摘要:

Dispersed, simple fertilizer trials on irrigated wheat crop were laid out in farmers' fields spread over 280 locations in Afghanistan extending over three seasons during 1970 to 1973. The 219 locations from which data could be collected were partitioned statistically into three arbitrary soil fertility classes by juxtaposing the “compound Baule” computed from soil test data with the corresponding check plot yield in each location. Adopting a graphical procedure, we fitted a three-nutrient Mitscherlich-Baule generalized yield equation to the grain yield data; we also worked out the economic optima in respect of “maximum profit” and “maximum return” considerations and the corresponding fertilizer rates for each group of soils. We found that the potential maximum yield of grain wheat on all types of soils in the country was estimated as 6232 ± 827 kg per ha, and that the greatest economic advantage would accrue if most of the available fertilizers could be applied to the less fertile soils. Regression equations have been presented for estimating the β parameter of the generalized yield equation from soil test values, in order that fertilizer rate recommendations could be formulated for other, similar areas in the country and for the situations when the cost/price ratio changes or management norms improve.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

After more than half a century of research on the effect of soil pH and aluminum toxicity on corn (Zea maysL.) growth, there still is no general agreement on whether soil pH or some measure of potential aluminum toxicity, such as aluminum saturation, should be the criterion used to estimate the likelihood of lowered yields in acid soils. Corn was grown for two years in two acid (pH 4.7) Ultisols (Wharton soil, and Murrill soil) in Pennsylvania with lime rates up to 16 metric tons per hectare. Grain yield was significantly reduced (p< 0.05) when the pH was less than 5.5 in the Wharton soil, whereas it was not significantly reduced in the Murrill soil until the soil pH was less than 4.9. In both soils the relative grain yield was lowered to 90 percent of maximum when the aluminum saturation exceeded 12 percent. These results indicate that aluminum saturation was a more accurate indicator than soil pH for predicting corn yield reductions in these acid soils. It is suggested that the low aluminum saturation in the Murrill soil at soil pH values of less than 5.0 was due to the very high available phosphorus level in this soil.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Soil salinities measured by salinity sensor (ECs), pressure vacuum cup (ECp), and bulk soil conductivity (ECa) were compared with that obtained by the saturation extract method (ECe) in a field experiment. There was a significant correlation betweenECa,ECs, andECp, each withECe. The soil resistivity method appears to be quite appropriate for surveying large tracts of salt-affected soils using these regression equations.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

A cooperative study was conducted with Pennsylvania State University to assess the effects of wastewater irrigation on the status of soil phosphorus. The major objectives of the research were to evaluate the influence of wastewater irrigation on changes in soil organic carbon, nitrogen, and phosphorus and the sorption of orthophosphate (P). Soil samples were obtained in 1974 and 1975 from Hublersburg silty clay loam cropped to corn (Zea maysL.), Reed canarygrass (Phalaris arundinaceaeL.), or a mixed forest and from a Morrison sandy loam with a mixed forest stand. The sites had been irrigated with secondary effluent for 11 to 12 years. Soil analyses indicated that the majority of phosphorus added to soils during wastewater irrigation remained in the upper 30 cm of the Hublersburg clay loam soil. In contrast, appreciable amounts of P had leached to the 30 to 60-cm depth in the Morrison sandy loam. The equilibrium phosphate concentration (EPC) increased markedly at the 0 to 15-cm depth as a result of wastewater irrigation, due to sorption of P added in the wastewater. As expected, the maximum P sorption capacity of soils was decreased by wastewater irrigation. A comparison of soluble P levels in leachate samples collected in the field at a 120-cm depth with soluble P predicted by EPC measurements indicated that laboratory measurements overestimate the ability of a soil to remove P from wastewater. Thus, wastewater may not interact with all potentially available P sorption sites in soils. The EPC and P sorption capacity of soils irrigated with wastewater was reduced by extracting soils with oxalate and citrate-dithionite-bicarbonate. These results indicated the significance of hydrous iron oxides in P retention by soils irrigated with wastewater.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Four methods of observing and measuring root proliferation of sorghum plants were compared. Plants were grown under artificial lighting in portable lysimeters of 160-liter capacity. The two nondestructive methods were (1) measuring roots visible through glass in place throughout the 77 to 80-day growth period, and (2) measuring roots through ports covered with polyethylene film, which was pressed against the soil by 3.5 kPa2of air pressure. This method is new. Destructive methods were (3) measuring length, and (4) weighing roots recovered from soil samples. The polyethylene-covered ports gave good visibility and adjusted to the moderate shrink-swell movements of the sandy loam soil. In contrast, gaps developed between glass and soil in the upper half of the 108-cm-deep lysimeters. Lack of contact between glass and soil and proliferation of roots intercepted by the glass hindered accurate observation. Root-growth rates, measured through polyethylene-covered ports, correlated significantly with those from soil-recovered roots, but growth rates measured through glass panels did not. Because far fewer roots were measured by nondestructive techniques, they had greater data variance than measurements of soil-recovered roots.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Respiration and nitrogen immobilization of the fresh organic layer of an acid podzol were studied, after pretreatment with sulfur, to simulate sulfur treatment of microsites when sulfur-coated urea is applied to the soil. The laboratory incubations were done at 10 and 20°C with several levels of urea application. Urea hydrolysis was slowed down considerably at 10°C in materials that had been pretreated with sulfur. Sulfur pretreatment modified the increase in pH and respiration caused by urea application but had little influence on the availability of ammonium nitrogen. The lower temperature allowed adequate fertilizer nitrogen recovery from moderate dosage rates that produced a pH lower than neutrality. At the higher temperature, fertilizer nitrogen recoveries were very poor. At higher pH, a large part of the immobilization of nitrogen appears to be nonmicrobial.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

Efficient disposal of waste oil sludges by biodegradation in soil (“land farming”) requires management practices that include fertilizer addition. The effect of such practices on soil leachate quality was studied in lysimeter columns containing 5 percent (wt/wt) hydrocarbon in a soil-sand mixture. Fertilizer was added in various formulations at a carbon:nitrogen and carbon:phosphorus ratio of 200:1 and 2640:1, respectively. As expected, undegraded hydrocarbons did not appear in the leachate, nor was phosphate eluted from the limed soil-sand mixture. A very moderate increase in total organic carbon of the leachate occurred due to hydrocarbon biodegradation. When nitrogen was applied as urea or as a urea-paraffin adduct, 23 and 19 percent of the added nitrogen were eluted in the leachate, respectively. No nitrogen appeared in the leachate when nitrogen was applied as urea formaldehyde. The above results and additional cited reports indicate that judiciously located and operated land-farming sites are not likely to endanger underground aquifers.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

The dissolution in two acid soils (Weston, pH 4.5; Davidson, pH 5.2) of phosphorus from North Carolina phosphate rock, a highly reactive rock, was decreased by additions of (NH4)2SO4or their mixtures, but increased by the addition of urea. The effect of urea was decreased by addition of KCI. It is concluded that urea hydrolyzes the organic matter of the soil and that the products of hydrolysis chelate calcium ions and so increase the dissolution of phosphorus from the rock. (NH4)2SO4and KCI, on the other hand, increase the phosphorus-sorption capacity of the soil and so decrease the water-soluble phosphorus in the soil. The results suggest that the beneficial effects of nitrogen and potassium fertilizer salts on the uptake of phosphorus by plants may result from stimulation of plant growth and not from solubilization of phosphate rock.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

摘要:

The effects of three grasses and five leguminous covers, grown on an eroded tropical Alfisol for two years, on soil properties were investigated. Improvements in soil characteristics underBrachiaria, Paspalum, Cynodon spp., Pueraria, Stylosanthes, Stizolobium, Psophocarpus,andCentrosemawere compared with that of weed-fallow control. There were significant improvements in soil organic matter, total nitrogen, cation exchange capacity (CEC), infiltration rate, moisture retention at low suctions, and soil bulk density under various grass and leguminous fallow compared with control.

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID

ISSN:0038-075X    

出版商:OVID    

年代:1979

数据来源: OVID