in this study indicate that a measure of mineralized S could improve the ability to predict S needs for corn production on soils with a silt loam texture and a low organic matter content.     

Soil chemical properties after long‐term n fertilization of bromegrass: Nitrogen rate

Abstract

Nitrogen (N) fertilizers increase yield and quality of grass forage, and may also alter soil chemical properties. A field experiment was conducted in south‐central Alberta to determine the effect of long‐term application of ammonium nitrate to bromegrass on concentration and downward mobility of soluble NO₃‐N, extractable NH₄‐N, P, Ca, Mg, and K, and total C and N in a Thin Black Chernozemic loam soil. The fertilizer was applied annually in early spring for 16 years at 0 to 336 kg N/ha. There was little accumulation of NO₃‐N in the soil at N rates of 112 kg/ha or less. However, at rates higher than 112 kg N/ha there was accumulation of NO₃‐N in the 15–30 and 30–60 cm layers, but very little in the 90–120 cm depth. The NH₄‐N accumulated in the 0–5 cm layer when the fertilizer was applied at rates between 168 to 280 kg N/ha and in the 5–10 cm layer at N rates exceeding 280 kg/ha. There was a decline in extractable P in soil with N application up to 84 kg N/ha rate, while it increased with high N rates. The increasing amounts of applied N resulted in a decline in extractable soil Ca, Mg and K, and this decrease was more pronounced in the 0–5,5–10,10–15, and 15–30 cm layers for K, 0–5 and 5–10 cm layers for Ca, and 0–5, 5–10, and 10–15 cm layers for Mg. There was a build‐up of total C and N in the surface soil with increasing rate of applied N.     

Responses of residual and recommended N,P, K,S nutrients and crops to six annual soil test-based fertilizer rates and seeding systems

Responses of residual and recommended nitrogen (N), phosphorus (P), potassium (K), sulfur (S) nutrient amounts and crops (yield, emergence, and height) to 0, 60, 100, and 140% soil test-based fertilizer rate applications on the same plots for six years under minimum tillage and direct seeding systems were assessed. Higher fertilizer rates increased residual nitrate (NO₃)-N, extractable K, and sulfate (SO₄)-S amounts after a low crop yield year, particularly NO₃-N, without temporal trend. Increase in residual available P level at higher fertilizer rates showed a positive temporal trend. Lower N, P, and S fertilizer rates were recommended to crops after higher residual NO₃-N, available P, and SO₄-S levels. Crops effectively used the residual nutrients. Compared to 0%, the relative seed yields at 60, 100, and 140% rates increased with years of fertilization. There were no clear responses of measured soil and crop parameters to seeding systems. Testing residual nutrients can optimize fertilizer use and crop yields.     

Effect of extractable zinc,phosphorus, and soil ph on zinc concentrations in leaves of field‐grown corn

Abstract

The variability in corn yield responses to applications of Zn fertilizer appears to be associated with several complex soil and climatic factors that affect the availability of endogenous soil Zn to the crop under specific conditions. Among the soil chemical properties that influence availability of endogenous Zn are soil pH, organic matter content, and extractable P. Over a period of several years, soil and plant analysis data were collected from 54 field experiments, field trials, and diagnostic visits to producer's fields. These data were subjected to multiple regression analysis, resulting in an equation: Zn_leaf = 37.14 + 1.513 Zn_st ‐4.04 pH_st ‐ 1.791 ln(P_st/100) where Zn_st, pH_st, and P_st were 0.1N HC1 extractable soil Zn (kg/ha), 1:1 soil‐water pH, and Bray's 1 extractable soil P (kg/ha), respectively. These factors accounted for 67% of variation in leaf Zn, which was a large portion of the variability in Zn_leaf considering that climatic conditions, management levels, and varietal differences were uncontrolled in most instances. Using the previously published critical level in the leaf opposite and below the ear as 17 μg Zn/g, these data can be used to set required soil test levels of Zn at different levels of extractable P and soil pH. Inadequate levels of extractable Zn would range from 2.5 (at pH 6.0, P = 70 kg/ha) to, 9.5 kg/ha (at pH 7.5, P = 420 kg/ha).     

Accumulation of zinc,phosphorus, and magnesium by navy bean seed

Considerable variation is found in zinc (Zn Concentration in navy bean (Phaseolus vulgaris L.) seed, an important food source of Zn and magnesium (Mg). The influence that phosphorus (P) and Zn fertilizers, and source of nitrogen (N) (inoculation with Rhizobium phaseoli versus 150 mg/kg NH₄NO₃‐N) had on growth and nutrient uptake of ‘Upland’ navy bean was studied under greenhouse conditions on a Glyndon loamy fine sand, a Calciaquoll low in available N, P, and Zn. Yields of stems (+ pod walls), blades, and seed were increased by N, P, and Zn fertilizers. Zinc concentration at maturity varied between 13 and 37 mg/kg for seed, 15 and 39 mg/kg for blades, and 5 and 30 mg/kg for stems. Zinc fertilizer was the chief factor responsible for this variability. Phosphorus concentration at maturity varied between 4.0 and 6.2 g/kg for seed, 1.9 and 11.8 g/kg for blades, and 1.0 to 2.7 g/kg for stems. Added P fertilizer increased P concentration in the three tissues, but the effect was most pronounced for blades of plants without added Zn. Magnesium concentration at maturity was mainly affected by N fertilizer.and ranged from 1.6 to 1.9 g/kg for seed, 4.0 and 9.7 g/kg for blades, and 4.0 to 7.1 g/kg for stems. Soil management can greatly affect Zn concentration in navy bean seed.     

Nitrogen balance of nitrogen-15 applied as ammonium sulphate to irrigated potatoes in sandy textured soils

Farmers are applying very high amounts of N fertilizer (sometimes >900 kg N/ha), commonly (NH₄)₂SO₄, to irrigated potato (Solanum tuberosum, L.) grown on sandy textured soils in the Cappadocia region of Turkey. To obtain information on potato yield, N uptake, N fertilizer residue in the soil and the portion of N fertilizer leached below 200 cm soil depth, nine field experiments were conducted at three different locations in 1992, 1993 and 1994. The N rates used in these experiments were 0, 200, 400, 600, 800 and 1,000 kg N/ha within a completely randomized block design with three replicates. N fertilizer was applied in two equal portions; one at planting and one just before the first irrigation. Although all yield data were used to find out the marketable tuber yield, the N rate response curve and the fate of applied fertilizer N was determined only for the 400 and 1,000 kg N/ha rates. Isotope microplots were established where ¹⁵N-labelled (NH₄)₂SO₄ was applied at 5.0 atom % and 2.5 atom % excess enrichments for the 400 kg N/ha and 1,000 kg N/ha rates, respectively. At harvest, marketable and dry tuber yield was determined for all N rates. Dry tuber and leaf plus vine yields were determined for the isotope microplots and they were analysed for the % N and ¹⁵N atom % excess. The % N derived from fertilizer and N use efficiency (%NUE) were calculated for the plant samples. The ¹⁵N-labelled residue left in 0-200 cm soil was also determined. The amount of N fertilizer leached below 200 cm soil depth was also calculated. ¹⁵N-labelled NO₃^- and total NO₃^- of the groundwater from wells were determined at different dates. Our results show that the optimum marketable tuber yield was obtained with 600 kg N/ha. Tuber N uptake was increased slightly, while leaf plus vine N uptake increased considerably when the N rate was increased from 400 to 1,000 kg N/ha. The %NUE values decreased nearly by half and the amount of N fertilizer in the 0-200 cm soil layer increased more than 3 times when the N rate was increased from 400 to 1,000 kg N/ha. Nearly half of the applied fertilizer N (45.6%) at 400 kg N/ha and more than half of the applied fertilizer N (60.8%) at 1,000 kg N/ha was still in the 0-200 cm soil layer after harvest. Four times more N fertilizer was leached below 200 cm soil depth when 1,000 kg N/ha N was applied instead of 400 kg N/ha. Our results also indicate that there is a potential contamination of groundwater due to leaching of the applied N fertilizer.     

Sulphur and nitrogen nutrition and misting effects on the response of bluegrass to ozone,sulphur dioxide,nitrogen dioxide or their mixture

Kentucky bluegrass (Poa pratensis L.) plants, cultivars Cheri, Merion and Touchdown were grown at complete nutrition or with low S or low N. Plants were exposed to 10 ppm (v/v) O₃ for 6 h d^?i, 15 pphm SO₂ continuously, 15 pphm NO₂ continuously, or their mixture at these concentrations for 10 days. The severity of injury was much increased by misting with deionized water for 5 min twice daily, especially with SO₂ and NO₂ single gas exposures. The misting did not have consistent effects on total S, total N, leaf area or fresh weight. Exposure to O₃ decreased leaf area without affecting S or N content, while SO₂ usually increased total S and, in some cases, increased total N. Exposure to NO₂ increased total N without affecting total S, and the mixture increased both total S and total N. Low S or low N usually enhanced the effect of SO₂ or NO₂, respectively. Leaf area and fresh weight were not as responsive to the treatments as total S and total N. Rainfall outdoors may be a major meteorological factor affecting plant injury response to gaseous pollutants.     

接触施用包膜控释肥对玉米产量、根系分布和土壤残留无机氮的影响

采用田间小区试验,研究了习惯施肥与接触施用包膜控释肥料对夏玉米生长、产量、根系分布和土壤无机氮残留的影响。结果表明,接触施用包膜控释肥料没有抑制玉米的出苗和幼苗生长;减氮1/3的控释肥处理(N 120kg/hm2)与习惯施肥处理(N180 kg/hm2)的玉米产量没有差异。在0—30 cm土层,与对照和习惯施肥处理相比,接触施用控释肥增加了距茎基部0—10 cm区域内玉米根长密度的分布,占总根长的59%~64%;玉米收获后,减量控释肥处理土壤剖面各个土层Nmin含量与对照相比无显著增加,习惯施肥和全量控释肥处理(N 180 kg/hm2)在60—90、90—120 cm土层的Nmin累积显著高于对照。综合考虑玉米生长、产量以及根系分布和氮素淋失风险,本试验条件下,接触施用控释肥N120 kg/hm2是夏玉米季较为理想的选择。     

Sulfur status of volcanic ash‐derived soils in Hawaii

Abstract

Several rainwater samples and 14 profiles of Hawaii's volcanic ash‐derived soils were analyzed for sulfur (S). Atmospheric deposition was an important S source at the coast (24 kg S/ha), but its contribution decreased with increasing distance from the sea (1 kg S/ha at 24‐km inland). The S concentration of rainwaters also decreased linearly with increasing rainfall.

Several thousand mg SO₄‐S/kg can be extracted from many volcanic ash‐derived soils of Hawaii, and it was often required at least four extractions [0.04 M Ca(H₂PO₄)₂, 1:10 soil to solution ratio] to completely desorb this SO₄. There was a close association of high SO₄ retention with high rainfall. This might have resulted from (1) the development of a solid phase with high SO₄ retention under intense weathering conditions, (2) more total SO₄ received by the soils from atmospheric deposition, and (3) past fertilization of sugarcane grown in high rainfall areas.

Low concentrations of soil solution SO₄‐S in relation to large amounts of P‐extractable SO₄ suggest that a S bearing mineral, such as basaluminite, may be controlling soil‐solution SO₄. Furthermore, SO₄ adsorption isotherms of these volcanic soils generally show a bi‐phasic property, and suggest that 40 to 80 mg SO₄‐S/kg is required to maintain 3 ‐ 6 mg SO₄‐S/L in the soil solution, a concentration range considered adequate for the growth of most crops.     

The effect of nitrogen and boron soil applications on raspberry leaf N,B and Mn concentrations and on selected soil analyses

Abstract

Four years after yearly applications of N (0, 67, 134 and 268 kg/ha in a N rate trial) soil pH and soil extractable K, Ca and Mg were reduced. Boron application (1 kg/ha in a N x B interaction trial) increased hot water extractable soil B and soil extractable Mg. Old and new cane leaf N concentration was increased by N application but B application resulted in only a very small effect. Both N and B applications increased leaf B concentrations. Leaf Mn was increased by N application, probably because of the reduced soil pH. Boron had little effect on leaf Mn. It was concluded that leaf tissue is not suitable for determining the requirements of N and B fertilizer because of the instability of B concentrations in the leaves within and between seasons. Sampling of new cane leaves in July showed promise for diagnosing Mn requirements since the concentration during that month was relatively stable in three separate years of sampling.     

Nitrapyrin effect on corn N‐15 uptake efficiency,denitrification and nitrate leaching

Abstract

The effect of nitrapyrin on the fate of fertilizer nitrogen (N) applied to soil needs further investigation. Our objective was to determine the effect of nitrapyrin under two different leaching regimes on the fate of ammonium sulfate‐nitrogen [(NH₄)₂SO₄‐N] added to the soil, namely corn N uptake, denitrification, nitrate leaching and soil residual N. A Nunn sandy clay loam soil (fine, montmorillonitic, mesic, aridic, argiustoll), low in residual inorganic N was used. Nitrogen‐15 enriched (NH₄)₂SO₄ (5 atom% N‐15) was applied at five rates (0, 50, 100, 200, and 400 mg/kg), nitrapyrin at three rates 0, 1.3, and 2.6 μL/kg (0, 2.36, and 4.72 L/ha) and leaching at two rates (0 and 1000 mL over field capacity in two 500‐mL increments at 3 and 6 weeks after planting) in a complete factorial arrangement with three replications. Corn (Zea mays L.) seeds were planted in pots (2 kg soil/pot) and allowed to grow for 80 days in a greenhouse. The atom% N‐15 values were determined in plant tops, leachates and soil samples using a mass spectrometer. The results showed that N fertilizer increased dry matter production, plant N concentration, leaching of nitrates and denitrification significantly. The effect of nitrapyrin on yield was not statistically significant, but, it at a rate equivalent to 4.72 L/ha reduced denitrification and nitrate (NO₃) leaching and increased N uptake efficiency. Application of 4.72 L/ha of nitrapyrin versus control showed the following results respectively, N uptake: 46.3 versus 39.6%, denitrification: 26.3 versus 35.3% and NO₃ leaching: 2.7 vesus 6.7% of fertilizer N‐15. Nitrapyrin increased soil residual fertilizer N‐15 in organic matter and roots. The result of this study show that application of nitrapyrin at an adequate rate decreases denitrification and NO₃ leaching and increases N uptake efficiency.     

The effect of time of S application on yield and sulphur uptake of canola

Abstract

Little information was available on the yield response of canola species to application of sulphur (S) fertilizer at various times after seeding. Split plot experiments having two cultivars, ‘Candle’ (Brassica campestris L.) and ‘Regent’ (Brassica napus L.) as main plots and four times of applying S fertilizer as subplots after seeding (0, 14, 28 and 42 days) were set out on six sulphur deficient soil sites of northern Saskatchewan. Sodium sulphate fertilizer was applied at 25 kg S/ha and all plots received 100, 20 and 50 kg/ha of N, P and K, respectively. The cultivar ‘Regent’ yielded 1.24 t/ha which was significantly higher than ‘Candle’ yielding 0.98 t/ha (average over sites). An estimated linear reduction in yield of canola grain of 0.11 t/ha for ‘Candle’ and 0.40 t/ha for ‘Regent’ was obtained with S applied at 42 days after seeding date. This difference in response to time of S application resulted in a cultivar x time of S interaction. On two other sites testing high in S (above 40 kg S/ha) there was an apparent increase in grain yield with S application at the rosette stage and at the second application time (12 days before reseeding because of frost damage). Sulphur uptake in grain and straw was highly correlated with yield of grain and straw. Average uptake of S in straw (15.1 kg S/ha) was higher than in grain (4.4 kg S/ha). With few exceptions, yield and S uptake in grain and straw was less with S fertilizer applied at late stages of growth than at seeding.     

Effect of sulfur rate,application method,and source on yield and mineral content of corn

Abstract

Corn (Zea mays L.) grown on sandy Coastal Plain soils may be subject to sulfur (S) deficiency due to the low levels of available S in the soil. The diagnosis of S deficiency in the field is sometimes ambiguous since mineralization of soil organic matter or root growth into the subsoil may supply adequate S to the crop. Yield response to S fertilizers has been more frequent since incidental additions of S to the soil by air pollution and fertilizer applications have been reduced. This study was conducted to identify S deficiency in corn grown on sandy Coastal Plain soils and to determine the effects of S source, rate and method of application on grain yield. Irrigated corn was grown on Norfolk loamy sand and Tifton loamy sand near Leesburg and Moultrie, Georgia, respectively in 1987. Grain yields were increased with addition of 11 kg S ha^‐1 compared to the check treatment. Increased rates of S up to 88 kg ha^‐1 did not increase grain yields above the 11 kg ha^‐1 rate. There was no difference between banded or broadcast application of (NH₄)₂SO₄ or between elemental S and (NH₄)₂SO₄ as S sources. Earleaf S concentrations of 1.6 g kg^‐1 and extractable soil S concentrations of 4.0 to 8.7 mg kg^‐1 were associated with S deficiency. Visual symtoms of S deficiency were observed in the check treatments throughout the growing season at both experimental sites. The results indicate that visual symptoms and tissue analysis can be used to identify S deficiency. Extractable soil S may be useful in determining the possible response to S fertilizer especially if the subsoil is sampled.     

Interaction of salinity,nitrogen, and phosphorus fertilization on wheat

This study determined whether the application of nitrogen (N) and phosphorus (P) could ameliorate salt‐induced reduction in wheat production. Saline irrigation water (0.5, 4.0, 8.2, and 12.5 dS/m) and N and P fertilizers (150 kg N/ha and 37.5 kg P₂O₅/ha) were applied to wheat (Triticum aestivum L. ‘Saka 92') grown on a calcareous soil in a greenhouse experiment. Plants received equal amounts of each fertilizer, but the time and frequency of application differed. All salinity levels reduced straw and grain yields, leaf soluble proteins, nitrate (NO₃) content, actual and potential nitrate reductase activity (NRA), and grain protein content. The delay in pollen meiotic cell division increased with salinity. Under saline conditions, applying N and P fertilizers at the end of the grain filling stage improved yield and metabolic performance of the plants compared to other fertilizer treatments.     

Effect of nitrogen fertilization on yield and nitrogen and water use efficiencies of winter wheat (durum and bread) varieties grown under conditions found in Central Anatolia

