Browsing by Autor "R. G. Barber"

Now showing 1 - 8 of 8

Compaction status and compaction susceptibility of alluvial soils in Santa Cruz, Bolivia
(Elsevier BV, 1989) R. G. Barber; Camilo Saavedra Herrera; Olga Díaz Rubio
Effects of Bulldozer and Chain Clearing on Soil Properties and Crop Yields
(Wiley, 1994) R. G. Barber; Danilo Jefferson Romero
Abstract The use of bulldozers and straight blades for clearing subtropical forests in eastern Bolivia is believed to result in serious soil degradation and low crop yields. It was hypothesized that chain felling with a tree pusher and rake windrowing would cause less soil degradation and give higher crop yields. An experiment established on a Typic Haplustalf compared the effects on soil degradation and subsequent crop yields of (i) conventional bulldozer felling and windrowing with a straight blade (land clearing control), (ii) bulldozer felling with a straight blade and tree pusher, and rake windrowing, (iii) chain felling with a tree pusher and straight blade windrowing, (iv) chain felling with a tree pusher and rake windrowing, and (v) undisturbed forest (control). All four methods caused significant soil physical degradation as manifest by 10 to 20% increases in bulk density and a 6.2% loss of total porosity at the 0‐ to 0.20‐m depth, a lowering of the soil surface by about 30 mm due to compaction, and a significantly lower 30‐min cumulative infiltration (4.36 cm) compared with the forest control (15.08 cm). All four land clearing methods gave significant increases in Ca (from 7.7 to 11.6 cmol c kg −1 ) in the 0‐ to 0.20‐m depth as a result of forest burning. Very few significant differences in soil properties, and no significant differences in subsequent yields of corn ( Zea mays L.) or soybean ( Glycine max. L.), were found among land clearing methods. Thus, under dry to slightly moist soil conditions and with skilled operators, the clearing of a low‐biomass, subtropical forest by bulldozer clearing with a straight blade was no more degrading to the soils than chain felling with a tree pusher and rake windrowing, and did not result in lower yields of subsequent crops.
Effects of conservation and conventional tillage systems after land clearing on soil properties and crop yield in Santa Cruz, Bolivia
(Elsevier BV, 1996) R. G. Barber; Mabel Orellana; Francisco B. Navarro; Olga Díaz Rubio; M.A. Soruco
Effects of deep tillage and fertilization on the population, growth and yield of soya during an exceptionally wet season on a compacted sandy loam, Santa Cruz, Bolivia
(Elsevier BV, 1990) Mabel Orellana; R. G. Barber; Olga Díaz Rubio
Effects of deep tillage on soil properties, growth and yield of soya in a compacted ustochrept in Santa Cruz, Bolivia
(Elsevier BV, 1989) Leovânio Rodrigues Barbosa; Olga Díaz Rubio; R. G. Barber
Evaluation of the characteristics of 14 cover crops used in a soil rehabilitation trial
(Wiley, 1994) R. G. Barber; Francisco B. Navarro
Abstract Many of the soils in Santa Cruz Department, Bolivia, are degraded by serious weed infestation, subsoil compaction, and low organic matter and nitrogen contents. Fallow periods with cover crops are frequently used to recuperate the fertility of degraded soils, but little information exists on the desired characteristics of cover crops for this purpose. The aim of this study was to describe those characteristics, believed to be most relevant to the rehabilitation of degraded soils in Santa Cruz, of 14 cover crops, which included three grasses, nine legumes, and two winter cover crops sown after summer soybean ( Glycine max ). The cover crop characteristics, evaluated over two years, were ease of establishment, competitiveness against weeds, tolerance to drought, dry matter production and nutrient contents of the above‐and below‐ground residues, nodulation, rooting density and root diameters. The three grasses Tobiata ( Panicum maximum var. Tobiatd), Centenario ( Panicum maximum var. Centenario) and Brizantha ( Brachiaria brizantha ) appeared to be the most promising for increasing soil organic matter contents, and the three grasses and groundnuts ( Arachis hypogaea )/pigeon pea ( Cajanus cajan ) for the recuperation of subsoil structure. Mucuna deeringiana and Lablab (Dolichos lablab) were the most promising for increasing soil N status. All of these cover crops competed successfully with weeds.
Maintenance of Yields and Soil Fertility in Nonmechanized Cropping Systems, Bolivia
(Wiley, 1994) R. G. Barber; Olga Díaz Rubio
Abstract Slash and burn farmers in the tropical rain forests of eastern Bolivia are abandoning land after one rice ( Oryza sativa L.) crop because of declining yields. A trial was conducted on a Typic Paleudult for 41 mo to investigate whether alternative low‐input nonmechanized cropping systems could prolong soil fertility and yield maintenance, and whether soil fertility or weeds were responsible for declining yields. Twelve cropping systems were investigated in a factorial design, with three summer‐winter crop sequences: rice‐peanut ( Arachis hypogaea L.), corn ( Zea mays L.)‐bean ( Phaseolus vulgaris L.) later substituted by cowpea [ Vigna unguiculata (L.) Walp.], and rice‐fallow (control); two weed control treatments: minimal and optimal; and two fertilizer treatments: with and without 60 kg N ha −1 and 17.5 or 35 kg P ha −1 . Crop sequences significantly increased exchangeable acidity; the rice sequences significantly reduced exchangeable Ca, and corn‐bean/cowpea and rice‐peanut significantly reduced exchangeable Mg. Fertilization significantly increased soil P but decreased Ca. Foliar analysis revealed N, Mg, and Zn deficiencies in all cropping systems. Rice yields, unlike corn, were significantly increased by optimal weeding. Corn yields were dominated by fertilization, whereas rice yields were mainly influenced by fertilization in the first and fourth years, and by weeds in the intervening years. Without fertilizers, rice‐fallow was not sustainable, and only corn‐bean/cowpea was sustainable for 3 yr. With fertilization, rice‐fallow plus optimal weed control and corn‐bean/cowpea with minimal or optimal weeding were sustainable for 3 yr. Additional fertilization and future liming would be necessary for more prolonged sustainability.
The rehabilitation of degraded soils in eastern bolivia by subsoiling and the incorporation of cover crops
(Wiley, 1994) R. G. Barber; Francisco B. Navarro
Abstract A high proportion of the soils in the central zone of Santa Cruz, eastern Bolivia, are chemically and physically degraded, with low organic matter and N contents, compacted subsoil layers and a propensity to crusting, hardsetting and wind erosion. The aim of the experiment discussed in this paper was to identify suitable cover crops to be used in combination with subsoiling for the rehabilitation of degraded soils and the improvement of crop yields in eastern Bolivia. Fertilizers were not used because of their high cost. An experiment with a split complete block design, with subsoiling and no‐subsoiling as the main treatments, 14 cover crops and a continuously cultivated soybean/wheat control as the subtreatments, and four replications, was established on a degraded site comprising a mosaic of two compacted siliceous isohyperthermic soils (a coarse loamy Typic Ustropept and a fine loamy Typic Haplustalf). After a two‐year fallow period, the cover crops were incorporated and test crops were sown for five seasons to evaluate the effects of the treatments on subsequent crop yields. Soil samples were taken to measure changes in chemical fertility. The only significant cover crop effect on soil nutrients was an increase in exchangeable K from 0.47 to 0.56 cmol c kg −1 by Lablab; subsoiling had no effect on chemical fertility. For all treatments there was an average 24 per cent increase in soil organic matter from 13.1 g kg −1 at 3 months after cover crop incorporation to 16.3 g kg −1 at 19 months after incorporation. No significant differences in total N were found during this period. Test crop yields were not influenced by subsoiling, but were significantly increased by some of the cover crops as compared to the soybean/wheat control during the first three seasons only. Evidence from foliar analysis suggests that the effects of the cover crops on soybean yields were not nutritional and so presumably were physical in nature, whereas the benefits on wheat yields were possibly related to increased N availability. Panicum maximum var. Centenario and P. maximum var. Tobiatá gave the highest total yield increases over the first three cropping seasons (101 and 85 per cent, respectively), but these yield increases would not compensate the farmer for the loss of four crop harvests whilst the land was in fallow. These results highlight the difficulties of rehabilitating soil fertility and increasing crop yields through the use of subsoiling and cover crop fallows on compacted, low organic matter soils in eastern Bolivia.