摘要:

Nassella tussock (Stipa trichotomaNees.) has a high annual production of seeds per plant. The total seed bank of all plants counted under a dense nassella infestation varied between 50 000 and 100 000 seeds m−2surface area (5 cm deep) of which more than half were nassella. Seeds were recovered from soil samples by wet-sieving, chemical flotation and aspiration. Burning of the dead organic material on the soil surface destroyed about 20% of the nassella seeds present in the top layers, suggesting that this treatment could become a useful part of a control strategy.S. Afr. J. Plant Soil1984, 1: 1–3

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634099

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor

摘要:

Voandzeia subterraneaandCajanus cajanare important pulse crops in tropical and subtropical Africa and their drought hardiness and ability to utilize poor soils areinter aliareasons for this popularity. Both species hold considerable promise as crops in South Africa. The results of a pot trial and a field trial in which the responses of these two species to lime, phosphorus and potassium applications were compared with those ofVigna unguiculata, V. radiataandArachis hypogaeaare reported.The generally held belief that C.cajanis able to produce well with a minimum of fertilizer was confirmed in this investigation, particularly in the field trial where no yield responses to applications of lime, phosphorus and potassium could be measured on a rather poor soil.V. subterranea, on the other hand, responded better, particularly to lime application. Contrary to what is generally claimed in the literature, there was no indication thatV. subterraneais able to produce better than the common groundnut (A. hypogaea) at low levels of soil fertility. In fact, it has to be concluded from the results that this species is not as tolerant to acid soils as the common groundnut.S. Afr. J. Plant Soil1984, 1: 4–8

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634100

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor

摘要:

Cabbage (Brassica oleraceavar.capitata f. albacv. Gloria Osena) yields were measured in two experiments on a Westleigh soil near Pietermaritzburg in response to different methods, rates and times of application of nitrogen fertilizer.Levels ranging from 0–375 kg N ha−1were tested. The result was an almost linear increase in yield with increasing nitrogen up to the highest level applied in the first trial. In the second trial no significant increase in yield was recorded from 75 kg N ha−1up to375 kg N ha−1. In this trial nitrogen applied by banding and broadcasting produced similar results. There was a significantly better yield when half the nitrogen was applied before planting and half four weeks after transplanting, in comparison with all being applied before planting, or one third before planting with two top-dressings and one quarter before planting with three top-dressings.S. Afr. J. Plant Soil1984, 1: 9–11

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634101

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor

摘要:

The well known sigmoidel ET/Ep-curve often quoted in the literature for a variety of crops, merely depicts a smoothed curve drawn through points representing the average ET/Epratio for each depletion cycle co-ordinated with the middle day of the cycle. In this form it is of little use for monitoring the water balance of a crop during periods shorter than a normal irrigation cycle. The seasonal curve can be broken down into a number of separate curves based on the actual ET/Epratios (fi) within each depletion cycle. From these fi-curves, hypothetical curves were derived from which cumulative soil moisture depletion up to a given day within an irrigation cycle can be deduced with ease. This approach provides a way in which the efficiency of rain precipitation can be estimated to a higher degree of accuracy so that the irrigation programme can be adjusted accordingly.S. Afr. J. Plant Soil1984, 1: 12–16

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634102

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor

摘要:

Biotoetse met graansorghum (Sorghum bicolorL.) is in potte in glashuise en groeikabinette uitgevoer. Geselekteerde grond- eienskappe is gekorreleer met alachloraktiwiteit. Organiese materiaalinhoud (% C) was die beste gekorreleerd met die aktiwiteit van alachlor en pH die swakste. Die r-waardes vir % C en kleipersentasie was 0,76 en 0,68 onderskeidelik. In meer- voudige regressie-analises is die grootsteR2-waarde met organiese materiaalinhoud en kleipersentasie verkry. Die effek van grondvog en temperatuur op die aktiwiteit van alachlor is ook ondersoek. By 20/10, 25/15 en 30/20°C dag/nag- temperatuurregimes was alachloraktiwiteit hoog in die grond by veldkapasiteit en versadigingspunt (2×veldkapasiteit), maar laag in lugdroëgrond.S.-Afr. Tydskr. Plant Grond1984, 1: 17–20

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634103

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor

摘要:

Phosphorus considerations are gaining increasing attention where sewage sludges are applied to land because of the continuing trend of rising P levels in sludges and the growing concern for environmental pollution and nutrient recycling issues. P in sludges has reached levels comparable to inorganic fertilizers in some cases while currently average values will be in the region of 2% P (dry solids basis). In reactions with soils the soluble component (or that capable of being solubilized) will be the most important fraction. Potential benefits to be gained from sludge applied P are large while hazards from disposal of sludge P are minimal owing to the transformations which P undergoes in soils. The finite world supply of resource P and the escalating costs of inorganic P fertilizers warrants that further research be directed towards making sludges more acceptable as a source of this nutrient. Unacceptable P pollution of the environment is an added stimulus to effectively dispose of and utilize such wastes simultaneously.S. Afr. J. Plant Soil1984, 1: 21–29

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634104

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor

摘要:

Water based pod extracts of the pod wall material of four soybean cultivars were found to reduce the germination rate of mustard (Sinapis albaL.) seeds. Highly significant differences were also observed in this respect between the different pod extracts.These results indicated the presence of a germination inhibitor in senescent soybean pod walls which might provide some protection against the effects of field weathering of soybean seeds.

ISSN:0257-1862    

DOI:10.1080/02571862.1984.10634105

出版商:Taylor&Francis Group    

年代:1984

数据来源: Taylor