A meta-analysis of intercropping in Africa: impacts on crop yield,farmer income,and integrated pest management effects

Poverty and hunger in Africa are prevalent and will increase in absolute terms with population growth and continued land degradation. Therefore, there is a need for sustainable agricultural strategies, such as conservation agriculture (CA) and integrated pest management (IPM). Among CA practices, intercropping holds the promise of providing benefits to smallholders through increased crop yields and income as well as improved resource use. We review intercropping’s effects on crop yield, income, and output of IPM practices in Africa. On average, intercropping increases crop yields by 23% and gross income by 172 USD/ha, but effects vary significantly depending on management practices and agro-ecological factors. There was no evidence that yields and gross income for intercropping treatments increase when leguminous intercropping combinations, minimum/reduced tillage, pesticides, or fertilizers were utilized. Dual use of herbicides and intercropping practices garnered 1442 USD/ha more in gross income and yielded 1422 kg/ha more compared to those in conventionally managed fields, signifying the positive influence supplemental inputs can have on intercropping’s effects. Although IPM practices increased yields by 20%, on average, IPM systems integrated with intercropping yielded 24% less than IPM systems that did not. This meta-analysis indicates that intercropping is an advantageous sustainable agricultural practice, but that its effective implementation would depend on considering other factors such as adequate control of competing vegetation. There is a clear need for more scientific studies which examine intercropping’s role in complex sustainable agricultural systems, in order to understand its effects in differential environmental and socioeconomic situations and to optimize the practice’s transfer and benefits.     

A Meta‐Analysis on the Elasticity of Demand for Pesticides

There is an increasing policy interest in pesticide taxation schemes as a measure to reduce harmful effects of pesticide use. The effectiveness of such tax depends, however, on the price elasticity of demand for pesticides. Moreover, information on these demand elasticities and their determinants is of crucial relevance for policy‐making and normative modeling approaches. In this article, we present a meta‐analysis based on studies that have estimated pesticide demand elasticities in Europe and North America. Our meta‐analysis reveals that the own‐price elasticities of demand for pesticides are, with a median of ?0.28, significantly smaller than zero, but also significantly larger than ?1, i.e. to be inelastic. We find that the demand for pesticides for special crops is less elastic than that for arable and grassland. In addition, the demand for herbicides is more elastic than for other pesticides. Studies that consider only short‐term horizons and little flexibility for farmers to adjust to price changes generate significantly less elastic pesticide demands. The results also indicate that more recent studies identify lower pesticide price elasticities of demand. Furthermore, we find that peer‐reviewed studies tend to find more inelastic results compared to grey literature.     

Ambiguity,learning opportunities and risk‐neutral regulation

Two current issues in management of public risks, ambiguity and learning, are addressed in the context of managing ecosystems with thresholds, and regulating treatment safety as might apply, for example, to human and animal health, pesticides and herbicides. Reconsidering a recent claim that, in systems that penalise violation of thresholds, learning opportunities induce riskier decision‐making, I find no incentive for ambiguity seeking. But opportunity to benefit from learning may indeed induce riskier decisions, an effect that diminishes and eventually disappears as penalties become larger. A recent claim that a rational regulator of pharmaceutical drugs would be ambiguity preferring – a claim that has obvious applicability to a broader set of treatments – is then examined. Ambiguity‐tolerant patients may indeed prefer a menu of ambiguous treatments and opportunity to learn and switch, rather than a single treatment with known risk. But the source of ambiguity matters. Patient heterogeneity, prior to and independent of policy, generates ambiguity for individuals and motivates preference for a menu of treatments. However, expanding the menu does not justify approving treatments that are generally riskier. Finally, I challenge the perennial claim that the regulator of risks to human health and safety should seek to maximise expected value.     

Factors influencing adoption of conservation tillage in Australian cropping regions*

The purpose of this research is to improve understanding of conservation tillage adoption decisions by identifying key biophysical and socio‐economic factors influencing no‐till adoption by grain growers across four Australian cropping regions. The study is based on interviews with 384 grain growers using a questionnaire aimed at eliciting perceptions relating to a range of possible long‐ and short‐term agronomic interactions associated with the relative economic advantage of shifting to a no‐tillage cropping system. Together with other farm and farmer‐specific variables, a dichotomous logistic regression analysis was used to identify opportunities for research and extension to facilitate more rapid adoption decisions. The broader systems approach to considering conservation tillage adoption identified important determinants of adoption not associated with soil conservation and erosion prevention benefits. Most growers recognised the erosion‐reducing benefits of no‐till but it was not an important factor in explaining whether a grower was an adopter or non‐adopter. Perceptions associated with shorter‐term crop production benefits under no‐till, such as the relative effectiveness of pre‐emergent herbicides and the ability to sow crops earlier on less rainfall were influential. Employment of a consultant and increased attendance of cropping extension activities were strongly associated with no‐till adoption, confirming the information and learning‐intensive nature of adopting no‐till cropping systems.     

Optimal management of annual ryegrass (Lolium rigidum Gaud.) in phase rotations in the Western Australian Wheatbelt*

Lucerne (Medicago sativa L.) helps to prevent soil salinisation in the Western Australian Wheatbelt by reducing recharge to saline water tables. There is broad consensus, though, that it is not sufficiently profitable to motivate producers to plant it at the intensity at which considerable off‐site benefits would be conferred. This paper employs a multiple‐phase optimal control model to explore the value of this perennial pasture for the management of herbicide‐resistant annual ryegrass (Lolium rigidum Gaud.) in a crop–pasture rotation, given the difficulty of observing this value in practice. The availability of selective herbicides for efficient weed control is found to determine whether or not it is profitable to adopt lucerne pasture under optimal management. Herbicide resistance requires producers to employ costly, non‐selective treatments for in‐crop weed control. Thus, it motivates the adoption of perennial pasture in which cost‐effective forms of control can be implemented. Moreover, this result is robust to feasible changes in the current economic environment.     

Yield and income risk-efficiency analysis of alternative systems for rice production in the Guinea Savannah of Northern Ghana

Risk efficiency of rice grain yield and returns to farm operators' household resources generated from an improved short‐duration cover crop fallow system were compared with (traditional) natural bush fallow, and continuous rice‐cropping systems. The improved fallow system involved maintaining Calopogonium mucunoides, seeded into a natural bush fallow for 2 years before planting to rice. With no chemical fertilizer application, which reflects farmers' practice in the area, average grain yield for continuous rice (1,185 kg/ha) and the cropping sequence incorporating a natural bush fallow (1,175 kg/ha) did not differ, but were higher for the improved fallow system (1,304 kg/ha). This suggests that nutrient contribution from the leguminous cover crop made up for critical crop N requirements in the improved fallow. Stochastic dominance of grain yield distributions from the improved fallow system, relative to the other two cropping systems, was more dramatic with no N fertilizer application compared to treatments with 30 kg/ha N. Average returns were highest for the improved fallow system, followed by the natural bush fallow‐cropping system, and then continuous rice, under the no N fertilizer treatment regime. With 30 kg/ha N fertilizer, income risk efficiency was less clear (compared to treatments with no N fertilizer), especially between continuous rice and the improved fallow treatment, because of faster N mineralization effects on continuous rice. In contrast, the improved cover crop fallow system completely dominated the natural bush fallow treatment under both fertilizer regimes. Rice production systems that incorporated the leguminous cover crop fallow were superior to the natural bush fallow system, based on both grain yield and average farm income risk‐efficiency considerations.     

Terms of trade effects on endogenous growth rates in LDCs

Abstract

This paper presents a model in which long‐term GDP growth rates of LDCs are dependent upon world price levels. The model combines an endogenous growth framework a la Romer (1986, Journal of Political Economy, 94, pp. 1002–1037) with traditional Heckscher‐Ohlin‐Samuelson international trade, while assuming investment in capital to be financed solely by domestic savings. This relatively strong assumption is justified by the empirical observation that for most LDCs foreign investment constitutes only a very small part of gross capital formation. We find that an increase in the price of capital‐intensive goods will raise the long‐term growth rate. In other words, in this model protection of the capital‐intensive goods sector will cause higher economic growth.     

Sense and sustainability revisited: the limits of total factor productivity measures of sustainable agricultural systems

Many economists have advocated and applied total social factor productivity (TSFP) (i.e., total factor productivity estimated with both market and non‐market inputs and externalities, and with all factors valued at social prices) as a single all‐embracing measure of agricultural sustainability. This paper reviews the conceptual and practical issues in measuring TSFP and shows that no one measure alone will be theoretically or empirically robust as an indicator of sustainability. TSFP is a conceptually flawed measure since inclusion of non‐market inputs and outputs and social price‐based valuation, in most cases, violates the theoretical basis underlying those estimates. Trends in TSFP also have limited value in diagnosing the nature of sustainability problems, unless changes in productivity are related to underlying changes in technology, human and physical infrastructure, and indicators of resource quality. More attention needs to be given to defining key indicators of agro‐ecosystem health and relating these measures to trends in productivity. This analysis must be sufficiently disaggregated and for a long enough time period to allow for spatial and temporal variability inherent in agricultural production. Secondary data at the district level on both conventional inputs and outputs and resource quality have recently allowed more quantitative estimates of sustainability and its causes. With limited data, yield growth decomposition analysis can often be used to provide valuable insights into sustainability problems. Meanwhile, there is a need to invest in long‐term experimental and panel surveys of farmers and their fields for key production systems in order to provide long‐term data that will allow full productivity accounting, using more formal statistical procedures. Regardless of the approach selected, the findings of this paper strongly suggest a need for economists, agronomists and soil scientists to collaborate in integrating approaches in order to provide more robust and informative measures of sustainability.     

Determinants of herbicide use in rice production in the Philippines

This study identifies farm‐specific and market factors affecting the adoption of herbicides and the level of herbicide use by rice farmers in the Philippines. This requires the application of a modified version of Heckman's two‐step method to estimate a random‐effects double‐hurdle model for unbalanced panel data. The age of the farmer, household size, and irrigation use are significant determinants of the decision of farmers to adopt herbicides as an alternative to manual weeding, while economic variables such as the price of herbicides, total income, and access to credit determine the level of herbicide use. Determinants of both adoption and level are land ownership, farm area, and the method of crop establishment. These results are potentially relevant when designing policies to reduce excessive herbicide use or to encourage the adoption of alternative weed control methods such as integrated weed management.     

A Case Study Approach to Comparing Weed Management Strategies under Alternative Farming Systems in Ontario

When research was initiated into comparing alternative method's of managing weeds in Ontario's major field cash crops, no field trial data existed. Twenty-five farmers were therefore surveyed for their production data on corn, beans and fall-seeded cereal grains, including weed management practices, input costs and wage rates, yields and product prices. Nine farmers were classified "conventional" because of their heavy dependence on synthetic herbicides, which were routinely broadcast on the three focus crops. Nine farmers were classified as "reduced input" if they placed reduce dependence on herbicides for at least one of the focus crops. Seven organic farmers placed zero reliance on herbicides, using instead substitutes such as crop rotations, smother crops, soil tillage and timeliness of field operations. Although organic farmers spent the most time and money on weed control, their overall direct costs of production were lowest for all three focus crops. Crop gross margins were highest on organic farms, partly because of lower production costs, but also because of higher product prices along with comparable crop yields. Linear programming model results for whole-farm analyses revealed highest net farm incomes on organic farms and lowest on conventional farms, in part due to lower overhead costs on organic farms, and in part due to greater enterprise diversification and to greater self-sufficiency in material inputs. These case study results need broader-scale testing to verify the conclusion that organic or reduced-input methods of weed management offer viable alternatives to conventional approaches.     

Extension services,product quality and yields: the case of grapes in Argentina

This article studies the impact of publicly subsidized agricultural extension services on yields and product quality. We use panel data from grape producers in Mendoza, Argentina to estimate the impacts of farmer trainings. We find a negative overall impact on yields and evidence of a positive average impact on the adoption of higher‐quality grape varieties. By analyzing the dynamic pattern of the estimated effects, we find evidence of a temporary decrease in yields suggesting the existence of an adjustment process following the introduction of higher‐quality grapes. The overall negative effect on yield is driven by a sharp drop in the year of participation. This fades after year one, and two to three years after treatment we observe increases in higher‐quality grape production. Findings reinforce the importance of temporal dimension of extension services.     

