摘要:

Self-sustaining, diversified, highnetyielding, economically viable agriculture, integrating aesthetic, ethical, conservation and recreational needs with food production is termed Ecological Agriculture; the criteria of which are outlined. Whether such a system could work in a marginal area is the subject of this paper.

ISSN:0144-8765    

DOI:10.1080/01448765.1991.9754551

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The present work was undertaken to evaluate the influence of three cucurbit food plants,Lagenaria vulgaris, Luffa cylindricaandCucurbita maximaon the behaviour of and sex allocation by the female parasitoidTrioxys indicusat varying densities on its hostAphis gossypii.Food plant species and parasitoid density did not influence the percentage emergence of the parasitoid from mummies; however, both had a significant influence on the total number of mummies yielded or adults which emerged. Increasing parasitoid density decreased the searching efficiency of the parasitoid on each food plant fed host. The values of the interference constantmwas higher onL. cylindricaandC. maxima-fed hosts than onL. vulgaris-fed hosts which decreased the searching efficiency of the female on those food plants. K-values for mortality due to parasitism were lower onL. cylindricaandC. maximafor all parasitoid densities. More than 50% diploid eggs were deposited in the hosts feeding onL. vulgaris(54.5–67.8%) andL. cylindrica(50.3–70.3%) whereas only 35.5 to 46.9% were deposited in the hosts feeding onC. maxima.The results demonstrated a significant effect of the food plants on the performance of the parasitoid and therefore food plants should also be considered as an important factor in biological control programmes.

ISSN:0144-8765    

DOI:10.1080/01448765.1991.9754552

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The solubilization and availability of phosphorus were measured during decomposition of wheat straw and cattle urine with two types of low grade rock phosphate, Mussoorie rock phosphate (M. phos) and Hyperphos. The rate of solubilization of insoluble phosphorus from both M. phos and Hyperphos increased significantly up to 60 days and thereafter decreased with increasing decomposition time. Molasses incorporation enhanced solubilization throughout the decomposing period of 120 days; it reached a maximum of 24.5 and 14.7% of the added insoluble phosphate for both M. phos and Hyperphos, respectively. About 95 to 99% of the solubilized P was converted into organic forms. In view of very high turnover of organic P, the availability of solubilized P was measured by fractionating organic P (Po) substrates. In the presence of both rock phosphates, with or without addition of molasses, organic Po was redistributed between 4–6, 68–72, 12–16 and 10–12% in labile, moderately labile, moderately resistant and highly resistant fractions respectively at 120 days of composting. M. phos solubilized more readily and retained a greater amount of labile and moderately labile Po than Hyperphos.

ISSN:0144-8765    

DOI:10.1080/01448765.1991.9754553

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The effect on weeds and crop yield of a short-term polypropylene cover as a protection against carrot fly (Psila rosae) damage to organically grown carrots was assessed. Crops were hand-weeded prior to cover and then subjected to one of three weeding treatments during the covered period: none, one or two weedings. Total weed weight was greater with covered, versus non-covered, plots only for the one-weeding treatment. No-weeding treatments had the highest total weight of weeds, with no difference between one-or two-weedings, whether plots were covered or not. Three weeds were more frequent (as estimated by approximate cover) and taller under cover:Capsella bursa-pastoris, Hypochaeris radicataandPolygonum convolvulus.Covering the crop did not significantly increase carrot yield. Yield was lower for the no-weeding treatments, yet weeding more than once did not increase yield. Based on these and similar results, assessments are made on the weed response to short-term covering and the use of this cover by organic growers.

ISSN:0144-8765    

DOI:10.1080/01448765.1991.9754554

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The effect of different initial numbers of the host,Rhopalosiphum maidis, on the demographic statistics of its parasitoid,Lysiphlebus delhiensis(Subba Rao & Sharma), was determined under constant laboratory conditions. The survival rate (lx) of the female parasitoid was unaffected by host density, with an average adult life-span of 7.2 days at 20 ± 1°C. The age specific fecundity rate (mx) was host density-dependent. The value of mxdecreased rapidly from the first day of oviposition until the death of the female. Fecundity was highest with an average of 270.8 ± 35.9 SD mummies/female at 200 hosts/cage (30 × 30 × 45 cm); the maximum number of mummies yielded by any female was 304. The relationship between host density and the number of aphids parasitised per female was linear at ≤50 aphids/cage/day but at higher host densities (≥ 100 aphids/cage/day) a significant curvilinear regression was observed. The intrinsic rate of natural increase (rm) increased with increasing host density. Maximum value of rm(0.31 females/female/day) was obtained at 200 hosts/cage. The response of rmto variations in host density and parasitoid sex ratio is shown.

ISSN:0144-8765    

DOI:10.1080/01448765.1991.9754555

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Green manuring with vetch was evaluated on an acid soil in the highland region of Rwanda, East-Central Africa. Incorporation of 5-month old vetch lowered soilpH as well as raising exchangeable Al and H and reducing exchangeable Ca, Mg, and P. Consequently, bean and wheat yields for the subsequent season were reduced by 71 and 33%, respectively. There was no response to fertilizer N on either main treatment. There were no significant yield differences for either crop with respect to vetch treatment during the second season. Third season crop yields were superior on the control plot, with that of beans being significantly different. Application of lime raised exchangeable Ca, K, ECEC and reduced exchangeable A1. Bean was more affected by exchangeable A1 than wheat. Half-life for decomposition of the vetch was 3.5 weeks and nutrient release pattern followed the order: K>N>P>Caindicating that liming may be required to supply Caand to neutralize soil acidity at the initial stages of decomposition.

ISSN:0144-8765    

DOI:10.1080/01448765.1991.9754556

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0144-8765    

DOI:10.1080/01448765.1991.9754557

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0144-8765    

DOI:10.1080/01448765.1991.9754558

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0144-8765    

DOI:10.1080/01448765.1991.9754559

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0144-8765    

DOI:10.1080/01448765.1991.9754560

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor