Study On Characteristics Of Achnatherum Splendens Tussock Fertile Island

The Achnatherum splendens tussock in oasis-desert ecotone in Tianzhu Countyof Gansu Province was used to study the characteristics of fertile island through fieldobservation and surveys, sampling and sample analysis in lab in order to explore thedynamics of soil nutrients in different developmental stages, reveal the fertile islandformation mechanism and its variation, and then to provide a reliable basis ofgrassland rational utilization and restoration in research area.The results showed that soil nutrient contents within tussock canopy were higherthan those outside the canopy. The enrichment effect of fertile island reduced with theincrease of soil depth and distance from the grass center. And it was enhanced withthe expanding of fertile island size, the enrichment patterns of different soil nutrientsdiffered and the correlation among soil nutrients enhanced with the expading of fertileisland size.Along with the expanding of fertile island size, the soil nutrient enrichment oftussock at different development stages showed the following patterns from the islandcenter to100m away:1) pH value: There was no obvious variation pattern within0-30cm soil layer,and it was lower at island center.2) Organic matter: It was enriched within0-20cmsoil layer and then stable for small fertile island. For middle fertile island, The contentdecreased first and then increased within0-20cm soil layer, while in20-30cm soillayer, it decreased and then remained stable. For large fertile island, it wassignificantly enriched in0-30cm soil layer, and decreased first and then increased.3)Total nitrogen: It showed a same pattern with organic matter for small fertile island.For middle and large fertile islands, the content first decreased and then increased in0-30cm soil layer.4) Total phosphorus: It also showed a same pattern with organicmatter for small fertile island. Its content decreased first and then kept stable in0-30cm soil layer for middle fertile island. And it reduced first and then increased in0-30cm soil layer for large fertile island.5) Total potassium: Its content varied and no obvious pattern was found.6) Available nitrogen: It was enriched in0-20cm soillayer of small fertile island, and in0-30cm soil layer for middle fertile island, andthen decreased and then remained stable. For large fertile island, it was significantlyenriched in0-30cm soil layer and then gradually reduced.7) Available phosphorus: Itwas enriched in0-20cm soil layer and then reduced and stable for small fertile island.For middle fertile island, it was enriched in0-30cm soil layer, and reduced and thenincreased. For large fertile island, it continuously reduced in0-30cm soil layer.8)Potassium: The content in0-10cm soil layer was2to3times of those in10-20cmand20-30cm layers. It was enriched in0-20cm soil layer for small fertile island anddecreased and then increased. For middle fertile island, it was enriched in0-20cm soillayer and decreased first and then increased. while in20-30cm soil layer, it firstdecreased and later remained stable. For large fertile island, it kept decreasing in0-30cm soil layer.9) Available copper: it did not show obvious variation patterns.10)Available manganese: It was enriched in0-20cm soil layer and then reduced andstable for small fertile island. For middle fertile island, it was enriched in the0-30cmsoil layer, and reduced and then increased. For large fertile island, it continuouslyreduced in0-30cm soil layer.11) Available zinc: Its content reduced first and thenkept stable in0-20cm soil layer for small and middle islands. For large island, itdecreased and then increased in0-20cm soil layer and it kept stable in20-30cm soillayer.12) Available iron: No obvious variation patterns were found for small fertileisland. it first reduced and then remained the same in0-20cm soil layer for middlefertile island, while it decreased and then increased in20-30cm soil layer. For largefertile island, it first decreased and then increased in0-30cm soil layer.Along with the expanding of fertile island, the pH gradually decreased; organicmatter, total nitrogen, total phosphorus, manganese, available, available zinc,available iron contents increased first and then reduced, and nutrients in center area ofsmall fertile island were higher than those of large ones. Total potassium contentgradually increased while available copper had no obvious variation pattern. In0-30cm soil layer, the correlation of soil nutrients between the center of all fertileislands were growing, pH and available copper in various developmental stages of the fertile island showed a significant positive correlation (P <0.01), while pH andavailable copper with other nutrients were negatively correlated. Differentdevelopmental stages of grasscluster center in the0-30cm soil, pH and availablecopper showed a highest correlation, and as well as available nitrogen and organicmatter and total nitrogen; The absolute value of total potassium and potassiumcorrelation, total phosphorus and available phosphorus correlation was the highest.