Dissolution of different zinc salts and Zn uptake by Sedum alfredii and maize in mono-and co-cropping under hydroponic culture

Previous soil pot and field experiments demonstrated that co-cropping the hyperaccumulator Sedum alfredii with maize increased Zn phytoextraction by S. alfredii and decreased Zn uptake by maize shoots. This hydroponic experiment was conducted to investigate whether the facilitation of Zn phytoextraction by S. alfredii resulted from improved dissolution in this co-cropping system and its relation to root exudates. S. alfredii and maize were mono-and co-cropped （without a root barrier） in nutrient solution spiked with four Zn compounds, ZnS, ZnO, Zn3（PO4）2 and 5ZnO·2CO3·4H2O （represented as ZnCO3 ） at 1000 mg/L Zn for 15 days without renewal of nutrient solution after pre-culture. The root exudates were collected under incomplete sterilization and analyzed. The results indicated that the difference in Zn salts had a greater influence on the Zn concentration in maize than for S. alfredii, varying from 210-2603 mg/kg for maize shoots and 6445-12476 mg/kg for S. alfredii in the same order： ZnCO3 〉 ZnO 〉Zn3（PO4）2 〉 ZnS. For the four kinds of Zn sources in this experiment, co-cropping with maize did not improve Zn phytoextraction by S. alfredii. In most cases, compared to co-cropped and mono-cropped maize, mono-cropped S. alfredii resulted in the highest Zn2＋ concentration in the remaining nutrient solution, and also had a higher total concentration of low molecular weight organic acids （LMWOA） and lower pH of root exudation. Root exudates did partly influence Zn hyperaccumulation in S. alfredii.

Overview of farming practices in the water-logged areas of Kerala, India

Water logging is one of the major problems of land degradation in India.Unscientific management of soil,water and crops in irrigated lands,and obstruction of natural drainage systems by various developmental activities are the main factors responsible for disrupting the balance of inflow and outflow of water,leading to water stagnation.While irrigation has increased by leaps and bounds,its attendant problem of water logging is now plaguing substantial area of agricultural lands.The low-lying areas of Kerala,the southernmost state of India,are potential areas of paddy production.But these areas are situated below the mean sea level and have serious problems of water-logging.About twenty five percent of total paddy lands in Kerala are water-logged;especially in Kuttanad,Pokkali,Kole and Kaipad areas.An integrated rice-shrimp/prawn farming are practiced in these areas.One rice crop followed by shrimp/prawn capture provides a substantial subsidiary income to the farmer.The major issues faced in these areas are mainly related to pollution,eutrophication,encroachment,reclamation,mining and biodiversity loss.As a result of denuding,polluting,draining,filling,etc.,these water-logged areas have been under severe threat.The potentiality of these areas should be exploited and necessary measures in conserving these areas need to be undertaken.Sustainable farming where a judicious mix of integrated enterprise concept of resource based planning based on public participation is slowly developing in these areas.A clear perspective and a management system that ensures participation and regulation in resource use are essential.