摘要:

Although it has been shown that the nitrogen (N) concentration of winter wheat(Triticum aestivumL. em Thell) at Feeke's growth stage 5 (GS 5) can be used to assist in making more accurate spring N fertilizer recommendations, the need remains to find a more convenient and accurate means for predicting N fertilizer needs of wheat. We conducted seven N fertilizer response experiments over two years in central and southeastern Pennsylvania to determine if chlorophyll meter readings of wheat leaves at GS 5 could predict whether a significant, positive grain yield response to N fertilizer would be obtained. The chlorophyll meter readings at GS 5 were more accurate (correctly predicting response to N fertilizer in 24 of 25 treatments for a 4% error rate) than GS 5 plant N concentration (20% error rate). There were too few treatments with a positive response to N fertilizer to be able to determine if chlorophyll meter readings could be used to accurately predict N fertilizer rates needed for economic optimum yield.

ISSN:0010-3624    

DOI:10.1080/00103629409369027

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A rapid test for measuring petiole sap nitrate‐N in potatoes was developed using a pH/ISE meter equipped with a nitrate‐ion specific electrode. Nitrate‐N measurements were made on fresh sap that was diluted with a solution of 0.075M Al2(SO4)3‐18H2O and 0.02M H3BO3. The sap nitrate‐N concentration, as determined by the rapid test, was highly correlated (r = 0.91, P<0.01) with dry matter nitrate‐N. Because of the non‐clogging design properties of the electrode used, this test procedure produced rapid and reliable results with good instrument stability and long electrode life. The chemicals used for this test are relatively non‐hazardous and the required tools can be assembled into a small portable kit. When properly calibrated, this test will provide added impetus to growers to rely on tissue analysis for corrective in‐season nitrogen (N) fertilization of potatoes.

ISSN:0010-3624    

DOI:10.1080/00103629409369028

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Evaluating the long‐term environmental effects of controlled‐availability nitrogen (N) fertilizers is best done with15N‐labeled materials. Simple bench‐scale methods not requiring elaborate apparatus are described for synthesizing15N‐enriched isobutylidene diurea (IBDU) and oxamide suitable for such purpose. IBDU is prepared by reacting15N‐labeled urea with isobutyr‐aldehyde. Oxamide is made by reacting15N‐labeled ammonia (NH3) with ethyl oxamate. No specific method but a general description is provided for synthesizing ureaform because the chemical composition of the family of polymers known as ureaform varies with reactant ratios and reaction conditions.

ISSN:0010-3624    

DOI:10.1080/00103629409369029

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An experiment was conducted in six locations in Nigeria to determine the optimum sampling depth and optimum number of core samples required for diagnosing soil nutrient status accurately for crop production. The optimum sample size varies significantly with soil type, sampling depth, and nutrient type. However, 25 to 30 and 30 to 40 core samples are recommended for newly opened land and intensively cultivated land, respectively. Samples taken within the 0–20 cm depth gave the highest significant relationship between soil test level and nutrient uptake.

ISSN:0010-3624    

DOI:10.1080/00103629409369030

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A method using isotopic dilution of carrier‐free sulfur (35S) for determining adsorbed sulfate (SO42‐) in soil samples from B horizons of podsolized soils was compared with an extraction of SO42‐ by 10 mM calcium dihydrogen phosphate [Ca(H2PO4)2]. The two methods gave comparable results for flesh soil samples while the extraction method resulted in significantly higher amounts of adsorbed SO42‐ when using air‐dried samples. Since the35S method assumes equilibrium between adsorbed SO42‐and SO42‐in solution, these results are evidence of complete exchangeability of adsorbed SO42‐extracted with Ca(H2PO4)2in fresh soil samples. It was thus concluded that the extraction method is a useful method when determining adsorbed SO42‐ in equilibrium with the soil solution in these soils. The35S reached equilibrium with the soil solution within 2 h. The difference between the methods when using air‐dried samples indicates that part of the adsorbed SO42‐ is irreversibly bound to the soil during air‐drying. Furthermore, it is recommended that the amount of SO42‐ determined in an extraction with water should be expressed as an intensity variable,i.e.,SO42‐ activity, rather than a capacity variable.

ISSN:0010-3624    

DOI:10.1080/00103629409369031

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An agronomic evaluation of phosphate rock (PR) on acid soils of Guarico and Anzoategui States was conducted to measure the effect on soil available phosphorus (P), grain yields of sorghum(Sorghum bicolor(L.) Moench) and soybean [Glycine max(L.) Merr.], and P absorption by these crops. Field experiments were established using a complete randomized block design with three replications. The treatments used were: triple superphosphate (TSP), North Carolina phosphate rock (NCRPR), compacted NCRPR with TSP at 60–40% and 70–30% (NCRPR 60/40 NCRPR 70/30), compacted Venezuelan Monte Fresco phosphate rock 60–40% and 70–30% (MFPR 60/40, MFPR 70/30), finely ground Monte Fresco phosphate rock (MFPR), finely ground Navay phosphate rock (NPR), and a check plot with no P source added. Five rates were applied, 0, 50,100,150, and 200 P2O5/ha, broadcasted and incorporated prior to planting. A basic fertilization of N, K, S, Mg, and Zn was uniformly applied to ensure an adequate supply of these nutrients. Soybean seeds were inoculated withBradyrhizobium japonicum.Soil samples were taken before planting and at harvest, and plant samples taken at critical growth stage (flowering) for tissue analysis, Crop grain yields were measured at 12% moisture content. The relative agronomic effectiveness (RAE) was calculted by the formula:RAE (%( = Yield of the rock − Yield of check plot/Yield of TSP − Yield of check plot × 100Maximum yields in all cases were obtained with TSP, however, in most cases there were no statistically significant differences between TSP and NCRPR as received or compacted (60/40 and 70/30). The compacted Venezuelan phosphate rocks also gave significantly higher yield and RAE responses showing the potential of these P sources for annual crops in the country. The finely ground Venezuelan phosphate rocks increased yields and RAE as compared to the check plot, but they gave the lowest response of all P sources. Soil available P after harvest had a tendency to increase where any source of P was applied or when the rates increased. The increment in soil available P was more evident when TSP and NCRPR as received and compacted were used. The lowest increments were reached with finely ground Navay phosphate rock. Leaf P concentration values were between the sufficiency range, except for those treatment where Monte Fresco and Navay finely ground phosphate rocks were applied at the rate of 50 kg P2O5/ha and for the check plot.

ISSN:0010-3624    

DOI:10.1080/00103629409369032

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The objective of this research was to determine the effects of tillage systems on selected chemical properties of a sloping and eroded soil which had previously been in sod. A tillage project was initiated in the spring, 1989 in southern Illinois on a soil with a root‐restricting fragipan. Corn (Zea maysL.) and soybean [Glycine max(L.) Mem] were grown on the plot area on a yearly rotation system. Prior to the application of lime or tillage treatments the 0–15 cm Ap horizon had a pH of 6.3, organic carbon (C) of 1.4 g/100g, and CEC equal to 17 meq/100g. Lime had been surface applied early in the spring of 1989 prior to moldboard (MP) and chisel (CP) plowing. Moldboard plowing had lower pH than the other treatments in the 0–5 cm layer in 1989 due to the moldboard plow mixing low pH subsoil material into the 0–5 cm layer and mixing surface applied lime into the 5–15 cm layer. During the 4th year, organic C was lowest for MP (1.28 g/100g) and highest for no tillage (NT) (1.65 g/100g), with CP having organic C content of 1.52 g/100g in the 0–5 cm layer. The differences in organic C were attributed to the effects of incorporation of plant residues below the 0–5 cm layer in the moldboard and chisel plow treatments. Effects of tillage on organic C content were not significant in the 5–15 cm layer. Soil phosphorus (P) (Bray Pl) and extractable potassium (K) were stratified, with the largest amounts of these two elements found within the top 5 cm of soil. In general, tillage did not have any significant (P=0.05) effect on either extractable calcium (Ca) or magnesium (Mg). Differences were observed in exchangeable ammonium‐nitrogen (NH4+‐N) and nitrate‐nitrogen (NO3‐‐N) by tillage treatments and were affected by soil moisture content and previous crop residues. Cation exchange capacity (CEC) was lower for MP at the 0–5 cm layer as compared to NT and CP in the 3rd year. At the 5–15 cm layer CEC was lower for NT as compared to CP and MP. The differences in CEC were attributed to the observed differences in organic C and possibly the effects of moldboard and chisel plow mixing subsoil materials slightly higher in clay content into the Ap horizon.

ISSN:0010-3624    

DOI:10.1080/00103629409369033

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Nitrogen (N) dynamics in the agriculturally important alluvial soils of the southern Mississippi Delta are not well understood, and little information is available regarding the amounts of various forms of N present in these soils. Profiles of nine alluvial soils were selected to represent the principal agricultural acreage in the southern Mississippi Delta. Soils were sampled by horizon to a depth of 150 cm and the distribution of various N fractions were characterized. Forty‐one additional chemical, physical and mineralogical properties were measured, and regression techniques were used to determine if these soil properties were related to N distribution in the highly heterogeneous soils typical of this region. These profiles contained 11.6 to 26.5 Mt N/ha (average 18.8 Mt N/ha). The surface 15 cm contained an average of 4.8 Mt N/ha and accounted for about 26% of the profile N. Most of N in the surface 15 cm was recovered as organic N (78.4–87.4%), and the balance recovered primarily as nonexchangeable ("clay‐fixed") NH4+. In subsurface horizons, nonexchangeable NH4+represented a substantially larger fraction of total N (average 35.6 %). The amounts of exchangeable NH4+and NO3‐ were very low in most samples and accounted for only 0.2–0.7% of surface N and 0.3–2.5% (average 0.7%) of the total N accumulated within horizons. The proportion of total N recovered as organic N was most closely related to organic carbon (C) content and the amounts of 2: 1 type of clay minerals present in the horizon. Even though subsurface horizons contained an appreciable portion of their N as inorganic nonexchangeable NH4+, organic C content was the best single indicator of total N content (r2= 0.931) within the 52 horizons studied.

ISSN:0010-3624    

DOI:10.1080/00103629409369034

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Lignin methods based on an acid‐detergent fibre pre‐extraction were evaluated for grass, straw, heather and spruce litter. Quantification following oxidative attack to destroy the lignin by permanganate proved to be unreliable for the woody heather material and spruce litter. In contrast the method of isolation involving hydrolysis of the cellulose component with 72% sulphuric acid (H2SO4) was precise and robust. The acid detergent reagent dissolves most of the hemi‐cellulose and offers the opportunity to quantify the residual alpha‐cellulose fraction.

ISSN:0010-3624    

DOI:10.1080/00103629409369035

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Coastal Plain soils in southern Maryland are typically acid (pH = 5.0±0.5) with low organic matter (1.2±0.5%), clay (2.8 to 9.8%), CEC (2.4 to 6.8 meq 100/g), and total Fe contents (4.5 to 34.9 g/kg). The objectives of this investigation were to assess the status of plant available molybdenum (Mo) in these soils by examining the extractable Mo levels in Ap horizon soil samples and tissue Mo contents in cured tobacco collected across a five‐county region. Seventy soil samples representing 11 soil series and 198 composite samples of tobacco served as the basis for the surveys. Plant available Mo in soil, estimated using a solution containing 0.18M ammonium oxalate and 0.1M oxalic acid as the extractant, ranged from 0.02 to 0.53 (ig/g and averaged 0.08 μg/g Mo. Three of the 11 soil series examined and 30% of the total soil samples exhibited extractable Mo levels ≤ 0.03 μg/g therefore may have less than adequate available Mo for tobacco. Cured leaf Mo contents ranged from non‐detectable to 7.95 μg/g and averaged 0.84±0.95 μg/g Mo. Approximately 15% of the leaf samples contained ≤ 0.2 μ/g Mo which approaches borderline deficiency for Mo with 12.2% having Mo contents within the range 0.2 to 0.4 ng/g where growth responses were reported in burley tobacco. The causes for the approximate one fourth of the plant samples having less than optimum Mo concentrations for maximum productivity for tobacco can likely be attributed to: 1) acid soils associated with inadequate liming programs; 2) very low extractable Mo levels in several soil series; and 3) excess input of SO4‐2in fertilizers and acid rainfall in the region which have been shown to inhibit MoO4‐2ion uptake by tobacco plants.

ISSN:0010-3624    

DOI:10.1080/00103629409369036

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor