Decreasing the Abundance of effusus on Former Agricultural Lands with Noncalcareous Sandy Soils: Possible Effects of Liming and Soil Removal Alfons J. P. Smolders,1,2,3 Esther C. H. E. T. Lucassen,1 Martijn van der Aalst,2 Leon P. M. Lamers,2 and Jan G. M. Roelofs2

Abstract J. effusus on moist or wet soils seems to be strongly deter- More and more agricultural land in the Netherlands is mined by the Olsen-P concentration in the soil. The resto- becoming available for ecological restoration projects. ration of diverse, species-rich vegetation types on former However, nutrient levels in the top layer of the soils are agricultural lands with a noncalcareous sandy soil will in high because the agricultural lands have been heavily fer- most cases not be possible within a reasonable time span tilized for decades. As drainage ditches are no longer without topsoil removal. Liming might be a valuable addi- maintained when agricultural use ends, the agricultural tional measure to enhance the quality of the soil after top- lands usually become much wetter. As a result, former soil removal, and to prevent mobilization of P to groundwater agricultural soils tend to develop extensive monotonous or surface water. If removal of the topsoil is considered to stands of Juncus effusus, which have little value from an create P limitation, it is important to study P concentra- ecological point of view. In this article, we present the re- tions at various depths to establish the amount of soil that sults of field measurements/observations and experiments has to be removed. to examine the relationship between nutrient availability and J. effusus growth. In addition, we present and discuss Key words: agricultural soil, ecological restoration, results of experiments to study the potential beneficial ef- Juncus effusus, liming, Olsen-P, phosphorus, topsoil fects of liming. Our findings show that the growth of removal.

Introduction mainly for nutrients (Grime 1979), whereas under high In the Netherlands, more and more agricultural land is nutrient availability, competition for light becomes the becoming available for ecological restoration projects. main factor, resulting in the dominance of a few high-yield Instances include areas where heathlands or species-rich species. Because drainage ditches are (intentionally or grasslands had originally been turned into agricultural unintentionally) no longer maintained after agricultural land; in some cases, no more than half a century ago, practice has ended, the former agricultural lands usually which are now becoming available again for so-called eco- become much wetter. In many cases, Juncus effusus L. logical restoration projects. The main objective of such becomes established within the vegetation and frequently projects is in most cases to restore the original oligotro- becomes the dominant species on those former agricul- phic nature (wet and dry heathlands with moorland pools tural lands (Kemmers et al. 2004). At locations where or species-rich grasslands). Nutrient levels in the top layer surface water stagnates on the field, filamentous algae of the soils involved in these projects are high because the become dominant. agricultural lands have been heavily fertilized for decades Juncus effusus is a common species of shallow marshes (Barberis et al. 1996). However, low concentrations of and moist (disturbed) sites. It is a rhizomatous perennial nutrients, P in particular, seem to be a prerequisite for that can form monotonous stands as a result of both vigor- long term coexistence of species (Janssens et al. ous clonal growth and high seed production (Wetzel & 1998). Under low nutrient availability, will compete Howe 1999; Ervin & Wetzel 2001, 2002). Because it is one of the dominant species in seed banks, seed availability is 1 B-WARE Research Centre, Radboud University Nijmegen, Toernooiveld 1, seldom a limiting factor (Thompson & Grime 1979; 6525 ED Nijmegen, The Netherlands 2 Dougall & Dodd 1997; Bekker et al. 1996). Once estab- Department of Aquatic Ecology and Environmental Biology, Radboud Uni- versity Nijmegen, Toernooiveld 1, 6525 ED Nijmegen, The Netherlands lished, its seed production can be enormous. Seeds are 3 Address correspondence to A. J. P. Smolders, email [email protected] very light and the rapid germination and growth of the

Ó 2007 Society for Ecological Restoration International seedlings may result in very efficient colonization (Ervin doi: 10.1111/j.1526-100X.2007.00267.x & Wetzel 2001). The dense tussocks and culms, which

240 Vol. 16, No. 2, pp. 240–248 JUNE 2008 Decreasing the Abundance of Juncus effusus on Former Agricultural Lands may reach a height of 1.5 m, then expand in a circular pat- 1 and 7 years earlier. In addition, samples from the top tern by means of underground lateral rhizomes (Wetzel & layer (0–20 cm) were taken at a large number of reference Howe 1999). A well-established J. effusus population has sites (35 locations), which were all characterized by a well- a highly deleterious effect on the vegetation development, developed biodiverse, oligotrophic vegetation, with only which seems to result especially from shading by the J. a low coverage of Juncus effusus. effusus tussocks (Ervin & Wetzel 2002). At one former agricultural field, soil samples were col- Most former agricultural soils thus develop monotonous lected in 13 subplots (2 years after the topsoil had been stands of J. effusus and therefore have very little value removed). The subplots were characterized by different from an ecological point of view, which is currently a very densities of J. effusus. In each subplot, J. effusus biomass serious problem in ecological restoration projects in the was determined to reveal possible correlations between Netherlands (Sival & Chardon 2003; Kemmers et al. 2004; soil characteristics and J. effusus biomass. Lamers et al. 2005). Frequently, mowing of rushes (several Water and NaCl extracts were made from fresh soil times a year, which is highly expensive) may be effective samples. The remainder of the soil was dried (24 hours at in controlling the growth of J. effusus on relatively 70°C) and ground up after which Olsen-P extracts and nutrient-poor lands (Van der Elst & Thompson 1964; Mc digestates were prepared as described below. Organic Corry & Renou 2003). Experiences with restoration meas- matter content was estimated by the loss on ignition at ures in the Netherlands, however, have shown that mow- 550°C. ing and subsequent removal of the vegetation does not Between 2002 and 2004, samples from the top layer have a marked effect on J. effusus dominance in nutrient- (0–20 cm) were taken at former agricultural lands (n ¼ rich former agricultural lands in the medium term (Kemmers 61), and lands still being used for agricultural purposes et al. 2004). Most animals only feed on J. effusus after (n ¼ 49), which were expected to contain differing amounts more palatable plants have been eaten and certainly will of total calcium. For these samples, Olsen-P, total-P, and not eliminate the species (Richards & Clapham 1941; total calcium were determined as described below. Merchant 1993). Grazing may even enhance J. effusus development, as more open patches are created by tram- pling, which rapidly become colonized by J. effusus. This Experiments even tends to give this species a strong competitive advan- Experiment 1. For this experiment, a quantity of sandy tage over other species in a grazed terrain (Kemmers et al. soil was collected from a depth of 10–20 cm in an aban- 2004). Removal of the top layer, or sod cutting, frequently doned agricultural field from the Netherlands. Maize had does not prevent the establishment of J. effusus. Remov- been cultivated on the land for more than a decade and ing the vegetation may even be beneficial to the species by the soil had been heavily fertilized. The soil was collected creating space for seedlings to establish (Wetzel & Howe approximately 5 years after agricultural use had ended. 1999). The soil was homogenized and divided into three portions, However, observations have shown that on more calcar- which were provided with 0, 10, and 20 g, respectively, of eous soils, the development of J. effusus after the ter- lime (‘‘Dolokal’’: 75% CaCO3, 10% MgCO3, and 5% mination of agricultural use appears to be much less MgO) per kilogram mixed through the fresh soil. For each pronounced, and in some cases, a development has been soil type (i.e., 0, 10, and 20 g Dolokal/kg fresh soil), eight observed towards a more diverse and species-rich vege- glass containers with a diameter of 15 cm and a height of tation, without additional measures. This suggests that 20 cm were filled with 10 cm of soil. Next, a 10-cm layer of liming might inhibit the growth of J. effusus. In this article, distilled water was carefully poured on top of the soil in we present the results of field measurements/observations four of the eight containers after which the water levels in and experiments, which examined the relationship be- these containers was kept constant. In the remaining con- tween nutrient availability and J. effusus growth on former tainers, the soil was kept moist by spraying with distilled agricultural lands with noncalcareous sandy soils and the water twice a week. The containers were kept in the dark possible beneficial effects of liming. at 16°C for 90 days. After 90 days, samples of the water layer (if present) and pore water samples were taken from the containers. Methods Pore water samples were taken with the aid of soil mois- ture samplers (Rhizon SMS-10 cm; Eijkelkamp Agrisearch Field Sampling Equipment, Giesbeck, The Netherlands) by connecting the Between 2000 and 2002, soil samples were taken through- samplers to nitrogen preflushed vacuum infusion flasks. out the Netherlands at a large number of field locations At the end of the experiment, the soils were dried (24 with sandy soils, using an Edelman soil sampler. On for- hours at 70°C) and ground up. Olsen-P extracts and diges- mer agricultural lands with noncalcareous sandy soils (36 tates from the soils were prepared as described below. locations), samples were taken from the following depths: 0–20, 20–40, 40–50, 50–60, and 60–70 cm. The usage of Experiment 2. For this experiment, a quantity of sandy these former agricultural lands had been stopped between soil was collected from depths of 0–20 and 50–60 cm from

JUNE 2008 Restoration Ecology 241 Decreasing the Abundance of Juncus effusus on Former Agricultural Lands an abandoned agricultural land. Maize had been cultivated Olsen et al. (1954). Samples from the water layer were on the land for more than a decade and the soil had been filtered (0.45 lm). heavily fertilized. The soil was collected approximately 5 Alkalinity and pH of the samples were determined years after agricultural use had stopped. The soil collected immediately after collection. Alkalinity was determined from each depth was homogenized and divided into three by titrating a known volume of sample with 0.01 M HCl portions, which were provided with 0, 5, and 20 g, respec- down to pH 4.2. Ortho-phosphate was measured accord- tively, of lime (Dolokal: 75% CaCO3, 10% MgCO3, and ing to Henriksen (1965), ammonium according to Grassh- 5% MgO) per kilogram mixed through the fresh soil. For off and Johannsen (1977), and nitrate according to each soil type (topsoil with 0, 5, and 20 g lime/kg fresh soil Kamphake et al. (1967). Fe, Mn, Ca, Mg, P, and S were and deep soil with 0, 5, and 20 g lime/kg fresh soil), two analyzed using an inductively coupled plasma emission glass containers with a diameter of 15 cm and a height of spectrophotometer (Spectroflame, Spectro Inc., Littleton, 20 cm were filled with 10 cm of soil. Next, five seedlings of CO, U.S.A.). Na and K were measured using a Technicon J. effusus were carefully planted in each container. The Flame Photometer IV. containers were kept at a temperature of 18°C, and light- ing was provided with a photoperiod of 16 hours at 22 21 220 lmolm second . The soils were kept wet by adding Results distilled water every 2 days. After 3 months, pore water samples were taken from the soils with the aid of soil Field Sampling water collectors (Rhizon SMS-10 cm; Eijkelkamp Agri- The results of the field sampling showed a large difference search Equipment) by connecting the samplers to nitrogen in the availability of P between the topsoil layer of the ref- preflushed vacuum infusion flasks. The plants were then erence sites and that of the former agricultural lands harvested and both plants and soils were dried (24 hours (Table 1). As was to be expected, P concentrations in the at 70°C) and ground up. Olsen-P extracts were prepared water and salt extracts, as well as the Olsen-P (considered and digestates from the soils and shoots were prepared as an estimate of bioavailable P) and total-P concentrations, described below. were much higher on the agricultural lands. Potassium (K) 2 and nitrate (NO3 ) concentrations in the salt extracts were also much higher in the topsoils of the agricultural lands. Analysis Figure 1 reveals a significant relationship (power func- Total-P and total-Ca concentrations were determined in tion) between the total-Ca concentration and the ratio digestates of dried, ground-up soil. Digestates were pre- between Olsen-P and total-P (Olsen-P:total-P) for the top- pared by combusting soil samples in nitric acid and hydro- soil layers we sampled. The Olsen-P:total-P ratio was low gen peroxide for 16 minutes with the aid of a Milestone at high total-Ca concentrations but increased considerably microwave (type mls 1200 Mega). After dilution with at total-Ca concentrations less than 40 lmolkg21dry demineralized water, the digestates were kept at 220°C weight (DW). There was a difference between abandoned until analysis (see below). Water extracts (1:2 [w/v]) and agricultural lands (>5 years without agricultural practice) NaCl extracts (0.2 mol NaCl; 1:2 [w/v]) were prepared by and lands still used for agricultural purposes. In aban- shaking the soil suspension for 1 hour after which the sus- doned agricultural lands, the Olsen-P:total-P ratio was pensions were centrifuged and the supernatants filtered very low (<0.01) at high total-Ca concentrations, whereas (0.45 lm). Olsen-P extracts were prepared according to in agricultural lands that were still in use, the Olsen-P:total-P

Table 1. Chemical characteristics of the top layer of former agricultural soils with noncalcareous sandy soils and soils under reference vegetations (moist nutrient-poor grasslands and mostly wet heathlands) from the Netherlands.*

Reference Agricultural Lands n 35 36 P (water) (lmolkg21DW) 0.5 (0.1–1.5) 90 (19.5–236) P (NaCl) (lmolkg21DW) 8.2 (1.8–22.5) 132 (2.2–336) Total-P (mmolkg21DW) 1.67 (0.62–3.17) 17.87 (5.89–36.50) Olsen-P (lmolkg21DW) 164 (34–320) 2,806 (693–5,608) K (NaCl) (lmolkg21DW) 281 (87–519) 2,027 (210–5,370) 1 21 NH4 (NaCl) lmolkg DW) 143 (22–500) 181 (43–383) 2 21 NO3 (water) (lmolkg DW) 17.6 (0.5–71.9) 477 (5.0–1,728) pH (NaCl) 4.2 (3.3–6.1) 5.4 (4.6–6.5) Organic matter (%) 3.3 (0.4–7.1) 4.5 (2.8–7.1)

*Data are given as mean values, with 0.05 and 0.95 percentiles in parentheses.

242 Restoration Ecology JUNE 2008 Decreasing the Abundance of Juncus effusus on Former Agricultural Lands

A. Abandoned agricultural lands B. Agricultural lands ) ) -1 -1 0.6 0.6

0.5 0.5

0.4 0.4

0.3 0.3

0.2 y = 5.1054x-1.3275 0.2 y = 0.3606x-0.3454 2 2 0.1 R = 0.7855 0.1 R = 0.3415

0 0 Olsen-P:Total-P (µmol µmol Olsen-P:Total-P (µmol µmol 0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800 Total-Ca (mmol kg-1 DW) Total-Ca (mmol kg-1 DW)

Figure 1. Relationship between the Olsen-P:total-P ratio (lmol/lmol) and the total-Ca concentration (mmolkg21DW) in the top layer of agricultural lands still in use (n ¼ 49) and abandoned agricultural lands (n ¼ 61). ratio did not become much lower than 0.1 at high total-Ca soil, based on the total-P values measured at our reference concentrations. sites), and assuming that 10 kgha21a21 (a very optimistic On one former agricultural field (examined 2 years after value) can be removed from the upper 25 cm of the soil. It the topsoil had been removed), soil samples were col- is clear that it may take at least decades and, in many lected from 13 subplots, and Juncus effusus biomass was cases, more than a century before P becomes limiting. determined. The results revealed a significant linear corre- Mowing mainly appears to be beneficial when P availabil- lation between the J. effusus biomass and the Olsen-P ity is already very near the required values or to maintain concentration in the soil (Fig. 2). Very low Olsen-P biodiverse seminatural vegetation types. concentrations were associated with low J. effusus bio- mass, whereas Olsen-P concentrations higher than approxi- 21 mately 250 lmol kg DW were consistently associated Experiment 1 with J. effusus biomass of over 750 g DW m22. No correla- The results (Fig. 4) show that liming can greatly decrease tions were found between the biomass and the availability P concentrations in soil pore water. Olsen-P concentra- of N (NH 1,NO2) and K, or with acidity-related param- 4 3 tions were also lower in the limed soils. The larger the eters (Ca, HCO 2, pH) (data not shown). 3 amount of lime added, the lower the Olsen-P concentra- Figure 3 shows the total-P concentrations at the differ- tion in the soil. No differences were observed between the ent soil depths in the agricultural land samples, as well as submerged and the moist treatments. Pore water calcium total-P concentrations measured in the top layers at the concentrations, pore water alkalinity, and pH increased as various reference sites. Figure 3 also indicates the time span a result of liming as was to be expected. needed to achieve P-limited conditions (2,500 lmol kg21

45000 5000 40000 ) -2 4000 35000 y = 4.7705x - 528

R2 = 0.9093 DW) 30000 -1 3000 25000

20000 200 years 2000 biomass (g DW m 15000 125 years

1000 Total-P (µmol kg 10000 75 years

J. effusus 5000 25 years 0 0 0 250 500 750 1000 0-20 20-4023 40-50 50-60 4560-70 R Olsen-P (µmol kg-1 DW) Figure 3. Total-P concentrations at different soil depths in agricul- Figure 2. Relationship between Juncus effusus biomass and Olsen-P tural lands with noncalcareous sandy soils (n ¼ 36). X-axis indicates concentration in subplots of an abandoned agricultural field with soils depth in centimeter. R represents the topsoil (0–20 cm) at a noncalcareous soil whose topsoil (20–40 cm) had been removed reference sites with species-rich heathlands and grasslands. 2 years earlier. Each point represents a different location (n ¼ 35).

JUNE 2008 Restoration Ecology 243 Decreasing the Abundance of Juncus effusus on Former Agricultural Lands

P-pore water (µmol L-1) P-Olsen (µmol kg-1 DW) Ca-pore water (µmol L-1 ) 120 5000 2000

100 4000 1500 80 3000 60 1000 2000 40 500 20 1000 0 0 0 subm moist subm moist subm moist subm moist subm moist subm moist subm moist subm moist subm moist

01020 01020 01020

Fe-pore water (µmol L-1) Fe:PO4 pore water (µmol µmol-1) pH-pore water 40 2.0 8

30 1.5 7 20 1.0 6 10 0.5

0 0.0 5 subm moist subm moist subm moist subm moist subm moist subm moist subm moist subm moist subm moist

01020 01020 01020

Figure 4. Parameters of submerged and moist noncalcareous sandy soils provided with 0, 10, or 20 g of Dolokal/kg fresh soil (experiment 1; see Methods). Horizontal bars indicate standard error (N ¼ 4).

Pore water iron concentrations were much higher in the We never found similar relationships between J. effusus submerged soil than in the moist treatments. In combina- growth and ammonium, nitrate, potassium, calcium, alka- tion with the decreased pore water P concentrations, this linity, or pH. Apparently, under the given circumstances resulted in greatly increased Fe:P ratios in the pore water of in the Netherlands, with high nitrogen deposition levels the submerged and limed soils. Pore water iron concentra- (Bobbink et al. 1998), nitrogen is not likely to limit the tions were lower in the limed soils than in the unlimed soils. growth of J. effusus. It can be concluded that it is hard to avoid colonization by J. effusus on wet soils, as the species is able to thrive even at relatively low Olsen-P concentra- Experiment 2 tions. Over a threshold of 200–300 lmol/kg soil, however, Figure 5 shows the results of the experiment. P concentra- it becomes increasingly dominant. tions and organic matter content were generally much P availability is known to be limited on calcareous lower in the deeper soil layer than in the top layer. Addi- soils because of precipitation of dicalcium phosphate tion of lime decreased the Olsen-P concentrations in the (CaHPO4) and sorption of P to calcite (Samadi & Gilkes top layer, but they remained high. P concentrations in the 1999; Tunesi et al. 1999; Curtin & Syers 2001; Berg et al. pore water were greatly affected by lime additions. Juncus 2004). Our field survey showed that P availability (ex- effusus biomass and the P content of J. effusus shoots at pressed as the Olsen-P:total-P ratio) is strongly influenced the end of the experiment, however, were not affected by lime by the total-Ca concentration of the soil. P availability addition. P contents were much lower in the deeper soil layer appears to increase strongly at total-Ca concentrations than in the top layer, which resulted in a much lower J. effusus below 40 mmolkg21DW. Most overfertilized agricultural biomass on the deeper soil compared with the topsoil. soils in the Netherlands fall within this category. In soils with a much higher Ca concentration, P availability can become very low, especially in abandoned agricultural Discussion lands. P availability in agricultural land that is still being Our results reveal that the growth of Juncus effusus on fertilized remains somewhat higher than in abandoned moist or wet soils seems to be largely determined by the soils. This is consistent with the view that, in the course of Olsen-P concentration in the soil. Olsen-P can be time, more insoluble Ca–P phases are formed (Steefel & regarded as a relevant and easily measurable value for Van Cappellen 1990; Scheffer & Schachtschabel 1992). plant-available P (Olsen et al. 1954). In our experiments Our liming experiments allow the conclusion that P and field measurements, we found a clear relationship concentrations in soil pore water in noncalcareous sandy between J. effusus growth and Olsen-P concentrations. soils in the Netherlands can be greatly decreased by

244 Restoration Ecology JUNE 2008 Decreasing the Abundance of Juncus effusus on Former Agricultural Lands

Olsen-P (µmol kg-1 DW) Biomass (g DW) P-shoot (µmol g-1 DW) 5000 1.0 300 4000 0.8 250 200 3000 0.6 150 2000 0.4 100 1000 0.2 50 0 0.0 0 0 0 5 5 0 0 5 5 0 0 5 5 0 0 5 5 0 0 5 5 0 0 5 5 20 20 20 20 20 20 20 20 20 20 20 20 Top Deep Top Deep Top Deep

Tot P-soil (mmol kg-1 DW) P-pore water (µmol L-1) Org. Mat.-soil (% DW) 25 20 5

20 15 4 15 3 10 10 2 5 5 1 0 0 0 0 0 5 5 0 0 5 5 0 0 5 5 0 0 5 5 0 0 5 5 0 0 5 5 20 20 20 20 20 20 20 20 20 20 20 20 Top Deep Top Deep Top Deep

tot Ca-soil (mmol kg-1) Ca-pore water (µmol L-1) pH-pore water 300 4000 8 250 3000 7 200 150 2000 6 100 1000 5 50 0 0 4 0 0 5 5 0 0 5 5 0 0 5 5 0 0 5 5 0 0 5 5 0 0 5 5 20 20 20 20 20 20 20 20 20 20 20 20 Top Deep Top Deep Top Deep

Figure 5. Parameters of submerged and moist noncalcareous sandy soils and the Juncus effusus plants growing on these soils (experiment 2; see Methods), which were provided with 0, 5, or 20 g of Dolokal/kg fresh soil. Two different soils samples were used, one from the topsoil (0–20 cm; left part) and one from a deeper soil layer (50–60 cm; right part) at an agricultural field. The experiment was carried out in duplicate. liming. However, liming soils with high total-P concentra- It can be concluded that the restoration of a diverse and tions very slightly decreased Olsen-P concentrations and species-rich vegetation on agricultural lands with a noncal- did not affect the growth of J. effusus. This is true at least careous sandy soil will in most cases not be possible within on the short term. Experiments on the long term should a reasonable time span without removal of the topsoil. provide information on the possible formation of more Although this is almost always a relatively expensive meas- insoluble Ca–P phases in the course of time as suggested ure, it may be cheaper in the long term than keeping up by Steefel and Van Cappellen (1990). a mowing regime for decades. Experiences with topsoil Mining soil phosphate (by harvesting crops that have removal in the Netherlands have been positive (Lamers taken up P from the soil, often with N- and K fertilization et al. 2005). In cases where the P concentrations in the soil to increase the harvest, and followed by removal of the profile were determined and where enough soil was biomass from the site) can be a valuable measure to de- removed to create P limitation, problems with luxurious crease the P availability in soils (Koopmans et al. 2004a, J. effusus growth were limited to small parts of the area. It 2004b). This can especially be used to considerably reduce is important, however, to study P concentrations at various P concentrations in pore water, thus diminishing the risk depths to establish the amount of soil that has to be of P leaching from agricultural lands (Koopmans et al. removed. In many cases, heavy fertilization will have led to 2004a, 2004c). Based on experiments, Koopmans et al. P leaching to deeper soil layers, and in some cases, the con- (2004a) calculated that in the long term, 65% of the clusion might be that, even after soil removal, a species-rich adsorbed P could be removed by plant mining. It can be (nutrient-limited) vegetation is not a realistic objective. concluded that even after prolonged P mining, its avail- A drawback of topsoil removal might be that the seed ability would probably remain far too high to prevent lux- bank is destroyed (Grootjans et al. 2001). On most former urious growth of J. effusus on former agricultural lands. In agricultural lands, however, the recruitment potential for addition, biomass production and P mining will slow down the target species from the seed bank is very poor anyway at decreasing P availability. because many rare herbaceous species do not form

JUNE 2008 Restoration Ecology 245 Decreasing the Abundance of Juncus effusus on Former Agricultural Lands

under drained conditions and to the water layer under submerged conditions. The latter is important as rewetting of agricultural lands frequently results in partly inundated conditions and because former agricultural lands are being considered for use as permanent or temporary water stor- age facilities. Inundation results in anaerobic conditions in the soil and hence in the reduction of iron(hydr)oxides. As a result, iron and iron-bound phosphate become mobi- lized (Patrick & Khalid 1974; Wetzel 2001; Lamers et al. 2002; Lucassen et al. 2004) (Fig. 6). This is illustrated by the results of experiment 2, which show that the submerged soils had higher Fe and P con- centrations in the pore water than the control soils. Lim- ingalsodecreasedtheironconcentrationinporewater under submerged conditions, probably as a result of iron carbonate precipitation (Drever 1997). However, the Fe:P ratio in the pore water largely determines the Figure 6. Dominance of J. effusus and filamentous algae on an exchange of P with the water layer (Smolders et al. abandoned and rewetted agricultural land in The Netherlands 2001). As liming considerably increases the Fe:P ratios, it (Photo by Esther Lucassen). will decrease the exchange of phosphate with the water layer. a persistent seed bank (Bekker et al. 1996, 2000). As a result, it is especially the undesirable species with more persistent seeds, such as J. effusus, that tend to dominate Implications for Practice the seed bank. Hence, the establishment of the target spe- d If removal of the topsoil is considered to create P cies depends on the presence of remaining nearby popula- limitation, it is important to study P concentrations tions and their dispersal capacity (Bekker et al. 2000; at various depths to establish the amount of soil that Grootjans et al. 2001; Ozinga et al. 2005). Although in has to be removed. some cases a highly diverse vegetation has developed even d Liming of noncalcareous soils may create better soil without species being reintroduced (Tallowin & Smith properties for the establishment of the desired spe- 2001; Lucassen & Roelofs 2005), in many cases, additional cies as it may prevent acidification and pH-related measures such as the reintroduction of species will deserve toxicity. serious consideration (Patzelt et al. 2001; Pywell et al. d When former agricultural land becomes (temporar- 2002; Van den Berg et al. 2003; Vergeer 2005). ily) inundated after topsoil removal, liming might be Experiment 2 confirms that removing the top layer, a good measure to prevent the luxurious growth of resulting in much lower Olsen-P levels in the soil, has algae in the water layer by decreasing the sediment a much greater effect on the growth of J. effusus than lim- pore water P concentrations and hence the release of ing, at least on the middle term. This means that liming of P to the overlying water layer. agricultural soils does not seem to be an alternative to top- d Historically, the nutrient-deficient heathlands and bi- soil removal to decrease the growth of J. effusus. Never- odiverse grasslands on sandy soils in the Netherlands theless, liming might be a valuable additional measure to have been turned into either agricultural lands or enhance the quality of the soil after topsoil removal. pine forest plantations. The pine forest plantations Noncalcareous agricultural soils, for instance, are limed have never been fertilized, which means that redevel- to prevent acidification of the top layer because of nitrifi- opment of wet and dry heathland, after removal of cation of ammonium. In the deeper soil layers, however, the trees and litter, is easily achievable. A win–win calcium is leached, resulting in very low total-Ca concen- situation can be created by establishing fast grow- trations. As a result, these noncalcareous mineral soils can ing new forest plantations on former agricultural become very susceptible to acidification after topsoil land and recreating heathlands and biodiverse grass- removal. Liming might then be beneficial to prevent acidi- lands on land dominated by low-quality pine forest fication and further enhance P immobilization in the plantations. soils. The germination and establishment of the target spe- cies might be greatly stimulated by additional liming, as this will prevent ammonium and aluminum toxicity (De Graaf et al. 1998; Lucassen et al. 2002; Van den Berg Acknowledgments et al. 2003). The authors wish to thank Mr. Jelle Eygensteyn for his Next, decreased P concentrations in soil pore water can assistance with the analyses and Mr. Jan Klerkx for greatly reduce the risk of P leaching to the groundwater improving the English.

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