Evaluation of phosphorus placement methods and nitrogen carriers under conditions of maize bean intercropping : summary

Meeting: Symposium on Intercropping in Semi-Arid Areas, 2d, 4-7 Aug. 1980, Morogoro, TZIn IDL-391

Evaluation of soil testing methods for available potassium in some soils of Morogoro

Meeting: Symposium on Intercropping in Semi-Arid Areas, 2d, 4-7 Aug. 1980, Morogoro, TZIn IDL-391

Green Manure and inorganic Fertiliser as Management Strategies for Witchweed and Upland Rice

Weed infestation, especially the Witchweed ( Striga asiatica ) is a serious problem in fertility-depleted soils of Tanzania. The use of urea fertiliser is known to control weed but resource-poor farmers cannot afford this technology due to high costs involved. To alleviate the problem of Striga and soil fertility, green-manure applications could be an alternative strategy. Ths study was conducted to (a) evaluate the potential of green manure against Striga, and (b) determine the potential of inducing Striga suicidal germination by selected green manures. For the first part of the study, treatments included three green manure species, Crotolaria ochlroleuca G. (sunhemp), Mimosa invisa L.(Colla) and Cassia obtusifolia L.(Sicklepod) superimposed with three fertiliser rates 0, 25 and 50 kg N ha-1. The treatments were laid out in a randomised complete block design (RCBD). In the second study part, the 3 green manure species were evaluated for their potential to stimulate Striga seed germination in the laboratory and the field. Results showed that green manure applications significantly reduce Striga infestation, resulting in significant rice yield increases. Green manure exhibited potential to induce suicidal germination of Striga. Based on these findings, green manure applications should be promoted especially among smallholder resource-poor farmers as a strategy for control of Striga infestation in rice fields. Additionally, crop rotation using rice and C. ochlroleuca is the best option since it reduces Striga infestation and increases yield of rice.Désherber l'infestation surtout de witchweed ( Striga asiatica ) est un problème sérieux dans les sols de fertilité réduite de Tanzanien. L'usage de l'urée est connu pour contrôler les mauvaises herbes mais les agriculteurs avec les ressources pauvres ne peuvent pas se permettre ces technologies en raison des hauts coûts impliqués. Pour alléger le problème de de Striga , les applications de fumier vert pourraient être une stratégie alternative. Cette étude a été dirigée pour (a) évaluer le potentiel de fumier vert contre Striga, et ( b) déterminer le potentiel d'induire la germination suicidaire de Striga pour des fumiers verts choisis. Pour la première partie de l'étude, les traitements ont inclus trois espèces de fumier verte, Crotolaria ochlroleuca G. (Sunhemp), le Mimosa invisa L. (Colla) et Cassia obtusifolia L. (Sicklepod) a superposé avec trois taux d'engrais 0, 25 et 50 kg N ha-1. Les traitements ont été faits dans une conception des blocs complètement aléatoire (RCBD). Dans la deuxième partie d'étude, la 3 espèce de fumier verte a été évaluée pour son potentiel de stimuler la germination de semence de Striga dans le laboratoire et le champ. Les résultats ont montré que l'application de fumier vert réduit significativement l'infestation de Striga, avec comme résultat des augmentations de rendement de riz significatives. Le fumier vert a exposé le potentiel pour induire la germination suicidaire de Striga. A la lumière de ces résultats l'application de fumier vert devrait être surtout promues parmi le petit exploitant agriculteurs pauvre comme une stratégie de contrôle d'infestation de Striga dans les champs de riz. En plus, la rotation de récolte utilisant du riz et C. ochlroleuca est la meilleure option puisque il réduit l'infestation de Striga et augmente le rendement de riz

Copper availability as related to soil copper fractions in oxisols under liming Calagem e os teores disponíveis e as frações de cobre em latossolos

