Physical rehabilitation of degraded krasnozems using ley pastures

Abstract

The physical fertility of krasnozems and euchrozems (Red Ferrosols) in Australia has declined substantially as a result of continuous cropping. Much of this decline is associated with reduced levels of soil organic carbon and soil compaction due to vehicle trac when soils are too wet. We examined the impact of kikuyu (Pennisetum clandestinum) and Rhodes grass (Chloris gayana) pasture leys with various management inputs on the regeneration of physical fertility of continuously cropped krasnozems from 2 locations in the South Burnett region of southern Queensland. Pasture leys significantly improved the physical fertility of continuously cropped soils within 2–4 years. The most significant effects were on the creation of improved surface and subsurface macroporosity, and in a reduction in surface crust formation under high energy rain due to improved aggregate stability. Final steady state infiltration rates under well-managed leys increased 4-fold compared with those in continuously cropped soil. Pastures were unable to ameliorate compacted layers below approx. 15 cm, although significant improvements in hydraulic conductivity through these layers (and to depths of at least 70 cm) were made, presumably by creating of continuous biopores. Introduced earthworms improved pasture effectiveness in ameliorating this layer, but only to depths of 20 cm, while deep ripping during the ley phase was the most effective treatment. Kikuyu was the more effective pasture species in overcoming soil physical infertility, particularly in terms of improving aggregate stability under rain. In addition, the ability of kikuyu to resist the compacting influence of cattle trampling during wet weather meant that rainfall infiltration eciency was maintained during the ley phase and management options on returning to cropping were more flexible (e.g. direct drill strategies can be used). However, if pastures were ungrazed, the advantages of kikuyu in soil physical restoration were evident in only 2 years.

Rapid internal drainage rates in Ferrosols

“…A kikuyu pasture was established on part of the area, with a detailed description of treatments and management outlined previously (Bell et al 1997). Briefly, the pasture plots were not cut or grazed during the next 4 years, while 4 management regimes were imposed: (i) low input pasture, where no fertiliser or other inputs were supplied; (ii) fertilised pasture, where annual applications of N, P, and K fertiliser were made; (iii) fertilised ripped pasture, where the soil was ripped to a depth of 0.35-0.40 m during year 2 of the ley; and (iv) fertilised pasture with earthworms, where locally adapted earthworms (Fletcherodrilus unicus, Aporrectodea trapezoides, and Potoscolex corethurus) were introduced during the initial year of pasture establishment.…”

“…Data were analysed using the method of Reynolds and Elrick (1991), which allowed estimates of the saturated hydraulic conductivity (K sat ) to be derived. There were 8 measurements for each treatment (Bell et al 1997), with measurements made at Goodger on an annual basis from 1994 to1999.…”

“…One common characteristic of these soils after longterm cropping is a loss of the original very high rainfall infiltration capacity-a key factor in successful rain-fed cropping (Bridge and Bell 1994). This has been attributed to 2 factors: firstly, a decline in labile organic carbon resulting in surface crusting, and secondly, subsoil compaction that reduces the hydraulic conductivity down the profile (Bell et al 1997(Bell et al , 1998.…”

“…The use of kikuyu (Pennisetum clandestinum) and Rhodes grass (Chloris gayana) pasture leys were shown by Bell et al (1997) to dramatically improve soil organic matter contents in the upper 0.30 m and infiltration rates into the soil profile. Unfortunately, subsequent experimental crops were unable to capitalise on the improved infiltration rates because of the relatively low available water capacity, around 0.1 cm 3 /cm 3 (Bridge and Bell 1994;Bell et al 2001).…”

Sistemas de manejo do solo na recuperação de uma pastagem degradada em Rondônia

“…Dentre os parâmetros físicos do solo mais utilizados para avaliar a degradação de pastagens, destacam-se a densidade do solo (Muller et al, 2001;Fidalski et al, 2008), o sistema poroso (Fidalski et al, 2008;Cardoso et al, 2011), a resistência do solo à penetração de raízes (Imhoff et al, 2000;Ralisch et al, 2008;Cardoso et al, 2011) e as caraterísticas da água no solo (Bell et al, 1997;Dias Junior & Estanislau, 1999;Fidalski et al, 2008). O aumento da densidade e resistência do solo à penetração de raízes foi observado por Corrêa & Reichardt (1995) em uma sucessão floresta-pastagem, quando comparado aos dados obtidos na área de floresta.…”