Carbon sequestration in dryland ecosystems of West Asia and North Africa

The West Asia–North Africa (WANA) region has a land area of 1.7 billion ha, and a population of 600 million. Desertification and soil degradation are severe problems in the region. The problem of drought stress is exacerbated by low and erratic rainfall and soils of limited available water holding capacity and soil organic carbon (SOC) content of less than 0.5 per cent. The SOC pool of most soils has been depleted by soil degradation and widespread use of subsistence and exploitative farming systems. The historic loss of a SOC pool for the soils of the WANA region may be 6–12 Pg compared with the global loss of 66–90 Pg. Assuming that 60 per cent of the historic loss can be resequestered, the total soil‐C sink capacity of the WANA region may be 3–7 Pg. This potential may be realized through adoption of measures to control desertification, restore degraded soils and ecosystems, and improve soil and crop management techniques that can enhance the SOC pool and improve soil quality. The strategies of soil‐C sequestration include integrated nutrient management (INM) and recycling, controlled grazing, and growing improved fodder species on rangeland. Improved technologies for cropland include use of INM and biofertilizers, appropriate tillage methods and residue management techniques, crop rotations and cover crops, and water and nutrient recycling technologies. Through adoption of such measures, the potential of soil‐C sequestration in the WANA region is 0.2–0.4 Pg C yr⁻¹. Copyright © 2002 John Wiley & Sons, Ltd.     

Soil erosion on Alfisols in Western Nigeria: II. Effects of mulch rates

The effects of four rates of straw mulching on runoff and soil loss were compared with those of no-tillage treatments under natural rainfall conditions using field runoff plots of 25 × 4 m established at 1, 5, 10 and 15% slopes on the International Institute of Tropical Agriculture (IITA) research site near Ibadan, Nigeria. The four rates of straw mulching were 0, 2, 4 and 6 t/ha. The mean annual runoff was 50, 10, 4 and 2% of the total annual rainfall for mulch rates of 0, 2, 4 and 6 t/ha, respectively. Runoff from unmulched treatments was not related to slope. Runoff loss from no-till treatments was only 2% of the rain received. The mean soil losses for the rainstorms greater than 25 mm were 143, 16, 2 and 0.4 kg/ha per mm of rain received for mulched rates of 0, 2, 4 and 6 t/ha, respectively. The soil loss declined exponentially with increasing mulch rate with exponents ranging from approximately ?0.3 to ?0.7. The soil losses from the no-till plots were equal to those from plots that received mulch at the rate of 6 t/ha. Soil erodibility was significantly influenced by time after clearing, with maximum K reached two to three years after forest removal. The nutrient loss in runoff and eroded soil was significant only for unmulched treatments. The maximum annual loss of NO₃-N in runoff was about 15 kg/ha. The maximum annual loss of total N in eroded soil from unmulched plots was about 180 kg/ha, that of P, 5 kg/ha, and that of K, about 14 kg/ha.     

Soil erosion on Alfisols in Western Nigeria: IV. Nutrient element losses in runoff and eroded sediments

Nutrient element losses in runoff and eroded sediments were monitored during 1972 on different slopes and under different soil and crop management treatments. The experiments were conducted on 25 × 4 m field runoff plots, established on natural slopes of 1, 5, 10 and 15%. The soil and crop management treatments consisted of bare fallow (plowed), maize-maize (plowed and mulched), maize-maize (plowed), maize-cowpeas (no-till), and cowpeas-maize (plowed).Total loss of nutrient elements in runoff and eroded soil materials was significantly affected by slope and by soil and crop management treatments. Total annual nutrient element losses in runoff were 55 kg/ha for bare-fallow, 17 kg/ha for maize-maize (plowed), 12 kg/ha for cowpeas-maize (plowed), 2.3 kg/ha for maize-maize (plowed and mulched) and 4.3 kg/ha for maize-cowpeas (no-till). The concentration of nitrate in seepage water was two or three times higher than in surface water. Nutrient losses in eroded soil materials from the mulched and no-till treatments were negligible. From the plowed treatments, greatest losses were of organic matter and total nitrogen. The enrichment ratios were 2.4 times for organic carbon, 1.6 times for N, and 5.8 times for available phosphorus.     

Water management in various crop production systems related to soil tillage

Soil tillage, of different types and intensity and performed at different antecedent soil moisture conditions, is an important tool for agricultural water management. Tillage systems have important applications for increasing irrigation efficiency, enhancing the effectiveness of drainage systems, improving water quality, decreasing runoff losses and minimizing soil erosion, increasing runoff losses for water harvesting and supplemental irrigation, and decreasing percolation losses and creating aquatic environments for rice cultivation. The versatility and diversity of applications of tillage systems depend on the choice of tillage techniques. No-tillage methods with residue mulches are useful to conserve soil water. Chisel tillage and subsoiling methods along with ridge-tillage techniques are useful in increasing irrigation efficiency. No-tillage systems are useful in decreasing sediment density and transport of sediment laden pollutants in runoff, and puddling and wet tillage techniques or soil compaction are used in rice cultivation. Finally soil compaction and techniques to increase water repellence are useful for water harvesting for subsequent use in supplemental irrigation.     

Land configuration and soil nutrient management options for sustainable crop production on Alfisols and Vertisols of southern peninsular India

Land configuration in combination with nutrient management has the potential to improve the productivity of Alfisols and Vertisols in the semi-arid tropics. A four year (1989–1990 and 1992–1993) field experiment was conducted at Coimbatore, India on Alfisols (Chromic Cambisol) to compare the effect of land configuration and nutrient management practices on yield of rainfed sorghum (Sorghum bicolor (L.) Moench). The land configuration treatments were flat bed (FB, the traditional practice), open ridging (OR, ridges, 45 cm apart and 30 cm high) and tied ridging (TR, same as OR plus ridges were tied randomly). The manure and fertilisers were farm yard manure (FYM, livestock excreta plus litter at 5 Mg ha⁻¹) and coir dust (CD, by-product after the extraction of coir from the coconut (Cocos nucifera L.) husk at 12.5 Mg ha⁻¹) in combination with nitrogen (N) and phosphorus (P) fertiliser levels. Tied ridges stored 14% more soil water and produced 14% and 11% more grain and straw yields of sorghum, respectively, than did flat bed. However, crop yield in TR was comparable with OR. Application of CD at 12.5 Mg ha⁻¹ combined with 40 kg N ha⁻¹ and 9 kg P ha⁻¹ was beneficial for more soil water storage and increased yield of sorghum by 7% over FYM at 5 Mg ha⁻¹ + 40 kg N ha⁻¹ and 9 kg P ha⁻¹. In Vertisols (Vertic Cambisols), experiments were conducted for two years (1991–1992 and 1992–1993) to evaluate land configuration practices. The treatments were broad bed furrow (BBF, 120 cm wide bed with 30 cm wide and 15 cm deep furrows on both sides), compartmental bunding (CB, bunds of 15 cm height formed in all the four sides to form a check basin of 6 m × 5 m size), ridging (RD, ridges were formed for each and every row of the crop manually at four weeks after sowing) and FB under sorghum + pigeonpea (Cajanus cajan (L.) Millsp) and pearl millet (Pennisetum glacum (L.) Stuntz) + cowpea (Vigna unguiculata (L.) Walp) intercropping separately. Compartmental bunding stored 22% more soil moisture and increased the yield of sorghum + pigeonpea intercropping than did FB in a low rainfall year. In a high rainfall year, BBF produced 34% and 33% more grain yield of sorghum and pearl millet base crops, respectively, over FB. However, BBF and CB were comparable. Pigeonpea intercrop under sorghum followed the same trend as its base crop, whereas, yield of cowpea differed compared to the pearl millet base crop. Tied ridging and application of manures (CD or FYM) in combination with inorganic N and P fertiliser can increase the soil water storage and yield of crops compared to traditional flat bed cultivation in rainfed Alfisol and related soils of semi-arid tropics. Similarly BBF and CB land configuration practices could be adopted on Vertisols for better water conservation to increase the soil fertility and productivity of intercropping systems.