Aboveground Phytomass Production Research Articles

Productivity of grassland ecosystems in the Tyva Republic, Russia

The aim of the study. The aim of the study was to estimate biological productivity of Tyva grasslands. Location and time of the study. The living and dead above- and belowground phytomass, as well as net primary production, were estimated in the montane ecosystems and depressions of the Tyva Republic, Russia. Methodology. Field and laboratory studies of the biological production by grasslands were conducted using botanical, geobotanical and ecological methods. Main results. In the montane ecosystems the aboveground phytomass production was shown to range from 1.3 to 3.6 Mg ha-1 yr-1, whereas the belowground production was evaluated as ranging 10-65 Mg ha-1 yr-1. The belowground production was found to vary widely, being associated with location of mountain ridges, slope geomorphology and grazing, but no association was found with the altitude. In depressions the average green phytomass stock changed from 0.7 to 1.9 Mg ha-1, living belowground phytomass varied 3.4 to 19.3 Mg ha-1. From the meadow steppes to the deserted ones the living above- and belowground stocks decreased 2.7 and 5.7 fold, respectively, whereas the above- and belowground production was estimated to decrease 3 and 4 times, respectively. Several indices to characterize the growth and development, hence the productivity, of herbaceous plants was proposed. The values of the indices calculated for the Tyva grasslands suggested high photosynthetic activity: all studied steppes had the same share of belowground production in the total ecosystem production, i.e. 90%. The turnover rate of the living belowground phytomass was estimated to increase from meadow steppes to the deserted ones, whereas green phytomass increment, as related to its stock, slightly decreased. Conclusions. The living belowground phytomass stock was found to exceed the green phytomass stock by 5-8 times, both in montane ecosystems and depressions. Preservation of living belowground organs during hot dry summers and cold winters, when soil freezes through, is apparently indispensable for grassland survival under any climatic conditions.

Plant traits and phenotypic variability effect on the phytomass production ofStipagrostis ciliata (Desf.) De Winter.

A process of continuous degradation of plant communities, due mainly to long-term overgrazing has been revealed by most ecological studies in North African arid climate. Notably, this degradation appeared across the depletion of perennial grass species exhibiting low density in the majority of range ecosystems. This study aimed to examine the phenology and the aboveground phytomass production of Stipagrostis ciliata (Desf.) De Winter accessions, a perennial grass, growing under the same environment but coming from different climates of Tunisia. Additionally, the extent of genetic variation in phenological parameters, root and shoot phytomass productivity and the correlations among these parameters were also analyzed. Significant differences in all morphological parameters of S. ciliata accessions were revealed by ANOVA test and were corroborated with significant and positive correlation indicated by Pearson’s correlation analysis. Plant diameter, biovolume, root biomass with protective sleeve and spike number exhibited significant differences and high distinctiveness between S. ciliata accessions. Tukey’s HDS tests indicated the presence of three groups of accessions. Principal component analysis (PCA) applied on a table with eight observations and 13 variables, and dispersion of S. ciliata accessions on the first two axes of PCA confirmed the presence of three groups of accessions. Trait variability in the field for the five accessions is more likely to be the result of phenotypic plasticity rather than of genetic differentiation between accessions. Overall, the characterization of S. ciliata accessions exhibited significant differences in terms of morphological and biomass productivity.

Short communication: Effects of summer rainfall variations on sheep body state and farming sustainability in sub-Mediterranean pastoral systems

In sub-Mediterranean climate the grassland aboveground phytomass production peaks in late spring and drops in summer, when the decrease of the pasture feed value may lead to the worsening of the animal welfare. Our goal was to define the summer rainfall values leading to a decrease of semi-extensive farming system sustainability in sub-Mediterranean regions. Summer rainfall variations reflect in the aboveground phytomass production and on the sheep body state. Differences of body condition score (BCS) among years were significant in late summer, which is the mating period for sheep. In the driest year the BCS of end August drops down to 2.1, largely below the value considered sufficient to ensure the animal breeding/milking performances (2.5). Reduction of summer rainfall greater than 15–20% compared to the normal average value (thus less than expected by the scenario of climate change) might be detrimental for semi-extensive rearing sustainability in sub-Mediterranean climate.

Луговая растительность пойм рек Вычегда и Печора. Порядок Arrhenatheretalia R. Tx. 1931

The present study continues a series of publications of the authors on diversity of the meadow vegetation in the floodplains of the Vychegda and Pechora rivers and their tributaries (Komi Republic). The floristic classification of wet meadows of the order Molinietalia Koch 1926 was published early (Shushpanikova, Yamalov, 2013). The results of floristic classification of meadow vegetation belonging to the order Arrhenatheretalia R. Tx. 1937 are discussed in this article. Analysis was based on 383 original relevés of the meadow vegetation of the order Arrhenatheretalia made in accordance with principles of the Braun-Blanquet approach (Braun-Blanquet, 1964; Mirkin and Naumova, 1998). The studies were performed in the floodplains of the Vychegda and Pechora rivers and their tributaries (Sysola, Kazhym, Pozheg, Viled, Usa, Colva, Synya, Sebys, Ilych, Syuzyu, Shchugor). The descriptions were conducted at the study plots of 10×10 m. Plant communities of small size were described within the natural limits. A location, dimensions of community, species composition, species saturation, composition of dominant and co-dominant species, total coverage and height of grass stand, aboveground phytomass production were identified. The abundance of species in meadow communities was recorded using the J. Braun-Blanquet method: r — species occurs sporadically, + — minor species, total coverage less than 1 %, 1 — 1–5 %, 2 — 6–25 % 3 — 26–50 %, 4 — 51–75 %, 5 — 76–100 %. The assessment of environmental parameters was performed by ecological methods of L. G. Ramensky (Ramensky et al., 1956). Syntaxonomic diversity of the meadow vegetation of the order Arrhenatheretalia of the Vychegda and Pechora rivers floodplains presented by 2 unions (Cynosurion R. Tx. 1947 и Festucion pratensis Sipaylova et al. 1985), 7 associations (Festucetum ovinae Turubanova 1986, Festuco pratensis–Deschampsietum caespitosae Turubanova 1986, Anthoxantho odorati–Agrostietum tenuis Sillinger 1933, Festuceto pratensis–Dactyletum glomeratae Dymina 1989 in Korolyuk et Kiprijanova 1998, Amorio repens–Poetum pratensis ass. nov., Equiseto arvensis–Elytrigietum repentis Maraculina 2009, Elytrigio repentis–Bromopsidetum inermis Yamalov 2011. Two new communities without rank are described (Agrostis vinealis, Hypericum maculatum–Phleum pratense). Most plant associations are heterogeneous by their floristic composition and they can be divided into 10 subassociations and 5 variants. The peculiarities of the floristic composition of the above mentioned associations, as well as their distribution and ecology are discussed. The distinguished associations are well differentiated by their elevation level on the floodplains. The meadow communities of Festucetum ovinae are located on the highest floodplains in the inland zone; there is Agrostis vinealis in the streamside zone of the floodplains. The meadow communities of the ass. Anthoxantho odorati–Agrostietum tenuis are located on the low floodplains in the streamside zone. The meadow communities of the associations Festuco pratensis–Deschampsietum caespitosae, Equiseto arvensis–Elytrigietum repentis, Elytrigio repentis–Bromopsidetum inermis, Festuceto pratensis–Dactyletum glomeratae are occupied the medium level floodplains. The meadow communities of the ass. Amorio repens–Poetum pratensis are found at different locations of the floodplain; they are formed under grazing. The described meadows grow on the soils with different ecological indicators. The distinguished associations are differentiated by water level (52.2–73.0), average figures — 55.9–68.9. The meadow communities of the ass. Festucetum ovinae occupy the driest sites of the floodplain; the ass. Anthoxantho odorati–Agrostietum tenuis is located in the wettest floodplains. The meadow communities of the ass. Elytrigio repentis–Bromopsidetum inermis occupy most rich and alluvial soils. They are located on the low ridges in the middle zone of the floodplain and they are formed by annual flooding on alluvial deposits. The distinguished associations are differentiated by pH (4.2–8.0), average figures — 4.9–7.0. The meadow communities with Agrostis vinealis are occupied the most acidic soil. The meadow communities of the ass. Anthoxantho odorati–Agrostietum tenuis are located on the neutral soils. The meadow communities of the most of associations occupy slightly acidic soils. The variability of moisture varies from alternating values to high values. The greatest differences in moisture are demonstrated by the communities of associations Equiseto arvensis–Elytrigietum repentis and Elytrigio repentis–Bromopsidetum inermis located on middle manes on low and medium levels of the floodplains. The associations are differ by the scale of pasture digression in range 3.3–5.0, average figures — 3.8–4.9. The meadow communities with Agrostis vinealis have the highest rates of pasture digression (4.5–5.1). The meadow communities of the ass. Anthoxantho odorati–Agrostietum tenuis have the smallest ones (3.5–3.9). A comparison of species composition of the syntaxa in Komi Republic with communities described in other regions of the Eastern Europe and the Asian part of Russia was carried out. It was shown that the meadow communities of the Komi Republic have low species diversity. Species richness of meadow communities is less than 39 species on trial area. The meadow communities of the ass. Festuco pratensis–Deschampsietum caespitosae are the richest. 195 vascular plant species are recorded in 213 geobotanical descriptions of the order Arrhenatheretalia. The aboveground phytomass varies from 20–40 g/m2 (Festucetum ovinae) to 520 g/m2 (Festuco pratensis–Deschampsietum caespitosae).

The turfs quality of selected Slovak varieties of the genus Festuca under the conditions without irrigation

The development of botanical composition (in % dominance) in the period 2005–2011 and growth-production process in the years 2007–2011 were evaluated in small-plots experiment with selected Slovak varieties of species of the genus Festuca. The experiment was realized under the conditions without irrigation of south-western Slovakia (locality Nitra). The data of botanical composition of turfs showed that fescue varieties were able to create well-covered vegetation (coverage 87–99 %) as early as next year after sowing in conditions without irrigation. In the next period, the differences in turf coverage between varieties were minimized. The total height of turf and average daily gain of height were the highest in F. arundinacea Schreb. varieties throughout the observed period with significant differences in year 2008 (p = 0.0239), 2009 (p = 0.0462) and 2011 (p = 0.0036). The most intensive growth had F. arundinacea Schreb. cv. Koreta (1.81 to 3.44 mm.d−1; i.e. very low to moderate intensity of growth). From point of view of aboveground phytomass production almost throughout the period were used varieties characterized by very low production of phytomass. Among years and varieties were observed differences in the ability thicken vegetation expressed as the ratio of the average daily gain of weight and average daily gain of height (W/H). F. rubra L. cv. Laroma (0.38 to 1.26 g.m−2.mm−1) and F. ovina L. cv. Grasina (0.37 to 1.54 g.m−2.mm−1) dominated in this indicator except for 2009, when higher values reached F. arundinacea Schreb. cv. Koreta and Levona (both 0.43 g.m−2.mm−1; F. rubra L. and F. ovina L. – 0.27 and 0.39 g.m−2.mm−1, respectively).

Habitat preferences of the encroacher shrub, Seriphium plumosum

The ecology of Seriphium plumosum is not yet fully understood and therefore requires in-depth research to assist with the control of this encroacher plant. The habitat preferences of the plant were quantified for terrain morphological units in terms of soil fertility, saline/sodic conditions and soil–water relationships. The influence of S. plumosum density on grass production was also quantified. It is clear that the distribution (both occurrence and density) of S. plumosum is associated with soil characteristics. The study indicated the sensitivity of S. plumosum towards wet conditions, perennial and transient water tables, overly high soil pH, clay content, high soil fertility (organic matter and phosphate) and sodium chloride. The deeper the soil profile, the more favourable the habitat for S. plumosum, owing to a decrease in waterlogged conditions. The habitat prevalence of S. plumosum is possibly a reflection of not only climatologically wetness but also of topographic wetness. There was no clear general trend for the individual cations along the terrain units. A significant relationship was established between aboveground phytomass production loss of the grass sward and S. plumosum density. These results confirm the threat posted by S. plumosum in semiarid grassland areas, following changes in environmental characteristics.

Short-term response of the encroacher shrub Seriphium plumosum to fire

Quantification of the short-term impact of burning in terms of the encroacher shrub Seriphium plumosum and grass tuft mortality, seed germination of the shrub (field and seed bank), aboveground phytomass production, plant density and basal cover of the grass sward was conducted in semiarid grassland following an accidental fire. These variables were determined along a terrain morphological unit where S. plumosum density increased with altitude. On average 57% of S. plumosum seedlings were killed by fire, but fire had no significant (P > 0.05) influence on the mortality of mature shrubs. Fire significantly (P ≤ 0.01) stimulated seedling emergence of S. plumosum, to such an extent that an average of 510 seedlings ha−1 occurred on the foot slope, while only 9.14 seedlings ha−1 emerged in the unburnt treatment. Seedling emergence showed greater association with protection from direct sunlight and seedlings emerged not closer than 281 mm from the nearest leaves (canopy) of a mature S. plumosum shrub. The aboveground phytomass production of the unburnt grass sward was nearly double that of the burnt areas over the first season following the fire. Fire as a control measure should be carefully handled because it can lead to increased encroachment of S. plumosum.

Root studies on grass species in a semi-arid South Africa along a degradation gradient

Understanding changes in hydrological characteristics of rangeland ecosystems with degradation is essential when making rangeland management decisions in arid and semi-arid areas to ensure sustainable animal production. The impact of rangeland degradation on root production, root/shoot ratio and water-use efficiency was therefore determined for a semi-arid rangeland, over a 7-year period (1999/00 to 2005/06 growing seasons). Water-use efficiency (WUE) is defined as the quantity of above- and/or belowground phytomass produced over a certain period of time per unit of water evapotranspired. Sampling was from rangeland artificially maintained in three different rangeland conditions, viz. good, moderate and poor. As much as 86, 89 and 94% of the roots for rangelands in good, moderate and poor conditions, respectively, occurred at a depth of less than 300 mm. Root mass was strongly seasonal with the most active growth taking place during March and April. Root mass appears to be greater than aboveground phytomass for this semi-arid area, with an increase in roots in relation to aboveground phytomass production with rangeland degradation. The mean monthly root/shoot ratios for rangelands in good, moderate and poor conditions were 1.16, 1.11 and 1.37, respectively. Rangeland degradation significantly lowered above- and belowground phytomass production as well as the water-use efficiency. The mean WUE (root production included) were 4.79, 3.54 and 2.47 kg ha −1 mm −1 for rangelands in good, moderate and poor conditions, respectively. These water-use efficiency observations are among the few also including root production in its calculation. As a proportion of annual phytomass, litter fall of 7.17, 4.64 and 3.41% was obtained for rangelands in good, moderate and poor conditions, respectively. Increasing rangeland degradation increased the replacement of total root system by about 10 months and decomposition time of litter by 6 months. The importance of a well-established root system for sustainable production in the semi-arid rangelands cannot be overemphasized.

The humidity buffer capacity of clay–sand plaster filled with phytomass from treatment wetlands

The aim of our study was to measure the amount of moisture absorption and desorption in clay–sand plaster mixed with “fibre-wool” from Typha spadixes and chips of Typha and Phragmites. Common cattail ( Typha latifolia) and common reed ( Phragmites australis) are the most common plants in constructed and semi-natural wetlands for wastewater treatment, as they are highly valued in ecologically oriented construction. The cattail and reed for the experiment were harvested in a wastewater treatment subsurface flow semi-natural wetland and in two free water surface constructed wetlands which showed reliable aboveground phytomass production over a 5 years period (for Typha, 0.37–1.76 kg DW m −2 in autumn and 0.33–1.38 kg DW m −2, and for Phragmites, 0.61–1.32 and 0.61–1.02 kg DW m −2, respectively). The quantity of moisture absorption and desorption was measured in a climatic chamber where the humidity of ambient air was suddenly raised from 50% to 80% (absorption) and reduced from 80% to 50% (desorption). Over 12 h, all of the samples released the same amount of water as they absorbed. The clay–sand plaster samples absorbed slower than they desorbed, whereas the gypsum wallboard required significantly more time for desorption. Added phytomass gave positive effects by reducing the weight of the clay–sand plaster, accelerating and increasing moisture absorption.

Estimating grassland production loss due to fire for a semi-arid climate

Accidental, runaway veld fires cause enormous fodder flow problems in dry regions. It was the objective of this study to estimate the short-term (one year) impact of fire over 10 growing seasons (1995/96 – 2004/05) on the productivity (aboveground phytomass and litter) of a semi-arid grassland ecosystem. Fire caused a 41% decrease in basal cover over the first season following burning. On average over the study period the seasonal aboveground phytomass and litter production were decreased significantly, from 1 536 to 1 150 kg/ha and 111 - 42 kg/ha, respectively by fire. Seasonal production losses due to fire varied between 238 and 444 kg/ha. The relationship between aboveground phytomass production loss due to fire and two independent variables, namely seasonal rainfall and fuel load (aboveground phytomass plus litter) before burning, was investigated. One year after an accidental fire the production losses can be accurately (79%) estimated if the fuel load before burning is known. In general, the higher the fuel load before burning, the greater the production loss due to fire. The relationships can also serve as a simple empirical model for managers to determine short-term production loss due to unplanned fires in a semi-arid grassland. This information can serve as a scientific guideline in court cases in estimating production losses in claims for damages caused by fires. Keywords : Aboveground phytomass production; basal cover, fuel load; litter South African Journal of Animal Science Vol. 36 (5) 2006: pp.38-41

The impacts of grazing and rainfall variability on the dynamics of a Sahelian rangeland

The impacts of grazing pressure and rainfall variability on rangeland dynamics have been the topic of much debate. Understanding the combined impact of these two factors is crucial for the development of efficient management strategies for rangelands. In this paper, the impacts of grazing and rainfall variability on the dynamics of a Sahelian rangeland in Northern Senegal are examined. Specifically, the paper assesses their combined impact on species composition, above-ground phytomass production and rain-use efficiency (RUE), on the basis of a 10-year (1981–1990) grazing experiment conducted in the Widou-Thiengoly catchment in the Ferlo, Northern Senegal. The experiment included both a high (0.15–0.20 TLU ha −1, corresponding to current grazing) and a medium (0.10 TLU ha −1) grazing pressure. It is shown that species composition, above-ground phytomass production and RUE markedly differ for these two grazing regimes—and that the differences are most pronounced in years with low rainfall. In dry years, both above-ground phytomass production and RUE are significantly reduced in the plots subject to a high grazing pressure. Consequently, the impacts of high grazing pressures on the productivity of the Ferlo are hardly noticed during years with normal or above normal rainfall, but the rangeland's productivity is strongly affected during a drought. The findings have important implications for the management of rangelands; they indicate that high grazing pressures may increase the vulnerability of rangeland ecosystems and local people to droughts.

Influence of fire on litter production and root and litter turnover in a semi-arid grassland of South Africa

Changes in litter production following back and head fires, some soil characteristics and root and litter turnover were quantified over two growing seasons for a semi-arid grassland. Sampling of litter production took place at approximately bi-monthly intervals to account for major seasonal changes over the 2000/01 and 2001/02 seasons. Soil compaction was determined by a simple rod penetrometer, soil temperature by mercury thermometers and soil-water content by a neutron hydroprobe. Litterfall of 5.88% and 1.13% (as a proportion of annual aboveground phytomass production) for unburnt and burnt grassland, respectively, was obtained. Two seasons following the fire, litter was still 47% lower due to fire. The litter production was not significantly different between the head and back fires. The fire, while causing a lower plant cover over the two years following burning, also significantly increased soil compaction and soil temperature. The biggest difference in soil temperature between burnt and unburnt grassland to a depth of 50 mm was 7 °C. After only two months the soil-water content over the first 900 mm depth decreased by 23% due to burning. Fire lengthened the period for replacement of the total root system by about a year and decomposition of litter by three months. Small changes caused by fire to the fragile ecosystems of semi-arid climates may have long-lasting consequences. The overall effects of fire on belowground systems and the resulting processes that feed back to aboveground systems are complex.

Rangeland degradation in a semi-arid South Africa—I: influence on seasonal root distribution, root/shoot ratios and water-use efficiency

The seasonal trend in root mass, root distribution with depth and root/shoot ratios along a degradation gradient were quantified over a 2 year period (2000/01 and 2001/02 growing seasons) for a semi-arid rangeland. Water-use efficiency (WUE) for each rangeland condition is defined as the quantity of above-ground phytomass produced per unit of water evap-transpired. Sampling was from rangeland artificially maintained in 3 different rangeland conditions viz. good, moderate and poor. Roots were extracted to a depth of 900 with 50mm intervals, using a corer and then separated from the soil by wet sieving. Sampling of both above- and belowground phytomass production including litter, were at approximately bi-monthly intervals to account for major seasonal changes. Most of the grassroots were found in the first 150mm soil layer, but root distribution tended to be more superficial with rangeland degradation. Root mass in semi-arid rangelands are strongly seasonal with the most active growth taking place during March and April, when the aboveground is dormant. Both the above- and belowground phytomass productions decreased by rangeland degradation (p⩽0.01). The growing seasonal (October–March) average root mass to a depth of 900mm was 3185, 2336 and 1162kgha−1, respectively, for rangeland in good, moderate and poor condition, compared to the average above-ground phytomass production over the same period of 2341, 1648 and 695kgha−1. It seems that root mass is greater than above-ground biomass for this semi-arid rangeland, with root production also more sensitive to rangeland degradation than above-ground production. The root/shoot ratios for rangeland in good, moderate and poor conditions ranged between 1.57–3.20, 1.65–3.46 and 2.06–7.14, respectively. Water-use efficiency declined (p⩽0.01) with rangeland degradation. Rangeland in good condition averaged a WUE of 2.97kg above-ground phytomass produced ha−1mm−1 evapo-transpiration. The average litter productions were 99.55, 61.51 and 24.00kgha−1, respectively, for rangeland in good, moderate and poor condition. As a proportion of annual phytomass production, litterfall of 5.35% for rangeland in good condition was obtained. This study is one of few root studies available where different rangeland conditions were evaluated and can serve as guidelines for sustainable utilization of the rangeland ecosystem in semi-arid climate.

Estimating the short-term impact of fire on rangeland productivity in a semi-arid climate of South Africa

The short-term (2 years) influence of fire burning with the wind (head fire) and against the wind (back fire) on the productivity (above-ground phytomass and litter) and fire behaviour were determined over seven growing seasons (1995/96–2001/02) in a semi-arid rangeland. The results showed that head fires had significantly greater flame height and rate of spread than back fires. Fire caused a decrease of 40.5% and 22.5% in basal cover for the first and second seasons after burning respectively. The seasonal above-ground phytomass production and litter were significantly decreased by fire over all growing seasons. Seasonal production losses due to fire varied between 225 and 430 kg ha −1. The relation between above-ground phytomass production loss due to fire, and two independent variables namely seasonal rainfall and fuel load (above-ground phytomass plus litter) before burning, were investigated. The multiple linear regression equations obtained for one ( r=0.89) and 2 years ( r=0.86) after a fire, can be used with great success in estimating seasonal production losses due to fire in semi-arid rangeland.

Effect of burning and mowing on grass and forb diversity in a long-term grassland experiment

Disturbance may be an important determinant of plant community composition and diversity owing to its effects on competitive interactions, resources, dominance and vigour. The effect of type, timing and frequency of disturbance on grass and forb species richness was examined using data from a long-term (> 50 yr) grassland burning and mowing experiment in KwaZulu-Natal, South Africa.Grass species richness declined considerably (> 50%) in the absence of disturbance, whereas forb species richness was unaffected. Annual burning in sites not mown in summer tended to increase grass species richness relative to triennial burning (22% increase) with the reverse being true in sites mown twice in summer (37% decline). Forb species richness declined by 25% in sites mown twice in summer relative to sites mown in early summer only. Disturbance was necessary to achieve maximum grass species richness presumably by removing litter and increasing the availability of light. The interaction of time of mowing in summer (early versus late) and time of burning during the dormant period (spring versus winter) had the most dramatic effect on species richness. Time of burning had no effect on richness in sites mown in early summer, but winter burning resulted in a dramatic decline (27–42%) in richness in sites mown in late summer. This effect may be related to possible greater soil desiccation with this combination of disturbances.Nomenclature: Arnold & De Wet (1993).Abbreviation: AGP = Above-ground phytomass production.

Short-term response in productivity following an unplanned fire in a semi-arid rangeland of South Africa

During the dormant winter period the semi-arid rangeland areas of South Africa are characterized by unplanned fires, either by lightning or negligence by man. The quantification of the impact of burning in terms of the above- and below-ground phytomass production, rain-use efficiency (RUE), crude protein, root/shoot ratios and plant density of the grass sward was conducted in a semi-arid rangeland over 2 years (2000/2001–2001/2002 growing seasons) following an accidental fire. Fire (head fire) had a significant ( p<0.01) influence on plant density. Grass species with larger tufts ( Cymbopogon plurinodis and Themeda triandra) suffered the most dieback due to the fire. The initial advantage in quality (crude protein) accompanying the fire does not neutralize the reduction in half of above-ground phytomass production and poor ( p<0.01) RUE occurring in the first season following the fire. Burnt rangeland takes at least two full growing seasons to recover in terms of above- and below-ground phytomass production, litter and RUE. Fire lowered ( p<0.01) RUE for both growing seasons especially during the first four months. The average RUE was 3.72 and 2.86 kg ha −1 mm −1, respectively, for unburnt and burnt rangeland for the 2 years. Root mass decreased ( p<0.01) by 59% over the first 100 mm depth due to fire. More than 80% of the root mass was found in the top 0–300 mm soil layer. The below-ground growth is more sensitive to burning than above-ground growth. Fire reduced the root/shoot ratio from 1.44 to 1.30. These results can serve as scientific guidelines in claims for damages and short-term risk management of semi-arid rangeland after an accidental runaway fire driven by August winds.

Preliminary results of a stocking rate trial in Lesotho

Forage responses to stocking rates and seasons were determined over a one-year period. The experimental design consisted of three stocking rates namely, light (2.0ha LSU-1), moderate (1.25ha LSU-1) and heavy (0.5ha LSU-1) and four seasons (autumn, winter, spring and summer) combined factorially in a Randomised Complete Block Design with three replicates per treatment. Data collected included aboveground available phytomass production, botanical composition and crude protein content. Total aboveground available phytomass production of forages at the end of the study period was significantly (P<0.05) lower in the heavy stocking rate than in the moderate and light stocking rates. Season significantly (P<0.05) reduced crude protein (CP) from 5.6% CP in summer and 7.8% CP in autumn to 4.2% CP in winter and 4.3% CP in spring. It is concluded that season exerted greater impact on sward productivity than stocking rate.

Short-term response of rangeland botanical composition and productivity to fertilization (N and P) in a semi-arid climate of South Africa

This study examined the short-term response of rangeland to annual (1993/94 to 1996/97 seasons) application of fertilizer [all combinations of 0; 10; 30 and 50 kgha−1nitrogen (N), with 0 and 10 kgha−1of phosphorus (P)] in terms of aboveground phytomass production, crude protein content, seasonal rain-use efficiency (S-RUE), nutrient use efficiency, botanical composition, basal cover and soil compaction. After 4 years of fertilization, the botanical composition of the high N-fertilized plots changed from a climax to subclimax vegetation.Elionurus muticus showed the greatest decrease in frequency (62%) due to N fertilization. Phosphorus fertilization only, had an insignificant (p>0·05) influence on species composition and basal cover over the 4 years. The production increased (p⩽0·01) with the application of N together with P, compared to applying only N (1074vs. 823 kgha−1). The more fertilizer applied, the more sensitive to drought the climax grasses became. Nitrogen and phosphorus fertilization significantly (p⩽0·01) affected S-RUE. The highest S-RUE of 6·64 kg phytomass ha−1mm−1and 0·23 kg crude protein ha−1mm−1were obtained with fertilizer application of 50 kgN plus 10 kgPha−1. On average over the 4 years, nutrient use efficiency with N+P application for all treatments was lower than without P. The increases in plant production per kg N applied, both with and without P were 28·00 and 29·81 kg respectively. Soil compaction increased with increase in N fertilization. These results confirm the vulnerability of native grasses in dry areas, following change in soil fertility.

Quantification of the soil-water balance under different veld condition classes in a semi-arid climate

The monthly herbage production, water-use efficiency (WUE: above-ground phytomass production per unit of evapotranspiration), surface runoff and soil loss were determined on grassland in three different ecological conditions, viz. poor, moderate and good, over a four year (1995/1996 to 1998/1999) period. In addition the same measurements were also made on an undisturbed bare soil surface and a soil cultivated twice per annum, only for the last four years. Herbage production and water-use efficiency decreased (P<0.01) when plant cover was reduced or grassland and soil condition declined. The effect of rainfall on productivity is enhanced as plant composition improves from poor through moderate to good. The highest seasonal WUE of 4.76 kg ha−1 mm−1 occurred in grassland in good condition. The dense plant cover of grassland in good condition provides a situation in which surface runoff and soil loss are lower (P<0.01) than that from grassland in poor condition. Direct evaporation from the bare uncultivated soil surface was on average 69% of the rainfall. These monthly production and water-use efficiency results are of the few, if not the only, data available for the semi-arid climates of southern Africa and can be used with great success in future fodder flow planning.

Spectral estimates of absorbed radiation and phytomass production in corn and soybean canopies

Numerous studies have reported a linear relation between phytomass production and absorbed photosynthetically active radiation (APAR) for a wide range of plant species. Related work has shown that APAR may be estimated from multispectral (visible and near infrared) remotely sensed observations. The combination of these two concepts may provide the basis for development of physically-based agronomic monitoring systems. These concepts are subjected to examination for two primary, mid-latitude crops; corn (Zea mays L.) and soybeans (Glycine max Merr.). Phytomass, green leaf area index (LAI), absorbed PAR, and multispectral reflectance factors of corn and soybean were measured periodically from planting to mid-grain fill in two growing seasons. As green LAI increased, the fractional APAR asymptotically approached a maximum value between 0.95 and 0.97. Fractional APAR displayed a linear relation to the normalized difference vegetation index (NDVI), which is relatively independent of species, throughout the growing seasons. However, deviations in the relation were observed between pre- and post-onset of senescence. For both corn and soybean, a linear relation between cumulative APAR and cumulative aboveground phytomass production was found. However, the rate of accumulation per unit APAR was more than twice as great for corn as for soybean. This agrees with previous reports comparing C 4 grasses and C 3 legumes. These results indicate that remotely sensed measurements contribute valuable information concerning energy / mass accumulation in plant canopies. However, implementation of this approach in crop monitoring will clearly require a capability to discriminate between, at least, corn and soybean. The influence of stress events, such as drought, nutrient limitations, and disease, will also require further consideration.