摘要:

Considerable within‐field variation in the N content and appearance of sugarbeet (Beta vulgarisL.) leaf canopies is found often at root harvest. Since this heterogeneity can affect subsequent soil N mineralization, a study was initiated to determine if the within‐field variation could be identified and located by aerial photography and a global positioning system (GPS). An aerial color photograph was taken of a commercial sugarbeet field prior to harvest. Three reflectance patterns associated with different degrees of canopy greenness ("green”; [G], “yellow‐green”; [YG] and “yellow”; [Y]) were identified readily. Four areas, each approximately 0.8 ha in size, with these three canopy types were selected. The canopy subsites were located by use of a GPS unit. The G, YG, and Y canopy types contained 277, 138, and 85 kg N ha‐1, respectively, in sugarbeet tops. The corresponding leaf N concentrations were 30.6, 20.1, and 15.8 g kg‐1, respectively. Postharvest soil NO3‐N levels in the upper 120 cm of soil were 57, 14, and 10 kg ha‐1for the G, YG, and Y canopy sites, respectively. Nitrate‐N in sugarbeet tops returned to the soils was at least partly responsible for the higher soil NO3‐N at the G subsites. In contrast to dry matter yield, recoverable sugar yield was significantly less for roots associated with the G‐canopy type than for roots associated with the YG‐and Y‐canopy sites. Aerial photography and GPS technology can increase precision of soil testing for NO3‐N after a sugarbeet crop, help to identify areas of increased soil N mineralization for a subsequent crop, and decrease subsequent N fertilizer use if a variable rate N‐fertilizer applicator is used.

ISSN:0010-3624    

DOI:10.1080/00103629809370168

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The fate of crop residue and animal manure applied to soil is important for agriculture in the mixed farming systems of semi‐arid tropics. Organic matter (OM), nitrogen (N), and phosphorus (P) losses from a variety of crop residues and browse leaves were compared to the manures of sheep fed the same plant materials in the semi‐arid region of Niger in West Africa. All organic residues decomposition and mineralization were measured using litterbag techniques in a Labucheri soil (sandy siliceous, isohyperthermic Psammentic Paleustalf) during the dry, wet, and cool seasons. Losses of OM, N, and P were generally greater and more rapid during the wet than the dry and cool seasons. Greater initial losses of OM, N, and P occurred in manures than in most browse leaves, particularly during the dry and the cool seasons. Differences in the rate and magnitude of OM losses were related to seasonal effects. For manures, sheep diet affected net mineralization profoundly in the initial stages of decomposition, but differences were reduced over longer periods of times. The total amount of N released from manures generally increased in the order of Pennisetum < Ficus ≤ Pterocarpus ≤ Anogeisus ≤ Combretum ≤ Vigna ≤ Mitragyna ≤ Guiera ≤ Acacia diets. For crop residues, more N and P were mineralized from Vigna than Pennisetum leaves whereas net N and P immobilization occurred for browse leaves, especially during the dry and cool seasons. The passage of feed through ruminants is clearly an important regulator of nutrient cycles in this semi‐arid region. Predicting seasonal OM decomposition and nutrient release rates may provide crop residues and livestock management strategies to improve crop growth.

ISSN:0010-3624    

DOI:10.1080/00103629809370169

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

All techniques used to measure soil water content have errors associated with them. These errors are further propagated when soil volumetric water contents are numerically integrated over a number of depth intervals to estimate the soil water storage for the entire profile. Previous studies had field‐tested the performance of a commercial capacitance probe (Troxler Sentry 200‐AP). The probe was calibrated and the measured data on crop water use were compared with that reported previously in literature using other instruments. However, the errors associated with the field estimates of soil water storage and crop water use measured with the Sentry 200‐AP capacitance probe were not evaluated. The objective of this study was to analyze these associated errors. Equations were derived to evaluate the errors incurred in calculating the volumetric water content using the fitted field calibration curve for the Sentry 200‐AP capacitance probe and in the estimates of the crop water use. This study suggests that the error in making in situ measurements of soil water content in heterogeneous soil systems using the Sentry 200‐AP capacitance probe depends on the degree of saturation at the point of measurement in the soil profile. The Sentry 200‐AP capacitance probe produces errors of >5% in measuring soil volumetric water contents of >35% in heterogeneous soil systems.

ISSN:0010-3624    

DOI:10.1080/00103629809370170

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Applications of zinc (Zn) and copper (Cu) at excessive rates may result in phytotoxicity. Experiments were conducted with mixtures of soils that were similar except for their Zn and Cu levels. The critical toxicity levels (CTL) in the soils and plants for these elements were determined. Peanut (Arachis hypogaeaL.), soybean [Glycine max(L.) Merr.], corn (Zea maysL.), and rice (Oryza sativaL.) were the crops grown. One soil mixture had Mehlich 3‐extractable Zn concentrations up to 300 mg dm‐3with no corresponding increase in soil Cu; two soil mixtures had soil Zn concentrations up to 400 and 800 mg dm‐3with a corresponding increase in soil Cu up to 20 and 25 mg dm‐3, respectively; and four soil mixtures had no increase in soil Zn, but had Mehlich 1‐extractable Cu concentrations from 6 to 286 mg kg‐1. Under a given set of greenhouse conditions, the estimated Mehlich 3‐extractable Zn CTL was 36 mg dm‐3for peanut, 70 mg dm‐3for soybean, between 160 and 320 mg dm‐3for rice, and >300 mg dm‐3for corn. No soil Cu CTL was apparent for peanut or soybean, but for corn it was 17 mg dm‐3and for rice 13 mg dm‐3. With different greenhouse procedures and the Mehlich 1 extractant, the soil CTL for rice was only 4.4 mg kg‐1. Therefore, peanut and soybean were more sensitive to Zn toxicity, whereas corn and rice were more sensitive to Cu toxicity. Plant Zn CTL for peanut was 230 mg kg‐1, while that for soybean was 140 mg kg‐1. Copper appeared to be toxic to corn and rice at plant concentrations exceeding 20 mg kg‐1.

ISSN:0010-3624    

DOI:10.1080/00103629809370171

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Continued introduction of new boron (B) fertilizer materials prompted a second examination of the efficacy of foliar‐applied B materials on B content, B uptake, and dry matter yield of cotton (Gossypium hirsutumL.) and soybean (Glycine maxL.). Similar to a previous study, this greenhouse study was conducted at four participating universities using 6‐week‐old cotton (Deltapineland 90) and soybean (Pioneer 9761) plants. Sources and rates of B were 1) boric acid (17.5% B) at 0.22 kg ha‐1,2) sodium borate (Solubor® 20.5% B) at 0.22 kg ha‐1, 3) Smith & Ardussi Liquid B (10% B) at 0.22 kg ha‐1,4) Smith & Ardussi Liquid B at 0.11 kg ha‐1, 5) Borosol 10 (10% B) at 0.22 kg ha‐1, 6) Borosol 10 at 0.11 kg ha‐1, and 7) an untreated control. Control plants that did not receive B were sprayed with water. Four plants were grown in each 15‐cm diam. pot in sandy loam soil. Plants were sprayed at 6 weeks of growth and top growth was harvested at eight weeks. Whole‐plant samples were dried (70°C), ground, and analyzed for B content. Uptake of B, plant B concentration, and plant dry weight varied by state, so results were not combined over all states. In every state there were significant differences in B concentration and B uptake by cotton and soybean as affected by B treatment, but effects were not consistent with any one B source. In two of four cases (Alabama and Georgia) cotton plants receiving any B treatment had greater B concentration and B uptake than the water‐sprayed control. In Virginia and North Carolina, application of B treatments rarely affected B uptake by cotton or soybean. No one B source produced consistently greater B uptake than any other B source.

ISSN:0010-3624    

DOI:10.1080/00103629809370172

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A nutrient solution experiment was performed to assess the importance of fluctuations in substrate cadmium (Cd) concentrations during plant growth on Cd uptake by cucumber plants (Cucumis sativusL.). Nutrient solution Cd was varied between 0 and 5 μg L‐1in a way that the average Cd concentration over the entire growth period was 2.5 μg L‐1for all treatments. Slight but significant (p=0.05) differences in shoot dry matter yield reflected a negative effect of Cd on growth. Alternating Cd in solution every two days between 1.5 and 3.5 mg L‐1or between 0 and 5 μg L‐1had no different effect than supplying a constant Cd level of 2.5 μg L‐1during growth and indicated a linear response of the plant to substrate Cd concentration. Experimental treatments where Cd in solution either decreased or increased during the growing period resulted in a lower and a higher plant Cd concentration, respectively, compared to the treatment involving a constant solution Cd concentration of 2.5 μg L‐1. Short time random fluctuations in solution Cd concentration will not influence the final Cd concentrations in crops. Prediction of Cd uptake from soil extraction data will be most reliable when based on a good estimate of the average soil solution concentration towards the end of the plant growing period.

ISSN:0010-3624    

DOI:10.1080/00103629809370173

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0010-3624    

DOI:10.1080/00103629809370174

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The effect of alternating waterlogged and drying conditions on phosphorus (P) availability and sorption was studied in three soils of contrasting chemical and physical properties. Soils were treated with two levels of P (0 and 50 mg kg‐1; P0 and P50), waterlogged for 21 days, then allowed to dry at room temperature for 14 days. The availability of P, iron (Fe), and manganese (Mn) over the waterlogged and drying periods was determined by shaking samples of each soil with 1M NaOAc (pH 3). Increasing concentrations of 1M NaOAc (pH 3) extractable P (Pac) over the waterlogged period was attributed to solubilization of Fe(OH)3materials under reducing conditions with the release of sorbed and occluded P. The released P appeared to be resorbed by freshly precipitated amorphous Fe(OH)2material since earlier studies showed that water soluble P concentrations in these soils were reduced to negligible levels under waterlogged conditions. The Fe(OH)2material remained readily extractable with 1M NaOAc (pH 3) since Feacincreased dramatically with waterlogging. Drying the waterlogged soils caused a rapid decrease in Pac,Feacand Mnacsuggesting the Fe(OH)2may have been transformed into more stable forms [e.g., Fe(OH)3]. Much of the changes in Pacappeared to be due to changes in Feac, with limited influence from Mnac. and mineralization of organic P. Phosphate sorption isotherms were determined using the standard batch technique for air‐dry, waterlogged (with and without ponded water), and waterlogged/dried conditions. Sorption isotherms were not affected by waterlogging and subsequent drying. Most soils sorbed all of the added phosphate irrespective of moisture treatment.

ISSN:0010-3624    

DOI:10.1080/00103629809370175

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A labeled goethite was synthesized, using oxygen‐stable isotope18O, in order to reveal ligand exchange reactions accompanying selenite sorption on the particles. The18O isotope ratio of the surface hydroxyl groups on the labeled goethite was estimated to be 3.2% or 4.8% (depending on the assumed cases) by measuring the increase in the18O isotope ratio of water molecules of the solutions through fluoride sorption on the goethite. The amount of oxygen atoms from surface hydroxyl groups on the labeled goethite released by selenite sorption was estimated, approximately, by the measurement of changes in the oxygen isotope ratio of water molecules in the reaction solutions. The δ18O value of the selenite sorptive solutions was apparently increased, suggesting that ligand exchange reactions occurred between selenite ions and the surface hydroxyl groups on the labeled goethite. The results suggested that the ligand exchange reactions of selenite sorption consisted of 6 to 40% of reaction in which oxygen atoms of the surface hydroxyl groups were released from the particles and of 60 to 94% of the alternative reaction in which oxygen atoms of selenite ions were released into the solutions, if the reaction sites for selenite sorption on the goethite are the samcas for fluoride sorption.

ISSN:0010-3624    

DOI:10.1080/00103629809370176

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The stem nitrate test for peppermint (Mentha piperitavar.) is a promising nitrogen (N) management tool. When used properly, this test may aid in obtaining significant savings of fertilizer costs and in the protection of groundwater quality. There are several factors related to environmental conditions, N management, and sampling procedures that have not been evaluated and may confound interpretation of test results. The objective of this study was to measure the response of stem nitrate concentrations to factors that would be expected to influence the test and develop guidelines for the collection of stem tissue. The factors considered here were i) solar radiation effects on both hourly and daily scales; ii) spatial variability; iii) differences between alternative plant materials; and iv) the temporal response of tissue nitrate concentrations to soluble N application. The most influential of these variables were the type of stem material (a 441% effect at p=3.55E‐6) and the number of stems collected to estimate the field mean concentration. It was found that the variance of the sample population and the number of stems required for a given sampling error could be greatly reduced by only collecting stems from within the plant canopy. Collecting only these stems, 30 stems were found to be adequate to estimate the field mean concentration within 10 to 15% of the true population mean (p<0.05). Statistically significant differences in stem nitrate concentrations were produced by variations in solar radiation on both hourly (p<0.05) and day length (p<0.01) scales. When measuring the diurnal response, a 17% reduction in stem nitrate concentration was observed over a nine‐hour period from 12:00 hours to 21:00 hours. On the day length scale, an 80% reduction in incoming solar radiation produced a 29% increase in stem nitrate concentrations after three days of shading. In the analysis of stem nitrate spatial variability, no discernable range of autocorrelation was detected indicating a purely random distribution of stem nitrate concentrations on the l‐150mscale. Given this finding and under the conditions of the analyses (late season with stem nitrate in excess of critical levels), it is not important that samples collected for this test fully cover the field being assessed, despite the intuitive appeal of full‐field sampling as a standard procedure. The response of stem nitrate concentrations to soluble N application was minimal, probably due to plant N status in the test plots being well above the critical deficiency content prior to application. With the data produced from these investigations, users of the peppermint stem nitrate test are presented with a method to collect data in the field whereby N management interpretations of the test can be more consistent and reliable. In addition, these results indicate the need for researchers to fully report the method of sampling employed when presenting finding for stem tissue tests.

ISSN:0010-3624    

DOI:10.1080/00103629809370177

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor