Alain Peeters

Relationship between soil chemical factors and grassland diversity

Many studies carried out during these last few years have focused on the factors influencing plant diversity in species-rich grasslands. This is due to the fact that these ecosystems, among the most diversified in temperate climates, are extremely threatened; in some areas, they have almost disappeared. The re-establishment of these habitats implies to know the living conditions of the associations to be recreated. Very often, the typical species of these communities have become so rarefied that the seed bank or the seed rain are not sufficient to recreate the plant community. Most of the time, to achieve the restoration of these communities, they have to be totally recreated by sowing. For the restoration or the maintenance of the community, the soil chemical characteristics have also to be appropriate or if not modified. This research tends to establish a relation between some soil chemical factors and the plant diversity of a great number of stations. This research has illuminated the relationship between soil extractable phosphorus and potassium and plant diversity. Over 5 mg of phosphorus per 100 g of dry soil (acetate + EDTA extraction), no station containing more than 20 species per 100 m2 has been found. The highest number of species is found below the optimum content of the soil for plant nutrition (5–8 mg P/100 g). Concerning the potassium, the highest number of species is found at 20 mg/100, a value corresponcing to an optimum content of the soil for plant nutrition. High potassium contents, in opposition to phosphorus contents, are thus compatible with high values of diversity. Other factors (i.e. pH, organic matter, total nitrogen and calcium) do not show so clearly a relation with plant diversity. Excess of N–NO3 is known for its negative effect on the diversity of plant communities. In these environments, apart from the atmospheric deposits which can be important in some areas, N–NO3 is derived mainly from the symbiotic fixation of atmospheric nitrogen by legumes as well as from the mineralization of the organic matter of the soil. It is possible that, when in small quantities, the available soil phosphorus could be a limiting factor of the N–NO3 supply by these two sources. In this hypothesis, nitrogen would remain the main element limitating plant diversity but its availability would be controlled by phosphorus.

Phosphorus removal by a synthetic iron oxide–gypsum compound

Phosphorus pollution is a major concern for soil and water management. This study assesses the phosphate and organic phosphorus removal capacity of an iron oxide-gypsum compound (named OX) in batch trials. Phosphate solutions ranging from 0.001 to 10 mg P l(-1) were tested and OX proved to be an effective fixing agent. Solutions with different ionic strengths did not affect this reactivity. Phosphate removal was not altered by pH values between 4 and 8, but increased significantly with higher values. Near-completion of this reaction was observed after some minutes. The combined effects of precipitation with calcium (gypsum) and sorption onto the oxide explain these interesting properties. The phosphate removal capacity was demonstrated on field samples. The compound also promoted the hydrolysis of a model organic phosphorus molecule. Contact of OX with solutions with pH values between 4 and 10 did not alter its stability but caused pH levelling to neutral values. Other secondary effects involve sulfate and calcium release. OX reactivity with different phosphorus species under various conditions is interesting for application to water and soil remediation processes aiming to control phosphorus pollution

Reintroduction of Nassella pulchra to California coastal grasslands: Effects of topsoil removal, plant neighbour removal and grazing

ABSTRACT Question: What is the most appropriate combination of treatments to reintroduce Nassella pulchra, a perennial bunchgrass, into degraded mediterranean coastal grasslands? Location: Central coast of California, USA. Methods: N. pulchra was sown from seeds and transplanted into a degraded grassland in a multi-factorial experiment testing the effects of (1) two grazing intensities (lightly grazed by native mammal species or ungrazed); (2) topsoil removal and (3) reduction of plant neighbours. The experiment was carried out on two types of surrounding vegetation (exotic annual grasses and exotic forbs). Results: Topsoil removal greatly enhanced establishment from seeds and transplant survival, mainly because it reduced the exotic vegetation and thus reduced competition. While removing neighbours was essential when topsoil was left intact, it had a negative effect on N. pulchra when surrounding species included exotic forbs (Brassica spec. and Asteraceae) at low density (after topsoil removal). Moderate grazing by native mammals (deer, rabbits and gophers) did not affect N. pulchra. Conclusion: Our results suggest that seeding after topsoil has been removed is a promising method to reintroduce N. pulchra to highly degraded sites where there is little to no native seed bank. Nomenclature: Hickman 1993.

LAI evolution of a perennial ryegrass crop estimated from the sum of temperatures in spring time

When there is sufficient fertiliser, the development of the canopy (LAI less than or equal to 4) of a perennial ryegrass crop during regrowth after winter or after a cut in spring time, essentially depends on the temperature. The expression of the Leaf Area Index (LAI) according to the sum of average positive temperatures instead of relatively to the number of days highly improves the relationship. This is verified at three sites, where climatic conditions are different, during 2 consecutive years and is written L = 0.0193 Sigma T-0.3107 (Tin degrees C). On average, 52 degrees C/day are required to allow a LAI increase of 1 unit in spring time. The LAI expansion results from the increase of the number of tillers, of leaves per tiller and of the leaf area. The relationship between the sum of temperatures and each of these factors is not significant, except for the tiller density. Adversely, the result obtained by the product of these factors, the LAI, is significantly correlated to the sum of average positive temperatures calculated from the beginning of the growth after winter

Nutritive value of some tropical grasses used by traditional small farms in the highlands of Burundi

The objective was to estimate—according to the French feeding system—the nutritive value of three tropical grasses (Eragrostis olivacea, Setaria sphacelata and Tripsacum laxum) used in traditional small farms of Burundi. Dry matter (DM) yield was monitored on anti-erosive hedges or on small fields in 60 small farms for eight consecutive years. DM intake and digestibility values were measured on seven steers or seven male sheep. Degradability values were determined on three sheep. S. sphacelata exhibited higher DM yield (t ha−1), energy (UF, kg−1 DM) and protein (PDI, g kg−1 DM) values (17.3, 0.73 and 68, respectively) than T. laxum (9.11, 0.64 and 47) and E. olivacea (not determined, 0.46 and 42). The UF and PDI intakes of these grass species were able to meet only 51% to 92% of the energy and 59% to 133% of the protein requirements for maintenance of the experimental animals.