Increased eutrophication and nutrient imbalances in the agricultural soil of NE Catalonia, Spain.

The soil C, N, P and K content of agricultural soil were measured over the last 4 decades in NE Catalonia (NE Spain). Plant-available P and K increased by ca 109 and 105% respectively and total N decreased by 30%. The increases in plant-available P content are in accordance with the increasingly used pig slurry being very rich in P, and with P tendency to be retained in soils, since it is less mobile than N. The total soil N (Ntot) decrease occurred in the first decade (by 41%). The uptake and withdrawal of mineral N by crops and the leaching of mineral N into groundwater and rivers after torrential rainfalls were the two likely major pathways of N-loss from the soil. After the first decade, there has been no further decrease of Ntot as a result of the increasing fertilization of these fields, including the increasing applications of pig slurry. These results show an increasing P eutrophication in Mediterranean agricultural soils and will have several consequences for the next decades with (i) an increasing unbalance between N and P (and K) in soils that might affect crop productivity, (ii) an increasing leaching of N as nitrate to continental waters, both ground and surface waters, and (iii) a consequent need for the establishment of another fertilization strategy based on lowering the use of pig slurry and on increasing the use of fertilizers of slow mineralization that increase soil organic matter, and stabilise the soil N and P contents.

Root-surface phosphatase activity in shrublands across a European gradient: effects of warming.

Root-surface phosphatase activities were measured in natural and semi-natural shrublands across an European climatic gradient of temperature and rainfall including Wales (WL), Denmark (DK), Netherlands (NL), Hungary (HU), Italy (IT) and Spain (SP). In each site a warming experiment was conducted since 1999 or 2001 by means of passive night-time warming using reflective curtains that covered the vegetation at night. The treatments increased yearly average soil temperatures around 0. 8 degrees C in most of sites. Root-surface phosphatase activity values ranged between 56 mg PNP g(-1) h(-1) in IT and 3.5 mg PNP g(-1) h(-1) in HU. Warming had no effect on root-surface phosphatase activity across the sites and only in Hungary a slight increase was detected. Plants at Mediterranean sites (IT, SP) showed a higher root-surface phosphatase activity than plants at temperate sites (WL, NL, DK). We suggest it might be an adaptation of plant species evolved under Mediterranean climate that allows them a) to compensate in wet period for the decrease in phosphatase activity, and thus P uptake, during drought periods, and/or b) to benefit from soluble organic P flushes following the frequent drying-rewetting episodes experienced by soils in Mediterranean ecosystems.