Long-Term Soil Ecosystem Studies

Water quality changes and biogeochemical development were evaluated over 2 years in two newly created freshwater riparian wetland ponds (1 ha each) in an agricultural and urban watershed. Both wetlands received pumped river water and had similar hydrologic regimes. One wetland was planted with 13 species of vegetation typical of Midwestern US marshes; the other received no planted vegetation. Water quality sampling was conducted weekly and detailed hydrologic budgets were developed from data collected twice daily. Hydrologic budgets were dominated by pumped surface flows (mean inflow1480 m3 day1). Two floods accounted for 32% of inflow in 1 year. Both wetlands significantly decreased turbidity (62 to 27 NTU) and increased dissolved oxygen (9–11 mg l1). Inflow dissolved reactive phosphorus (DRP) and total phosphorus (TP) concentrations (1793 and 169911 mg P l1) were significantly higher (PB0.05) than outflow concentrations (DRP: 591 and 691 mg P l1; TP: 6998 and 7499 mg P l1) for planted and unplanted wetlands, respectively. Phosphorus removal was related to decreases in turbidity and the level of biological activity. Extensive and highly productive algal coverage in both wetlands and the subsequent deposition and decomposition of the algal mat influenced P retention through biological uptake and chemical sorption and coprecipitation. Mean removal rates were 1.0 g P m2 year1 for DRP and 5.4 g P m2 year1 for TP and did not differ significantly between wetlands (PB0.05). Approximately 35% of TP mass removal occurred during two floods. A conservative tracer (Cl) indicated limited and negligible effects of dilution on decreases in P concentration. Water flow rate and P concentration did not affect P removal which was loading-limited and seasonal. Initial development of macrophytic vegetation demonstrated no influence on water quality changes. Both wetlands acted as effective P sinks in the initial 2 years of operation. © 2000 Elsevier Science B.V. All rights reserved.

Soil samples from a 32-year grassland field experiment were taken from 0–5, 5–10, and 10–15 cm soil depths in February 2002. Plots received annual treatments of unamended control, mineral fertilizer, three rates of pig slurry and three rates of cow slurry, each with six replicates. Samples were analysed for cation exchange capacity (CEC), exchangeable cations (Naþ, Kþ, Ca2þ, Mg2 þ), pH and Olsen P. Exchangeable sodium percentage (ESP) was calculated as a sodicity indicator. Mean ESP was generally greater for slurry treatments than the control, with a trend of increasing ESP with application rate. This was particularly marked for cow slurry. At 0–5 cm depth ESP increased from 1.18 in the control to 1.75 at the highest rate of pig slurry and 5.60 at the highest rate of cow slurry. Similar trends were shown for CEC, exchangeable Naþ, Kþ and Mg2þ, Ca2þ and Olsen P. The build-up of soil P due to slurry applications, together with this combination of physical and chemical factors, may increase the risk of P loss to surface waters, particularly from soils receiving high rates of cow slurry.

The responses of tallgrass prairie plant communities and ecosystem processes to fire and grazing are well characterized. However, responses of invertebrate consumer groups, and particularly soil-dwelling organisms, to these disturbances are not well known. At Konza Prairie Biological Station, we sampled soil macroinvertebrates in 1994 and 1999 as part of a long-term experiment designed to examine the effects and interactions of annual fire, mowing, and fertilization (N and P) on prairie soil communities and processes. For nearly all taxa, in both years, responses were characterized by significant treatment interactions, but some general patterns were evident. Introduced European earthworms (Aporrectodea spp. and Octolasion spp.) were most abundant in plots where fire was excluded, and the proportion of the total earthworm community consisting of introduced earthworms was greater in unburned, unmowed, and fertilized plots. Nymphs of two Cicada genera were collected (Cicadetta spp. and Tibicen spp.). Cicadetta nymphs were more abundant in burned plots, but mowing reduced their abundance. Tibicen nymphs were collected almost exclusively from unburned plots. Treatment effects on herbivorous beetle larvae (Scarabaeidae, Elateridae, and Curculionidae) were variable, but nutrient additions (N or P) usually resulted in greater densities, whereas mowing usually resulted in lower densities. Our results suggest that departures from historical disturbance regimes (i.e. frequent fire and grazing) may render soils more susceptible to increased numbers of European earthworms, and that interactions between fire, aboveground biomass removal, and vegetation responses affect the structure and composition of invertebrate communities in tallgrass prairie soils. q 2003 Elsevier Science Ltd. All rights reserved.

The rice (Oryza sativa L.)-wheat (Triticum aestivum L.) cropping system occupies about 13.5 million ha in South Asia and is important for the region's food security. We examined the long-term yield trends, changes in soil nutrient fractions (both total and available), and nutrient balances in a 20-yr rice-rice-wheat experiment conducted in the Indo-Gangetic plain of Nepal. The yield of first rice crop fertilized with recommended NPK fertilizer or farmyard manure (FYM) declined an average of 0.09 or 0.07 Mg ha(-1) yr(-1), respectively. These 20-yr trends explained only 20 to 21% of the variability in yield, and inexplicable shorter-term yield trends were observed. Likewise, wheat yield declined at 0.05 Mg ha(-1) yr(-1) (with both NPK and FYM) over the 20 yr. However, the yield of second rice crop did not decline over that period. The total and available N and P, and total and labile C contents of soil from Year 10 to 20 were either maintained or increased, but total K and available K declined. The apparent K balance showed net losses of 62.3 and 15.2 kg K ha(-1) yr(-1) with NPK and FYM treatments, respectively. Depletion of soil K and inadequate K fertilization seems to be the primary reasons of limited and declining yield of first rice and wheat crop. In addition, the yield of wheat declined because of a delay in sowing, which was estimated to be 0.04 Mg ha(-1) for each day delay in sowing. The study showed that the current local fertilizer recommendations, particularly for K, for the rice-rice-wheat system are inadequate.

The effect of annual banding of superphosphate (0-45 kg P ha(-1)) on soil phosphorus (P) content, growth, and yield of wheat was investigated from 1982 to 1998 in a major rainfed wheat production area of South Africa. Conventional tillage practices in a wheat monoculture cropping system were followed under summer rainfall conditions. The responses of wheat growth to fertilizer P application were evident during early and late tillering growth stages, with decreased responses towards maturity. Although average yields varied between cropping seasons (0.881 to 3.261 t ha(-1)) due to climatic conditions, significant exponential response patterns between yield and fertilizer P applications existed. Optimum yields were achieved with P applications of 10 to 15 kg P ha(-1). The recovery of fertilizer P in the grain decreased with increasing P applications. Results of soil P analyses and calculated P balance indicated a more rapid increase in soil P content with application of fertilizer P at levels above 20 kg P ha(-1), with gradual increases occurring at lower levels.

The long-term effects of Yearly fertilizer applications on soil chemical properties and nutrient availability are not well documented for cassava (Manihot esculenta) production in Vietnam. In 1990, research plots were established (randomized complete block design) with 12 treatments to test effects of different rates of N, P and K on soil properties in Acrisols (FAO-UNESCO Soil Classification) at Thai Nguyen University, North Vietnam. In June 1998, composite soil samples (0- to 10-cm and 10- to 20-cm depth) were collected from each plot. Nine years of N application significantly reduced the labile pools of soil inorganic P, total soil P and soil extractable K and Mg. Total soil N was only slightly increased in the 10- to 30-cm depth. Long-term applications of P significantly increased soil inorganic P fractions, but reduced concentrations and supply rates of nitrate and K. Moreover, 9 yr of K application significantly increased soil organic C (two depths), soil total N (10-30 cm) and soil extractable K in the 0- to 10-cm depth. Generally, the results show that long-term applications of mineral fertilizers in a ratio of N:P2O5:K2O of 2:1:2 (at the rates of 80 N:40 P2O5:80 K2O or 160 N: 80 P2O5:160 K2O) are effective in maintaining the total content and availability of applied nutrients, but when applied alone are associated with decreases in other nutrients.

External phosphorus (P) fertilization in intensive cropping systems often exceeds P demand by crops, which leads to P accumulation in soils. Levels of different pools of soil P have been affected not only by soil properties and climatic condition but also by rate and type of P applied. This experiment was conducted to investigate the long-term applications of compost and chemical fertilizer on soil phosphorus status in paddy cropping system after addition of compost and chemical fertilizers for 34 years in rice monoculture production at National Youngnam Agricultural Experiment Station, Miryang, Korea. Four different treatments of soil amendments were selected in this study: control, compost application, NPK (nitrogen– phosphorus–potassium) fertilizer application, and compost plus NPK fertilizer application. Phosphorus status varied with the longterm applications of compost and fertilizers, and the compost plus NPK fertilizer treatment significantly increased total P in soil. Available P was increased in the treatments that received chemical fertilizers. Applications of compost and chemical fertilizers increased organic P fraction but the ratio of organic P to total P declined with application of compost or chemical fertilizers. Phosphorus-fixation was significantly increased due to the long-term application of compost and chemical fertilizers. The P fixation was highest with iron (Fe) than with aluminum (Al) and calcium (Ca) in the paddy soil. The highest Fe-P content occurred in the compost plus NPK fertilizer treatment. These results represented that the higher level of P remaining in the soil is accumulated by long-term annual application of compost and chemical fertilizers than by that of chemical fertilizer, and P accumulation might be a gradual saturation of the P-sorption capacity.