The knowledge of the chemical forms of copper in soils and the relationships of these forms with soil copper availability are important for predicting the copper behavior in the soil-plant system. The present work studies the influence of liming on the available contents of copper as well as on the forms of copper fractions in six types of Oxisols. Soil samples, with and without liming, received copper at rates of 0.0, 20.0 and 40.0 mg dm-3 and remained incubated for 30 days. Then, available copper was extracted with Mehlich-1, Mehlich-3, DTPA and EDTA solutions, and analyzed by atomic absorption spectrophotometry. Additionally, soil samples were extracted in a sequential procedure to determine Cu in fractions of soil, as follows: exchangeable-Cu fraction, organic matter-Cu fraction, Mn oxide-Cu fraction, amorphous Fe oxide-Cu fraction, crystalline Fe oxide-Cu fraction, residual-Cu fraction, and the total Cu content in the soil. Soil samples to which Cu was added presented higher Cu retention in the organic matter fraction with a small percentage retained in the exchangeable-Cu fraction. Liming resulted in a decrease of Cu in the exchangeable and organic matter fractions and an increase in the Fe and Mn oxide fractions and in the residual fraction. Without liming, the organic matter fraction presented the highest contribution to Cu content found in the soil extracts obtained with all extractors, except EDTA. For treatments with liming, Cu contents in the organic matter fraction were better correlated to Cu contents in extracts obtained with DTPA and Mehlich-3.<br>O conhecimento das formas químicas em que se encontra o cobre em solos, e suas relações com os teores disponíveis, são importantes para a previsão do seu comportamento no sistema solo-planta. Nesse sentido, este trabalho estuda a influência da calagem sobre os teores disponíveis e sobre o fracionamento de Cu em amostras de seis Latossolos. Essas amostras, submetidas ou não a calagem, receberam o elemento nas doses de 0,0, 20,0 e 40,0 mg dm-3 e foram incubadas por 30 dias. Terminada a incubação, procedeu-se a extração de Cu utilizando-se os extratores Mehlich-1, Mehlich-3, DTPA e EDTA. As amostras foram submetidas a um fracionamento que separou o Cu nas frações trocável, matéria orgânica, óxido de manganês, óxido de ferro amorfo, óxido de ferro cristalino e residual, além dos teores totais. Com sua aplicação ao solo o Cu foi retido, principalmente, na fração matéria orgânica, com pequena porcentagem retida na fração trocável. A calagem provocou redução nas frações trocável e matéria orgânica e aumento nas frações óxido de ferro, óxido de manganês e residual. Para os solos sem calagem, a fração matéria orgânica foi a que mais contribuiu para os teores determinados pelos extratores, com exceção do EDTA. Nos solos com calagem, o Cu ligado à matéria orgânica foi melhor correlacionado com os teores obtidos pelo DTPA e Mehlich-3

Assessing potential dietary toxicity of heavy metals in selected vegetables and food crops

Heavy metals, such as cadmium, copper, lead, chromium and mercury, are important environmental pollutants, particularly in areas with high anthropogenic pressure. Their presence in the atmosphere, soil and water, even in traces can cause serious problems to all organisms, and heavy metal bioaccumulation in the food chain especially can be highly dangerous to human health. Heavy metals enter the human body mainly through two routes namely: inhalation and ingestion, ingestion being the main route of exposure to these elements in human population. Heavy metals intake by human populations through food chain has been reported in many countries. Soil threshold for heavy metal toxicity is an important factor affecting soil environmental capacity of heavy metal and determines heavy metal cumulative loading limits. For soil-plant system, heavy metal toxicity threshold is the highest permissible content in the soil (total or bioavailable concentration) that does not pose any phytotoxic effects or heavy metals in the edible parts of the crops does not exceed food hygiene standards. Factors affecting the thresholds of dietary toxicity of heavy metal in soil-crop system include: soil type which includes soil pH, organic matter content, clay mineral and other soil chemical and biochemical properties; and crop species or cultivars regulated by genetic basis for heavy metal transport and accumulation in plants. In addition, the interactions of soil-plant root-microbes play important roles in regulating heavy metal movement from soil to the edible parts of crops. Agronomic practices such as fertilizer and water managements as well as crop rotation system can affect bioavailability and crop accumulation of heavy metals, thus influencing the thresholds for assessing dietary toxicity of heavy metals in the food chain. This paper reviews the phytotoxic effects and bioaccumulation of heavy metals in vegetables and food crops and assesses soil heavy metal thresholds for potential dietary toxicity