Desertification : Concept, causes and amelioration

Desertification is a condition of human-induced land degradation that occurs in arid, semiarid and dry sub-humid regions (precipitation/potential evapotranspiration or P/ETP 0.05 to 0.65) and leads to a persistent decline in economic productivity (> 15% of the potential) of useful biota related to a land use or a production system. Climatic variations intensify the decline in productivity, restorative management mitigates it. Drylands or territories susceptible to desertification occupy 39.7% (~ 5.2 billion ha) of the global terrestrial area (~ 13 billion ha). The highest concentration of drylands occurs in Africa, Asia and Australia. Two out of every three hectares of drylands suffer from land degradation of one kind or another. Barring 78 M ha which are irreversibly degraded, the remainder area - affected by desertification - is reclaimable at a price. Desertification is caused primarily by over-exploitation of natural resources beyond their carrying capacity. Solutions to combat desertification lie in the management of the causes of desertification. However, there are no easy options to combat it. While managing demographic pressure should receive priority, the solutions to combat desertification involve local action, guided by land use and climatic conditions and in harmony with local needs and people’s expectations. Drylands are used as rangelands or as croplands, with the latter either irrigated or rainfed. Integrated data on land and soil degradation and on the socio-economic environment within which it occurs are the basis to formulate strategies for reclamation and proper use of drylands. Rangelands constitute the dominant land use (est. 88%) in the territories susceptible to desertification. Of the 3333 M ha rangeland area affected by land degradation 757 M ha are severely affected., 72 M ha irreversibly. Within rangelands, vegetation degradation is the primary cause of desertification – it represents 72% of the total area desertified worldwide (2576 M ha out of 3592 M ha). Overgrazing by excessive numbers of low productivity livestock and fuel wood extraction by man are the principal causes of vegetation degradation. Centralized management of common rangeland resources and insecure tenancy laws stand in the way of communities and herders adopting a long-term view to conserve and invest in range improvement measures. Inadequate dissemination of knowledge on vegetation improvement methods is another cause of rangeland degradation. Five suggestions are made to assure sustainability and effectiveness of rangeland management programs: (1) shifting to community management of rangelands that have been nationalized, (2) granting formal rights to individual transhumance herders that have been settled, (3) providing education and training on range management and improvement, (4) introducing elite breeds of livestock for high productivity, and (5) implementing programs for harnessing alternative sources of energy for cooking (solar and biogas). Rainfed croplands occupy an area of 457 M ha, 216 M ha of which have degraded soils. Some 4 M ha suffer from irreversible degradation. Of the remainder, 29 M ha and 183 M ha are, respectively, affected by severe (reclaimable with engineering works) and moderate degradation. Soil constraints in rainfed croplands arise primarily from their vulnerability to erosion, which leads to loss of organic matter, fertility and rooting depth. Eroded soils are structurally unstable and are prone to crusting and compaction. Risk arising from drought susceptibility and poverty limit the adoption of restorative management. Rainwater conservation to minimize risk is not adopted due to insecure tenancy and centralized management of government supported programs. A lack of adequate knowledge and skills of efficient use and storage of rainwater allow degradation processes to proceed unchecked. The imperatives to succeed are: (1) land tenure policies towards freehold ownership; (2) community participation in the management of rainwater, (3) efficient use of harvested water supported by high value land use options built on indigenous knowledge and (4) government support to facilitate the development of rainfed agriculture. Irrigated croplands occupy an area of 145 M ha. Of this, 2 M ha are affected by irreversible degradation and 41 M ha suffer from reversible degradation, mainly from salinity and waterlogging. The mechanisms of salinity development differ and so do the solutions when canal or underground water is used for irrigation. With canal water irrigation, three key development options are suggested to remove excess salts and water and to minimize conveyance and application losses of water: (1) effective drainage, (2) properly lined or closed water conveyance systems and efficient irrigation techniques, and (3) participatory management of irrigation systems. The costs of installing drainage and leak-proof conveyance systems are high, but so are the economic and ecological gains. With underground water use, salinity develops as the water reserves are depleted due to over-extraction. While efficient methods of irrigation can help in postponing the occurrence of salinity, sustainable solutions lie in balancing the water withdrawals with recharge. Efforts should therefore be made to promote groundwater replenishment through runoff harvesting. Although it is not always possible to recharge the deep aquifers with the limited quantities of runoff produced by the low annual precipitation, still, the use of harvested runoff for irrigation can save groundwater. Once water-efficient systems are operational, cropping systems that maximize productivity per unit of water can be introduced. The entire strategy of reclaiming desertified land revolves around water, the reestablishment of the vegetation of rangelands, the rejuvenation of the productivity of rainfed croplands, and the halting of loss of irrigated farmlands. Humans play a central role in that strategy; desertification begins and ends with human action. Unless it ends, the estimated 900 million people affected today will grow to billions tomorrow

Representing and Evaluating Legal Narratives with Subscenarios in a Bayesian network

In legal cases, stories or scenarios can serve as the context for a crime when reasoning with evidence. In order to develop a scientifically founded technique for evidential reasoning, a method is required for the representation and evaluation of various scenarios in a case. In this paper the probabilistic technique of Bayesian networks is proposed as a method for modeling narrative, and it is shown how this can be used to capture a number of narrative properties. Bayesian networks quantify how the variables in a case interact. Recent research on Bayesian networks applied to legal cases includes the development of a list of legal idioms: recurring substructures in legal Bayesian networks. Scenarios are coherent presentations of a collection of states and events, and qualitative in nature. A method combining the quantitative, probabilistic approach with the narrative approach would strengthen the tools to represent and evaluate scenarios. In a previous paper, the development of a design method for modeling multiple scenarios in a Bayesian network was initiated. The design method includes two narrative idioms: the scenario idiom and the merged scenarios idiom. In this current paper, the method of Vlek, et al. (2013) is extended with a subscenario idiom and it is shown how the method can be used to represent characteristic features of narrative

Effect of Zai Soil and Water Conservation Technique on Water Balance and the Fate of Nitrate from Organic Amendments Applied: A Case of Degraded Crusted Soils in Niger

Experiments were conducted on degraded crusted soils to study water status and nitrogen release in the soil during the dry seasons of 1999 at ICRISAT research station and on-farm during the rainy seasons of 1999 and 2000 in Niger. Zai is a technology applied on degraded crusted soil, which creates conditions for runoff water harvesting in small pits. The harvested water accumulates in the soil and constitutes a reservoir for plants. The organic amendment applied in the Zai pits releases nutrients for the plants. Soil water status was monitored through weekly measurement with neutron probe; access tubes were installed for the purpose. Nutrient leaching was measured as soil samples were collected three times throughout the cropping season. A rapid progress of the wetting front during the cropping period was observed. It was below 125 cm in the Zai-treated plots 26 days after the rain started versus 60 cm in the non-treated plots. Applying cattle manure leads to shallower water profile due to increased biomass production. Total nitrate content increased throughout the profile compared to the initial status, suggesting possible loss below the plant rooting system due to drainage, which was less pronounced when cattle manure was applied. This study shows that the system improves soil water status allowing plants to escape from dry spells. However, at the same time it can lead to loss of nutrients, particularly nitrogen

Leguminosas de habito lianescente: importancia chave para a fixacao biologica de nitrogenio na sucessao secundaria inicial?

Estudo da importancia da fixacao biologica de nitrogenio (FBN) para recuperacao de nitrogenio em sistemas agroflorestais, em Presidente Figueiredo-AM (Brasil)

Effect of planting technique and amendment type on pearl millet yield, nutrient uptake, and water use on degraded land in Niger

Due to increased population pressure and limited availability of fertile land, farmers on desert fringes increasingly rely on marginal land for agricultural production, which they have learned to rehabilitate with different technologies for soils and water conservation. One such method is the indigenous zai technique used in the Sahel. It combines water harvesting and targeted application of organic amendments by the use of small pits dug into the hardened soil. To study the resource use efficiency of this technique, experiments were conducted 1999–2000, on-station at ICRISAT in Niger, and on-farm at two locations on degraded lands. On-station, the effect of application rate of millet straw and cattle manure on millet dry matter production was studied. On-farm, the effects of organic amendment type (millet straw and cattle manure, at the rate of 300 g per plant) and water harvesting (with and without water harvesting) on millet grain yield, dry matter production, and water use were studied. First, the comparison of zai vs. flat planting, both unamended, resulted in a 3- to 4-fold (in one case, even 19- fold) increase in grain yield on-farm in both years, which points to the yield effects of improved water harvesting in the zai alone. Zai improved the water use efficiency by a factor of about 2. The yields increased further with the application of organic amendments. Manure resulted in 2–68 times better grain yields than no amendment and 2–7 times better grain yields than millet straw (higher on the more degraded soils). Millet dry matter produced per unit of manure N or K was higher than that of millet straw, a tendency that was similar for all rates of application. Zai improved nutrient uptake in the range of 43–64% for N, 50–87% for P and 58–66% for K. Zai increased grain yield produced per unit N (8 vs. 5 kg kg-1) and K (10 vs. 6 kg kg-1) compared to flat; so is the effect of cattle manure compared to millet straw (9 vs. 4 kg kg-1, and 14 vs. 3 kg kg-1), respectively, Therefore zai shows a good potential for increasing agronomic efficiency and nutrient use efficiency. Increasing the rate of cattle manure application from 1 to 3 t ha-1 increased the yield by 115% TDM, but increasing the manure application rate further from 3 to 5 t ha-1 only gave an additional 12% yield increase, which shows that optimum application rates are around 3t ha-

Effect of planting technique and amendment type on pearl millet yield, nutrient uptake, and water use on degraded land in Niger

Due to increased population pressure and limited availability of fertile land, farmers on desert fringes increasingly rely on marginal land for agricultural production, which they have learned to rehabilitate with different technologies for soils and water conservation. One such method is the indigenous zai technique used in the Sahel. It combines water harvesting and targeted application of organic amendments by the use of small pits dug into the hardened soil. To study the resource use efficiency of this technique, experiments were conducted 1999–2000, on-station at ICRISAT in Niger, and on-farm at two locations on degraded lands. On-station, the effect of application rate of millet straw and cattle manure on millet dry matter production was studied. On-farm, the effects of organic amendment type (millet straw and cattle manure, at the rate of 300 g per plant) and water harvesting (with and without water harvesting) on millet grain yield, dry matter production, and water use were studied. First, the comparison of zai vs. flat planting, both unamended, resulted in a 3- to 4-fold (in one case, even 19- fold) increase in grain yield on-farm in both years, which points to the yield effects of improved water harvesting in the zai alone. Zai improved the water use efficiency by a factor of about 2. The yields increased further with the application of organic amendments. Manure resulted in 2–68 times better grain yields than no amendment and 2–7 times better grain yields than millet straw (higher on the more degraded soils). Millet dry matter produced per unit of manure N or K was higher than that of millet straw, a tendency that was similar for all rates of application. Zai improved nutrient uptake in the range of 43–64% for N, 50–87% for P and 58–66% for K. Zai increased grain yield produced per unit N (8 vs. 5 kg kg-1) and K (10 vs. 6 kg kg-1) compared to flat; so is the effect of cattle manure compared to millet straw (9 vs. 4 kg kg-1, and 14 vs. 3 kg kg-1), respectively, Therefore zai shows a good potential for increasing agronomic efficiency and nutrient use efficiency. Increasing the rate of cattle manure application from 1 to 3 t ha-1 increased the yield by 115% TDM, but increasing the manure application rate further from 3 to 5 t ha-1 only gave an additional 12% yield increase, which shows that optimum application rates are around 3t ha-