In order to evaluate the influence of different N rates on percent N derived from fertilizer (%Ndff) at different growth stages, on yields and the percent N use efficiency (%NUE) values of two winter wheat varieties (durum and bread), field experiments on fallow were carried out at four different locations in Central Anatolia, in the 1991–1992 and 1992–1993 growing seasons. At each site the rates of N (0, 40, 80 and 120?kg N/ha) were applied as ammonium sulphate [(NH₄)₂SO₄] using a Latin Square experimental design with four replicates. The total amounts of N fertilizer were applied once after seedling emergence at all experimental sites. Labelled (¹⁵NH₄)₂SO₄ fertilizer was applied to sub-plots from which %Ndff values were determined at tillering, booting, grain filling, and harvest stages. Yield sub-plots received unlabelled (NH₄)₂SO₄ from which total dry matter (seed and straw) and N yields were determined. Also the %NUE values were calculated by the ¹⁵N and "difference" methods at the harvest stage. Stored soil moisture at 0–90?cm depth, evapotranspiration and water use efficiency values were calculated as well. The results obtained showed that (1) Gerek-79 variety used both the applied N fertilizer and the available soil moisture more efficiently, (2) the percent NUE values obtained overall were generally less than 20 for both varieties and (3) with the ¹⁵N method, less variable %NUE values were obtained in comparison to the difference method.     

Evaluation of Selected Extractants for Plant-Available Silicon in Rice Soils of Southern India

The extractable silicon (Si) using selected extractants irrespective of the soils used for the study was in the order of 0.005 M sulfuric acid (H₂SO₄) > 0.1 M citric acid > N sodium acetate (NaOAc) 2 > N NaOAc 1 > 0.5 M acetic acid 3 > 0.5 M acetic acid 2 > 0.5 M acetic acid 1> 0.01 M calcium chloride (CaCl₂) > 0.5 M ammonium acetate (NH4OAc) > distilled water 4 > distilled water 1. Silicon extraction with N NaOAc 1 appeared to be the most suitable for evaluating Si, followed by extraction with 0.5 M acetic acid 2 and N NaOAc 2. These extractants showed the greatest degree of significant correlation with the percentage of Si in straw and grain, as well as Si uptake by straw and grain. These methods also rapidly extract soil Si in comparison to the other methods and appear to be the most suitable for routine soil testing for plant-available Si in the rice soils of southern India.     

松嫩平原黑土区玉米生产氮磷配合肥效优化模型的研究

通过对黑土区玉米生产氮磷肥配合多年多眯次的试验研究,建立产量与肥效地优化模型,优化解析出黑土区玉米生产氮磷含最佳用量的Ｎ１７２．９ｋｇ／ｈａ,Ｐ２Ｏ５５７．４ｋｇ／ｈａ,氮磷比为３．０：１,可获得最佳产量７７９１．０ｋｇ／ｈａ;最佳用量范围内,氮,磷用量相同时,平均每公斤氮可增产玉米１４．４ｋｇ,每公斤磷可增产玉米１６．９ｋｇ,磷的肥效比氮好,但氮的增产潜力远比磷大,单施磷可增产玉米７３４．９ｋｇ     

Nitrogen balance studies in the central plain of Thailand

At Chainat, in the central plain of Thailand, where problems of double cropping are being investigated, a growth rate and nitrogen uptake rate for maize of 370 and 3.15 kg/ha/ day respectively were obtained. In one season there was a high positive correlation between maximum nitrogen yield and maize grain yield.When ¹⁵N-labelled (NH₄)₂SO₄ nitrogen was applied to maize at 100 kg/ha of N, 49 per cent could be recovered in tops after 12 weeks. After 8 weeks, 23 per cent was in the soil organic N plus roots, and after 12 weeks had decreased to 10 per cent. In the same period, the unaccountedfor fertilizer N had increased from 27 per cent at 8 weeks to 41 per cent at 12 weeks.In a long term rotation experiment involving 18 dry and wet season cropping combinations, a provisional balance sheet after two years indicates (1) that the soil nitrogen status can be maintained with the introduction of high input, dry season upland crops into a cropping system where wet season rice is grown only, (2) that in the absence of nitrogen fertilizer about 40 kg/ha of N is added per season to the soil-plant system under rice, and (3) that mung bean (Phaseolus aureus) fixes between 58 and 107 kg/ha of N per season.