摘要:

The soils of cassava‐growing areas of sub‐Saharan Africa were sampled in 1991 during the second phase of the Collaborative Study of Cassava in Africa (COSCA) in order to assess and document their fertility status. About 500 fields specifically grown to cassava or cassava‐based crop mixtures were sampled and the soils analyzed for nineteen physico‐chemical soil properties. The soil data reported in this paper were obtained from Cote d'Ivoire, Nigeria, Tanzania, and Uganda. The variations in soil properties as may be attributed to differences in climate, altitude, depth of sampling, and cassava intercropping systems were also analyzed. The soils used for cassava in these four countries were generally of medium to high fertility status. Herelow, medium, andhighfertility classes refer to soil nutrient levels where response by cassava to the application of such nutrients isdefinite, may be obtained, andnot expected, respectively. The fertility status across the agroecological zones ranges from high to low in the order: nonhumid>highland humid>subhumid>lowland humid. The soils used for cassava in the mid‐altitude zones were significantly more fertile than those of the low‐altitude zones. Similarly, soils from 0–20 cm depth contained significantly higher nutrients than those from 20–40 cm depth. Generally, soils grown to sole cassava or where cassava was considered a major or minor crop were statistically similar in terms of their nutrient contents. The nutrient ratings obtained from three scales suggest that the cassava‐growing soils are not ‘marginal’ in terms of both nutrient content and availability. Low levels of organic matter and total nitrogen (N) were the major soil constraints identified. Research needs to address these because the low nutrient reserve is essentially due to low organic matter levels in the soils.

ISSN:0010-3624    

DOI:10.1080/00103629809369934

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Laying hen litter [3.4% nitrogen (N), 0.86% phosphorus (P), 15% water (H2O)] as a fertilizer was evaluated in greenhouse production of strawberry(Fragaria ananassaDuch. cv. Oso Grande) and cos‐lettuce(Lactuca sativaL. cv. Amanthus). Litter was preplant soil incorporated at 7 (R1) and 14 (R2) ton ha‐1, and compared to ammonium nitrate (AN) (34–0–0) and an unfertilized (control) treatments. Rates of AN were at 150 kg N ha‐1for strawberry, in eight split applications, and 100 kg N ha‐1for lettuce, in two split applications. Preplant soil levels (mg kg‐1) of NO3‐N and P(H2O sol.) were 80 and 5.5, respectively (strawberry), and 91 and 6.8, respectively (lettuce). Strawberry yield was highest in R2 with all fertilized treatments yielding higher than the control. Leaf phosphorus (P) was comparable in all treatments, with R2 giving the highest P content. Lettuce yield was comparable in all treatments. Leaf NO3‐N was higher in all fertilized treatments than the control and leaf P was comparable among all treatments. The lower rate of litter is recommended as it is equally effective to AN and the higher litter rate.

ISSN:0010-3624    

DOI:10.1080/00103629809369935

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Soil columns were produced by filling PVC tubes with a Dark Red Latosol (Acrortox, 22% of clay). A compacted layer was established at the depth of 15 cm in the columns. In the compacted layer, soil was packed to 1.13, 1.32, 1.48, and 1.82 Mg kg‐1, resulting in cone resistances of 0.18, 0.43, 1.20, and 2.50 MPa. Cotton was cropped for 30 days. Lime was applied to raise base saturation to 40, 52, and 67%. The highest base saturation caused a decrease in phosphorus (P) and zinc (Zn) concentrations in the plants. A decrease in root dry matter, length and surface area was also observed. This could be a consequence of lime induced Zn deficiency. Root growth was decreased in the compacted layer, and complete inhibition was noticed at 2.50 MPa. Once the roots got through the compacted layer, there was a growth recovery in the bottom layer of the pots. The increase in base saturation up 52% was effective in preventing a decrease in cotton root length at soil resistances to 1.20 MPa. Where the roots were shorter, there was an increase in nutrient uptake per unit of root surface area, which kept the plants well nourished, except for P.

ISSN:0010-3624    

DOI:10.1080/00103629809369936

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The potassium (K) status of 22 soil samples from 12 pedons originating in 6 Pacific Island countries has been investigated by several techniques. The total K contents of the soils studied were found to be low to very low. Use of various methods available for measuring exchangeable cations in soils showed exchangeable K to be dependent on factors such as ionic strength and displacement cation of the extracting solution. The proportions of non‐exchangeable K that are plant available were found to be very low for most soils. Data obtained from quantity/intensity measurements suggest that the soils would be responsive to added K.

ISSN:0010-3624    

DOI:10.1080/00103629809369937

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Soil samples were collected from farms in two enset(Ensete ventricosum)growing regions of Ethiopia and analyzed for plant nutrients. For comparative reasons, soil samples were taken both from fields where enset had been continuously cultivated for several decades and from other fields: annual cropping, grazing, or uncultivated. The results reveal that the enset fields studied had higher soil organic matter contents and better nutritional status than fields used otherwise, not only in the topsoil but also in the subsoil. This indicates more sustainable cultivation with maintained fertility in the enset fields. Possible explanations of this are discussed.

ISSN:0010-3624    

DOI:10.1080/00103629809369938

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A commercially available Cartesian coordinate (gantry style) robot has been programmed to sequentially determine soil/water pH (pHw) using a desk‐top computer, electronic switchbox, pH meter and a bank of five combination electrodes. All movements of the robot together with pHwdata acquisition are orchestrated by the computer. Once the pHwdata has been acquired, it is stored in an array for subsequent transfer to a Laboratory Information Management System.

ISSN:0010-3624    

DOI:10.1080/00103629809369939

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The four studies reported describe tolerance of high manganese (Mn) in solution culture for 164 wheat genotypes. The genotypes were mainly South American, Australian, and CIMMYT in origin. The aims were to identify sources of tolerance of Mn, to assess the possibility of breeding for tolerance, and to identify any mechanism of tolerance. Fourteen genotypes were tolerant of the highest stress used in our experiments (either 2184 or 3276 μM Mn in solution). These genotypes were from Australia, Mexico, Brazil, Chile and other South American countries. They did not display toxicity symptoms and their total dry matter yields were not reduced on exposure to Mn in solution culture. Conversely, the very sensitive cultivar, Teal, had yield reductions up to 87%. The mechanism of tolerance appeared to be internal tissue tolerance. Tolerant genotypes in Experiment 1 accumulated high concentrations of Mn in leaves (1961 μg kg‐1) and roots (3202 μg kg‐1) with no ill effects. The tolerance character appeared to be simply inherited, because it was readily traced through tolerant genotypes which were related. Where toxic effects of Mn were induced, shoot concentrations of calcium (Ca), potassium (K), and magnesium (Mg) were lowered and root/shoot weight ratios were decreased because of greater decrease in root weight than shoot weight.

ISSN:0010-3624    

DOI:10.1080/00103629809369940

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

A growth model has been developed for warm‐season perennial grasses which relates seasonal distribution of dry matter to calendar time through the probability equation, and which relates total seasonal dry matter to harvest interval through a linear‐exponential equation. The model is used to describe response of ‘Tifton‐9’ bahiagrass(Paspalum notatumFlögge) to time and harvest interval at Quincy, FL. It is also shown that yield response to applied nitrogen (N) is described by the logistic equation, in agreement with earlier results for bahiagrass and other forage grasses. This model removes the restriction of harvest interval to 6 or 7 wk of the previous linear growth model. Maximum dry matter yield exceeded 20 Mg ha‐1. Maximum incremental dry matter response to applied N occurred at approximately 140 kg N ha‐1. A harvest interval of 8 wk provided peak dry matter production. The mean and standard deviation of dry matter distribution were 28.5 wk and 6.0 wk, respectively. Correlation coefficients of the models with data exceeded 0.99. Effects of harvest interval and applied N are easily accounted for with this model, which uses analytical functions and avoids the need for finite difference techniques.

ISSN:0010-3624    

DOI:10.1080/00103629809369941

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

ISSN:0010-3624    

DOI:10.1080/00103629809369923

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor