Fallow Time Research Articles

Carbon and nitrogen dynamics in two soils with different fallow times in the high tropical Andes: indications for fertility restoration

In the upper agricultural belt of the tropical Andes, above 3000 m of altitude, long fallow agriculture is commonly used to produce potatoes and cereals. This agricultural system alternates short intervals of production (2–4 years) with long fallow periods (generally 5–10 years or more). In order to analyse soil changes related to the rapid fertility loss during the production interval and soil fertility restoration during the fallow period, the soils of two adjacent but contrasting plots were compared. One plot had passed through 15 years of fallow (restored) and the other had been cultivated with potatoes for three consecutive years after a 12 years fallow period (depleted). The soils were analysed for fresh C- and N-microbial biomass, inorganic N and physical–chemical properties. Then, the soils were incubated under controlled laboratory conditions for 81 days, with and without the addition of 14 C labelled wheat straw. During the incubation, periodic measurement of C– and 14 C –CO 2 release, C- and 14 C -microbial biomass, N-microbial biomass and inorganic N were performed. The most pronounced difference between the fresh soils was in the microbial biomass, which was almost double the amount in the restored soil with respect to the depleted soil. During the incubation, the total amounts of soil native C and N mineralised were significantly higher in the restored soil. Also the mineralisation of the added 14 C -labelled straw was faster in the restored than in depleted soil. These results suggest that the fallow period leads to an increase in the labile C and N pools and microbial biomass, which represent more carbon and nitrogen availability for microorganisms and plants and could be related to fertility restoration. A very high stability of the organic matter in these mountain soils was also revealed and its implications for agricultural sustainability are discussed.

The contribution of Paraserianthes (Albizia) falcataria to sustainable swidden management practices among the Baduy of West Java

There is a prohibition on the use of modern external inputs, such as chemical fertilizers, in Baduy swidden farming. Ordinarily, the consequence of this in a situation of acute forest pressure would be a decrease in fallow times, and an inevitable depletion of soil fertility. The Baduy (particularly Outer Baduy) have several ways of alleviating this problem, one of which is the introduction of Paraserianthes (Albizia) falcataria. By alternating this commercially valuable perennial leguminous tree with rice, soil fertility is maintained and the socio-economic position of the Baduy improved. As a result, swidden farming, which is considered by the Baduy to be central to their cultural identity, continues to be viable, despite increasing population density and the continuing depletion of mature forest.

Effects of forest disturbance on the structure of ground-foraging ant communities in central Amazonia

This study evaluates biotic responses, using ants as bio-indicators, to relatively recent anthropogenic disturbances to mature forest in central Amazonia. The structure of the ground-foraging ant community was compared in four habitats that represented a gradient of disturbance associated with differences in land use. Ants were collected in undisturbed, mature forest, in an abandoned pasture, in a young regrowth forest (situated in a former pasture area), and in an old regrowth forest (established where mature forest was just cleared and abandoned). More ant species were found in mature and old regrowth forest than in the abandoned pasture. By contrast, ant abundance tended to decrease with forest maturity. Both pasture and young regrowth forest exhibited a distinct ant species composition compared to mature forest, whereas species composition in the old regrowth forest showed greater similarity to that of mature forest. In spite of differences in fallow time between former pasture areas and non-pasture areas, there is evidence that different land-management practices do result in different rates of recovery of the ant forest fauna after land abandonment. In any case, recuperation of the ground-foraging ant fauna appears to be faster than regeneration of the woody-plant community. In this sense, regrowth forests may be valuable for the conservation of ground-foraging ants and perhaps for other components of mature-forest leaf-litter fauna within the context of a fragmented landscape.

