摘要:

Computer simulation, point‐based field sampling procedures, and step‐wise multiple linear regression were used to establish a relationship between the basal cover (BC) of a sample site and paired observations of the mean distance from a point to the nearest living tuft (D) and the mean basal diameter of the tufts (d). The model may be summarized as:

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638327

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Soils in the study, carried out in the Texas Trans‐Pecos region, were fine‐loamy, mixed, thermic Aridic Calciustolls; fine‐loamy, mixed, thermic Aridic Ustochrepts; and fine, mixed, thermic Typic Chromusterts. Our primary objective was to determine the effect of three grazing intensities within an intensive, short‐duration grazing system on selected soil physical properties. Maximum compaction occurred in the A2/AB horizons, which has significantly higher (P<0.05) penetrometer readings than the overlying A I/A horizons under all grazing intensities. Heavily grazed areas also have significantly higher (P<0.05) penetrometer reading than the other two areas in both horizons. Heavily grazed areas also have significantly lower (P<0.05) infiltration rates, saturated hydraulic conductivities, and water‐stable aggregates than soils grazed at the other two levels. Aggregates in the A2/AB horizon were more stable than aggregates in the Al and Bw horizons in every pedon under all grazing intensities. When the effect of grazing intensity was analysed for each horizon separately, the lightly grazed areas had significantly lower (P<0.05) bulk density and higher total porosity in the A2/AB horizons than comparable horizons from the other two sites. However, when all horizons were analysed together, no significant differences in bulk density were found among treatments and horizons. No significant differences were observed in percentage organic carbon among treatments.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638328

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The pattern of nitrogen (N) loss through volatilization as ammonia (NH3) may have important fertilizer management implications. A micrometeorological mass balance was used to measure this pattern after application of limestone ammonium nitrate (LAN; 28% N) and urea (46% N). Variables monitored included air temperature, relative humidity (RH), wind speed, and rainfall. The influence of these variables on patterns of NH3loss was assessed graphically and by using Spearman's ranked correlation analysis. A daily pattern of loss was observed in the flux of NH3, with the greatest losses occurring between 10h00 and 14h00 on every sampling day. High temperatures and wind speeds promoted losses whilst rainfall events (in excess of 5 mm) inhibited losses, apparently by transporting applied fertilizer into the soil profile. Losses were suppressed at low temperatures, low wind speeds, and highRH. The highest overall loss recorded (3.7% of applied N) was lower than that expected for sub‐tropical conditions.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638329

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Using a micrometeorological mass balance method, a study was undertaken to assess volatilized nitrogen (N) losses during and after the grazing of drylandPennisetum clandestinumHochst. (kikuyu) pastures. Specific objectives were to measure the magnitude of volatilized N loss and to establish the pattern of volatilized N loss over time. Nitrogen losses measured over a period of 120 h ranged from 88 to 946 g N ha‐1(at a stocking rate of 3 AU ha‐1), and from 240 to 2 685 g N ha‐1(at a stocking rate of 6 AU ha‐1stocking rate). In terms of achieving lower losses, the mean difference in N lost as NH3was in favour of the lower stocking rate (3 AU ha‐1), estimated at 1 051 ± 324 g NH3ha‐1(P≤0.05). A consistent pattern of NH3loss was shown to occur during the season, with higher losses being recorded during the day time and lower losses at night.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638330

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Relative abundances of rangeland species have for many years been used to index trends in range condition following the impact of grazing. All species recorded in a botanical survey are usually classified according to their assumed reaction to grazing using the increaser and decreaser groups. We used a gradient analysis of 216 sample sites to show that only certain species in the Highland Sourveld of Natal, South Africa, were responsive to the grazing impact. We therefore recommend that non‐responsive species should not be used to monitor trends in range condition. Three categories of grass species were defined for interpretive purposes in a monitoring programme, viz. decreaser, increaser and invader species, based on their reaction to the grazing impact. Eight grass species in the Highland Sourveld of Natal showed clear responses along a gradient of grazing intensity, and were abundant over at least a portion of this gradient. These species were selected as key species and were recommended for monitoring range condition in this vegetation type.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638331

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Tswana steers were continuously grazed at stocking rates of 3, 6, and 9 ha LSU‐1in two blocks, and steers in one block were supplemented with phosphorus. Dry matter yield of herbaceous rangeland plants was measured at the end of each growing season from 1984 to 1990 except in 1986, whilst steer livemass was measured monthly. Steers entered the trial at the beginning of the growing season and remained on the trial for three years and two groups of steers were evaluated in the study. Dry matter yield ofDigitariaspp. and annual grasses showed no response to stocking rate.Panicum maximumandEragrostis rigidiorwere the most responsive species, increasing with a decreased stocking rate. Phosphorus supplement was advantageous during drought periods at stocking rates higher than 9 ha LSU‐1. Livemass gain increased with decreased stocking rate regardless of phosphorus supplement.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638332

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The effect of maintaining veld in three conditions,viz. poor, moderate and good, for 15 years, on the organic carbon (C) and total nitrogen (N) content (as measures of organic matter content) of a fine sandy loam soil was investigated. Composite soil samples were collected and analysed to a depth of 300 mm at 50‐mm depth intervals from plots with the imposed veld conditions. The organic C and total N content of the soil under the three veld conditions differed significantly (P<0.05). Both variables declined as the veld condition degraded. Total N differed less than organic C. The largest differences were measured in the 0–50 mm layer and the smallest in the 250–300 mm layer. Losses of soil organic matter can be attributed to reduced phytomass production, increased soil erosion and change in soil climate. It is suggested that the loss of soil organic matter from degraded veld may inhibit veld recovery.

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638333

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638334

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:1022-0119    

DOI:10.1080/10220119.1993.9638326

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor