Rainfall concentration for increasing corn production under semiarid climate

The ridge and furrow farming of rainfall concentration (RC) system is being promoted to increase water availability to crops for improving and stabilizing agricultural production in the semiarid Loess region of northwest China. In the system, plastic-covered ridges serve as rainfall harvesting zones and furrows serve as planting zones. In recent years, however, the current RC practices are still confined to rural family units for very limited supplemental irrigation purposes. To adopt this system for large-scale use in the semiarid region and bring it into full play, it is necessary to test the befitting rainfall range for RC farming. A field study (using corn as an indicator crop) combined with rainfall simulation was designed to determine the effects of RC practices on soil water content, crop yield and water use efficiency (WUE) under three rainfall levels (230 mm, 340 mm and 440 mm) during the growing seasons of 2006 and 2007. The results indicated that with the rainfalls ranging within 230-440 mm, RC system can increase soil water content in 0-100 cm and temperature conditions in the topsoil (0-10 cm) in furrows by 5-12% and 0.7-1 °C, respectively. The corn seedlings emerged 1-2 days earlier, the developmental stages generally occurred earlier, and the plant height and total dry matter all significantly increased (P < 0.05). In 2006, compared to conventional flat (CF) practice, the grain yield and WUE in the RC system increased by 75.4% and 73.3%, respectively at 230 mm rainfall, and by 36.7% and 40.2%, respectively at 340 mm rainfall, but there was no significant difference between the RC₄₄₀ and CF₄₄₀ patterns. In 2007, the grain yield and WUE were 82.8% and 77.4%, respectively higher in the RC₂₃₀ plots than in the CF₂₃₀ plots, 43.4% and 43.1%, respectively higher in the RC₃₄₀ plots than in the CF₃₄₀ plots, and 11.2% and 9.5%, respectively higher in the RC₄₄₀ plots than in the CF₄₄₀ plots. Combining yield and WUE, it could be concluded that the optimal rainfall upper limit for RC system is below 440 mm rainfall in the experiment. In the case of corn, the adoption of RC practice in the 230-440-mm rainfall area will make the system more attractive during the whole growth period and offer a sound opportunity for sustainable farming under semiarid climate.     

The effect of simulated runoff on the erosion of gypsiferous soils

The effect of runoff generation on the erosion of gypsiferous soils under different experimental conditions was investigated by applying simulated rainfalls of 48 and 58 mm h⁻¹ to experimental plots exhibiting representative characteristics of these soils. The 45 experiments indicate differing erosive behaviour as test conditions varied. Suspended gypsum yields ranged from 0-3.9 gm⁻² h⁻¹ the higher values occurring with the steeper slopes and dry soil conditions. The differences among the soils tested were mainly due to variations in underlying rock outcrop, whilst within each soil type, slope was the most important variable. Transport of suspended gypsum by runoff is inversely related to rock outcrop, and positively related to slope. The highest erosion rates are registered in Gypsic Calcisols, followed by Gypsic Calcisols (lithic phase), while production of suspended gypsum is not verified for Dystric Leptosols. By transporting gypsum particles down-slope, runoff is probably responsible for the dynamic evolution of gypsiferous hillslopes as well as the genetic evolution of the studied soils.     

半干旱盐渍化地区果园土壤盐分离子相关性研究

以甘肃省秦安县兴国镇郑川村果园土壤为研究对象,利用统计分析的方法对500个土样盐分离子含量的相关性进行了研究.结果表明:该研究区土壤阴离子主要是HCO3-、SO42-,阳离子主要是Na+.CO32- 与HCO3-、Mg2+ 之间存在着显著的负相关,与Na+ 之间存在着极显著的正相关;HCO3- 与Cl- 之间存在着极显著的负相关,与Mg2+ 之间存在着极显著的正相关;Cl- 与SO42-、Ca2+、Mg2+、Na+ 之间存在着显著的正相关,其中与Ca2+、Na+ 之间存在着极显著的正相关;SO42- 与Ca2+、Mg2+、Na+ 之间存在着极显著的正相关;Ca2+ 与K+ 之间存在着极显著的正相关,与Na+ 之间存在着显著的负相关;Mg2+ 与K+ 之间存在着显著的负相关;K+ 与Na+ 之间存在着极显著的负相关.通过对盐分离子的聚类分析发现,Cl-、Mg2+、CO32-、Ca2+、K+ 和HCO3- 在该区土壤中有着相似或相近的运移特征.对相关分析和偏相关分析这两种分析方法所得结果进行了对比分析,它们之间存在着明显的差异,偏相关分析能进一步消除由于其他变量的影响,因而能够更加准确地刻化多元变量其中的两个变量之间的相关性.     

Microbiological activity in a soil 15 years after its devegetation

The effect of devegetation on the microbiological and biochemical quality of a soil in a semiarid climate was studied 15 years later. In this climate, devegetated soils do not generate spontaneous vegetation and this leads to diminished carbon fractions. Microbial activity as determined by parameters of general microbial activity, such as basal respiration and ATP, confirms the negative effect of devegetation on the microbiological quality of the soil. This negative effect also is reflected in microbial biomass C, which acts as an indicator of microbial population size. Specific parameters, such as oxidoreductase enzymatic activities (dehydrogenase), or hydrolases of the N cycle (protease that hydrolyses N-α benzoyl-L-argininamide), also point to the negative effect of devegetation on soil biochemical quality. All this was in evidence despite the fact that 15 years had passed since devegetation.     

Climate and groundwater effects on the establishment, growth and death of Prosopis caldenia trees in the Pampas (Argentina)

Semiarid woodlands dominated by Prosopis caldenia thrive at the dry edge of the Argentinean Pampas. Deforestation and increased precipitation have driven sustained water table level rise in the region that are likely to affect the dynamics of remnant woody vegetation patches. Here we analyze the effect of climate and groundwater level on the establishment, growth and death of P. caldenia located on lowland (current water table <0.5 m deep) and upland (current water table 8 m deep) positions within rolling sandy landscape. Standard dendrochronological techniques were applied on 98 cross sections and cores of P. caldenia trees. Results allowed us to estimated that trees in the lowland established a few years earlier than in the upland (1929 vs. 1936) and died between 1991 and 2002, while trees in higher positions are still alive. As a result of a faster growth in the lowland, maximum mean basal area increment took place earlier (1950s vs. 1990s) and achieved a higher mean value than in the upland (41.63 vs. 37.41 mm²). While mean annual chronologies were not associated across stands, an opposite highly significant association was found for the mean growth trends suggesting long-term effects of water table depths on growth. We found a different association between mean annual growth and climate, with lowland trees showing a negative response to precipitation before and during the growing season, and upland trees displaying a positive response to summer rainfall inputs. Temperature at the end of the growing season had a positive effect in the lowland whereas temperature during the growing season had a positive effect in the upland. These results show how groundwater can induce diverging sensitivity of forest growth and survival to climate variability, enhancing growth at optimum depths (2-8 m in our study) but depressing it or even killing trees when it approaches the surface (<2 m in our study). Groundwater dynamic should be considered in forest management and conservation strategies in semiarid woodlands in Central Argentina.     

Are drought and wildfires turning Mediterranean cork oak forests into persistent shrublands?

In the Iberian Peninsula Mediterranean oak forests have been transformed into a mosaic landscape of four main patch-types: forests, savannas, shrublands and grasslands. We used aerial photographs over a period of 45 years (1958–2002) to quantify the persistence and rates of transitions between vegetation patch-types in southern Portugal, where cork oak is the dominant tree species. We used logistic regression to relate vegetation changes with topographical features and wildfire history. Over the 45 years, shrublands have been the most persistent patch-type (59%), and have been expanding; forests are also persistent (55%) but have been decreasing since 1985; savannas and grasslands were less persistent (33% and 15%, respectively). Shrublands persistence was significantly correlated with wildfire occurrence, particularly on southern exposures after 1995. In contrast, forest persistence decreased with wildfire occurrence, and forests were more likely to change into shrublands where wildfire had occurred after 1995.     

Impacts of elemental S applied under various temperature and moisture regimes on pH and available P in acidic, neutral and alkaline soils

We evaluated the effect of elemental S (S⁰) under three moisture (40, 60, 120% water-filled pore space; WFPS) and three temperature regimes (12, 24, 36°C) on changes in pH and available P (0.5 N NaHCO₃-extractable P) concentrations in acidic (pH 4.9), neutral (pH 7.1) and alkaline (pH 10.2) soils. Repacked soil cores were incubated for 0, 14, 28 and 42 days. Application of S⁰ did not alter the trends of pH in acidic and neutral soils at all moisture regimes but promoted a decrease in the pH of alkaline soil under aerobic conditions (40%, 60% WFPS). Moisture and temperature had profound effects on the available P concentrations in all three soils, accumulation of available P being greatest under flooded conditions (120% WFPS) at 36°C. Application of S⁰ in acidic, neutral and alkaline soils resulted in the net accumulation of 16.5, 14.5 and 13 g P g^–1 soil after 42 days at 60% WFPS, but had no effect under flooded conditions. The greatest available P accumulations in the respective soils were 19, 19.5 and 20 g P g^–1 soil (equivalent to 38, 41, 45 kg P ha^–1) with the combined effects of 36°C, 60% WFPS and applied S⁰. The results of our study revealed that oxidation of S⁰ lowered the pH of alkaline soil (r=–0.88, P<0.01), which in turn enhanced available P concentrations. Also, considering the significant relationship between the release of sulphate and accumulation of P, even in acidic soil (r=0.92, P<0.01) and neutral soil (r=0.85, P<0.01) where the decrease in pH was smaller, it is possible that the stimulatory effect of sulphate on the availability of P was due to its concurrent desorption from the colloidal surface, release from fixation sites and/or mineralization of organic P. Thus, in the humid tropics and irrigated subtropics where high moisture and temperature regimes are prevalent, the application of S⁰ could be beneficial not only in alleviating S deficiency in soils but also for enhancing the availability of P in arable soils, irrespective of their initial pH.     

Econometric analysis of the determinants of adoption of rainwater harvesting and supplementary irrigation technology (RHSIT) in the semiarid Loess Plateau of China

Using a binary logistic regression model, this paper evaluates the determinants of farmers’ decisions to adopt rainwater harvesting and supplementary irrigation technology (RHSIT) and its elasticity of adoption in the rain-fed farming systems, based on a survey of 218 farmers in the semiarid areas of Loess Plateau in 2005. The results indicate that 12 variables are significant in explaining farmers’ adoption decisions. Farmers’ educational background, active labor force size, contact with extension, participation in the Grain-for-Green project, and positive attitudes towards RHSIT are some of the variables that have significantly positive effects on adoption of RHSIT, while farmer's age and distance from water storage tanks to farmers’ dwellings have significantly negative correlation with adoption. The probability of adoption also increases with increased targeting of institutional variables: credit obtained, assistance obtained, and technical training received. Farmers in villages that have more erosion problems are more likely to adopt RHSIT. Besides, the model indicates that a 1 unit increase in the diversity of irrigated crops grown by a household, especially high-value crops, results in a 6.98 times increase in the probability of RHSIT adoption. Variables such as family size, off-farm activity, level of family income, risk preference, and land tenure do not significantly influence adoption. This information will help prioritize the factors that affect adoption decisions and provide insight on pathways to increase the adoption of RHSIT.     

覆膜对半干旱区谷子生长发育·产量及水分利用效率的影响

[目的]筛选出半干旱区谷子（Italian millet）覆膜种植最佳模式.[方法]供试谷子品种为晋谷43号.共设4个处理和1个对照（CK）,分别为：T1全膜覆盖平作穴播（使用1.2m膜）,T2全膜覆盖垄沟种植,T3膜侧沟播（0.4 m膜）,T4起垄不覆膜,T5露地条播（CK）.[结果]谷子覆膜栽培比露地早熟,其中全膜覆盖垄沟种植谷子产量最高为10 335.15 kg/hm2,比CK增产35.00％,水分利用效率为22.68 kg/（mm·hm2）,比CK增加41.75％.全膜覆盖垄沟种植较其他处理明显提高集雨效果和保墒,有利于提高谷子水分利用效率及产量.[结论]该研究可为半干旱地区谷子地膜覆盖种植提供理论依据.     

Slow progress with integrated rural development programmes in Kenya's arid and semiarid lands

Integrated rural development programmes (IRDPs) in Kenya's Arid and Semiarid Lands (ASAL) arose out of a recognition that they had been neglected in the past and that levels of poverty, the need to increase production and the threat of environmental degradation merited special attention. The primary goal of the IRDP activities was to increase agricultural productivity, thereby contributing to food self-sufficiency. This goal was reflected in the heavy concentration of resources in natural resource development. Such concentration was frequently at the cost of the development of human resources. Similarly, investment in physical infrastructure and in small-scale industry was neglected. It was expected that IRDPs would be planned and implemented at the District-level and would assist in the establishment of district administrative capacity. Participatory planning at the local level was considered a prerequisite to effective and sustainable integrated development. Sadly, IRDPs have been largely unsuccessful in both primary goals. While the reasons for failure are complex, it appears that two key issues stand out: (a) assumptions about the ability of government agricultural services to develop the potential of the ASAL were unrealistic, and (b) there was a lack of real devolution of power to district administrations, and more noticeably, to subdistrict levels. Despite the difficulties, the attraction of IRDPs to the ASAL remain strong. In a time of declining government budgets, they provide a means of getting funds to the district-level and of catering for the special problems of semiarid environments. The continuing justification for IRDPs may be summarized as follows: (a) there is still a real problem of feeding a growing population in ASAL districts and in high agricultural potential zones; (b) without IRDPs in ASAL districts, standards of living would certainly fall; (c) this may prompt out-migration from ASAL areas into high potential zones; (d) such out-migration would occur in the context of increasing land pressure and rising unemployment in high-potential areas; (e) IRDPs, by sustaining populations within ASAL districts, could contribute to food security in high-potential areas; (f) IRDPs might also contribute to food security in ASAL districts themselves, by strengthening traditional production systems in these areas. The primary goal is to sustain the populations in ASAL districts by improving their food security. Although natural resource management is still necessary, there must be increasing attention paid to human resource development. Only then can a true transfer of power take place to ASAL districts, whereby their people effectively participate in overcoming and managing local problems.