Cropping and Tillage Systems for Dryland Grain Production in the Southern High Plains

AbstractLow precipitation and high evaporative potential limit yields of dryland crops in the semiarid Southern High Plains. Improved residue management can reduce evaporation and improve water conservation. We compared no‐tillage (NT) and stubble mulch (SM) residue management effects from 1984 to 1993 on leveled minibenches at Bushland, TX, using winter wheat (Triticum aestivum L.)‐fallow (WF), continuous wheat (CW), wheat‐sorghum [Sorghum bicolor (L.) Moench]‐fallow (WSF), and continuous sorghum (CS) systems. The soil was a Pullman clay loam (fine, mixed, thermic Torrertic Paleustoll). Our objective was to quantify and compare soil water storage, crop water use, and grain production in order to identify the most water‐efficient production system. Relative to SM management, NT management of wheat residues increased average soil water contents at planting of the next crop by 22 mm with WSF, 15 mm with WF, and 29 mm with CW; it was not as effective with sorghum residues. Mean grain yields were not affected by residue management on any cropping system, because the additional water stored with NT management was slight in relation to seasonal evapotranspiration. Cropping systems had major effects on grain yield and production. Fallow systems (WSF, WF) normally resulted in higher yields than the corresponding annual cropping system (CW, CS). However, when grain production was adjusted to an annual basis including fallow time, the CS system was most efficient at using precipitation, producing 92% more grain than WSF, 240% more than CW, and 320% more than WF. Grain production was more than twice as great with sorghum than with wheat, due to greater biomass production and a 33% greater harvest index. Although wheat is the major dryland crop in the Southern High Plains, sorghum seems much better adapted to the region's predominant pattern of late spring‐summer rainfall.

Rehabilitation of degraded lands by means of fallowing in a semi-arid area of northern Nigeria

Land degradation in semi-arid regions of Nigeria is a very serious problem and therefore rehabilitation of degraded lands is essential. This article reports the results of an investigation which was carried out to assess the extent to which fallowing rehabilitates degraded lands in a semi-arid area in northern Nigeria. An inferential approach was used which involved side-by-side comparison of plots located within an area of uniform climatic, geologic and geomorphic characteristics, but which have been under fallow for different periods of time (2, 5, 10 or 15 years). Using a systematic sampling procedure, topsoil and subsoil samples were collected from each of the fallow plots and also from a plot under a plant community of well over 80 years of age which was chosen to serve as the control (fairly natural vegetation). The extent to which the land of each fallow plot had been rehabilitated could be assessed by comparison with the condition of the control plot. The samples were analysed for texture, bulk density, water-stable aggregates greater than 0.50 mm, moisture content, organic matter, pH, cation exchange capacity (CEC), total nitrogen, available phosphorus and exchangeable bases. An analysis of variance (ANOVA) technique was used to test for significant differences amongst the fallow plots, while Student's t-test was used to compare the mean values of the soil properties of the control with the same properties under each of the fallow plots. The results obtained varied considerably, but in general it was observed that there were decreases in the coarsening of soil texture and bulk density, but increases in other soil properties with increases in the length of the fallow period. However, the changes were generally found to be more significant under the older fallows (10 and 15 years) than under the newer fallows (2 and 5 years). The causes of these trends and their implication for sustainable land development in the area are discussed. It is concluded that for land rehabilitation to be effective in this area, either fallow times must be quite long, or ways of improving the soil's recuperative capacities under short-term fallow should be sought.

Minimum duration of effective head-only electrical stunning of fallow deer (Dama dama) and time to loss of consciousness following a throat-cut

Abstract Extract Recent work(1) (2) has demonstrated the success of headonly electrical stunning in both red (Cervus eluphus) and fallow (Dama dama) deer. This work has been extended to investigate the export market and welfare requirements of the minimum duration needed for successful stun and the time to loss of consciousness following a throat-cut (severance of both carotid arteries and jugular veins) alone in fallow deer.

Nitrogen Nutrition of Rainfed Winter Wheat in Tilled and No‐Till Sorghum and Wheat Residues

AbstractDecomposition of sorghum [Sorghum bicolor (L.) Moench] and wheat (Triticum aestivum L.) plant residues can immobilize enough surface‐applied N to cause a deficiency in successive winter wheat crops. This experiment examined the effects of conventional and no‐till grain sorghum and wheat residues on N requirements of dryland winter wheat. Field experiments conducted from 1987–1991 on an Austin silty clay (fine‐silty, carbonatic, thermic Udorthentic Haplustoll) soil included sorghum and wheat residue treatments with conventional till (CT), no‐till (NT), and residue removal (RR). All residue plots received four preplant N rates (0, 45, 90, and 135 kg N ha−1), with subplots planted to three winter wheat cultivars in 1988 and 1989, and two cultivars in 1990 and 1991. Grain and stover yields were significantly lower when wheat followed sorghum than under continuous wheat. Wheat grain yields at N application rates < 90 kg ha−1 were 39% lower in NT plots vs. CT plots, 5% lower in CT plots compared with yields in RR plots, and 39% lower in sorghum‐wheat rotation compared with continuous wheat. Wheat N uptake at N application rates <90 kg ha−1 was 41% lower in NT plots vs. N uptake in CT plots, 10% lower in CT plots vs. N uptake in RR plots, and 36% lower in sorghum‐wheat rotation vs. continuous wheat. Grain yield and N uptake of wheat at the 135 kg N ha−1 rate were not significantly different in NT and CT plots. Preplant soil NO3‐N analysis indicated a need for the application of N fertilizer at planting in CT and NT sorghum residues, and basal stem NO3‐N analysis showed wheat growing in NT residues and sorghum‐wheat rotations; had higher N fertilizer requirements than continuous CT wheat. Microbial immobilization of surface‐applied N was responsible for N deficiencies observed in NT winter wheat, while a decrease in fallow time between sorghum harvest and wheat planting dates was the primary cause for reduced mineralization rates of residue‐derived and indigenous soil N in sorghum‐wheat rotations. A fallow period following grain sorghum and/or band application of fertilizer N could alleviate N deficiencies observed in this study.

Twill

Twill (for Nancy, weaver & friend) Cat track, snail trail— We too ply the wild rose path to the pine tree and back, intending this hour for indigo blue, the warp in our thoughts leveled, conceits shed, and sticky egos dissolved. Walk at this curiously fallow time of day, past querulous cows, and dogs straining at our scent— poised and empty, smiling at even the unexpected S untwisting just ahead. There is no web that can trap us, or hook that can hold us apart: We are nubs in the emerald algae's loose weave on the pond, as much our neighbor's tabby prowling the brake as cricket shuttling through the weedy selvage of the path. Cat track, snail trail— no destination but the pine. Our only harness is the breeze. —Anne Richey 49 ...

Manipulating spatial and temporal resources in agro‐ecosystems: environmental inputs to resource management

When intensified agro‐ecosystems are compared to subsistence systems three major differences are apparent. In intensified agro‐ecosystems, genetic homogeneity is increased, stock levels are increased, and fallow time is reduced. These changes alter the amount, type, and rate of resource allocation. The paper supports the position that planners can manipulate species diversity and space‐time parameters to effectively partition resources in ways that will increase harvestable biomass and enhance ecological stability. Community interactions and succession patterns can be adjusted to help minimize topsoil deterioration and resource depletion. Specific agricultural techniques are presented to aid agriculturalists to develop long‐term sustainable agro‐ecosystems.

A stochastic model for estimating human carrying capacity in Brazil's Transamazon Highway colonization area

Human carrying capacity for tropical agricultural populations can be estimated with a computer simulation of the agroecosystem. A stochastic model is developed for estimating carrying capacity in one of the government-directed small farmer settlement projects along Brazil's Transamazon Highway. Carrying capacity is operationally defined in terms of an empirically computed relationship between population density and probability of colonist failure with respect to various criteria. When high population density leads failure probability to exceed a maximum acceptable level, population can be considered to be above carrying capacity. Colonist failure probabilities are those that are sustainable over a long period of simulated years. High variability in crop yields appears to have a strong effect on failure probability based on comparison of deterministic and stochastic runs of the simulations. Failure probabilities are raised by variability at low population densities, but are lowered at extremely high densities where most colonists would fail in an “average” year. Effects can be tested for colonists with different backgrounds or with differing agricultural practices such as fallow times. Failure probabilities in standard runs are higher than those considered acceptable to government planners at all population densities simulated in the present study's stochastic runs (lowest density 24 persons/km2), thus lending support to the informal impression of many that the carrying capacity of most of Amazonia's uplands is low.