The impact of commodity price shocks among regional economies of a developing country

Volatile commodity prices have become commonplace in the world economy. Although is widely accepted that commodity‐rich countries are affected by this phenomenon, information about how commodity price shocks impacts their regional economies is scarce. This work analyses how shocks in copper prices impact the economies of the major copper‐producing regions in a developing country, such as Chile. To achieve this goal, a two‐step method is implemented. First, we estimate long‐term copper prices using the Wets and Rios approach (2015) and these estimates are then contrasted with those forecast by the Chilean public advisory committee. Second, a general equilibrium model is implemented to simulate the effects of both expansive and restrictive copper price cycles within major producing regions in Chile. Our results show that the proposed approach yields more homogeneous price projections than those made by the Chilean Government, which, in turn, are very close to variations in response to negative shocks. The price simulations confirm that price cycles affect the savings of government and business, which directly dampens regional production, mainly via investment, capital mobilisation and diversification of production. Because of this, fiscal revenues generated by copper sales act as a trade cycle term multiplier in regional economies. Overall, within copper‐producing regions, we suggest implementing long‐term policies to improve profit distribution efficiency.     

The political ecology of rice intensification in south India: Putting SRI in its places

The system of rice intensification (SRI) has been promoted across Asia as a means to improve rice yields while decreasing water use and external inputs. It is argued to be a generalisable means by which to revalidate smallholder livelihoods and improve food security across the region. Current debates about SRI, however, remain predominantly technical in scope, focusing on field‐level outcomes. To more adequately understand the potential of SRI for smallholder farmers, we argue that it is necessary to situate SRI within a political ecology framework that addresses how the adoption and practice of SRI is shaped by uneven access to key assets including labour, water, and extension networks. Fieldwork conducted in Mahabubnagar district in Telangana, south India—where SRI had been widely disadopted despite the achievement of higher yields—is used to illustrate why agronomic analysis must engage directly with the complex social contexts in which farmers operate.     

Economic analysis of different options in integrated pest and soil fertility management in maize systems of Western Kenya

The major biotic constraints to the production of maize, the major staple food in Western Kenya, are field pests such as Striga and stem borers, and low soil fertility. To counter these constraints, new cropping systems have been developed, including “push‐pull,” rotations with promiscuous soybean varieties and green manure crops, and imidazolinone resistant‐ (IR‐) maize. To analyze the technical and economic performance of these technologies, both with and without fertilizer, on‐farm researcher‐managed long‐term trials were implemented over six seasons in two sites each in Vihiga and Siaya districts of Western Kenya. The economic results, based on marginal analysis using a multioutput, multiperiod model, show that the new cropping systems with fodder intercropping (push‐pull) or soybean rotations were highly profitable. Push‐pull is more profitable but requires a relatively high initial investment cost. Green manure rotation, IR‐maize, and fertilizer all increased yields, but these investments were generally not justified by their increased revenue. We argue that research on rotation and cropping systems to tackle pest and soil fertility problems in Africa deserve more attention. This will require increased collaboration between agronomists and economists to set up long‐term experiments with new cropping systems to develop proper economic models.     

Cropland use,yields, and droughts: spatial data modeling for Burkina Faso and Niger

For countries with recurrent droughts, the design of drought impact mitigation measures could benefit from analyses of determinants of yields and prices of local crops at regional and district level. This study applies dynamic spatial panel data regression models to yields and prices of four major food crops across regions of Burkina Faso and Niger, over sample periods between 1984 and 2006. Results lend support to mainly simultaneous spatial spillovers, particularly for millet and cowpea prices and sorghum yields in Niger, and maize yields in Burkina Faso. After accounting for these effects, most crop yields are found to be weakly price‐responsive, as envisaged by a supply‐side geographical diffusion hypothesis. Seasonal rainfall elasticity estimates suggest that dominant food crops have slight advantage margins in terms of relative resilience to rainfall shortages. However, this result is to be weighed against low millet yields in Niger, and marked drops in sorghum yields during officially declared droughts in Burkina Faso.     

Contracting for Canola in the Great Plains States

Canola has become an important crop in the last decade in the United States. Production of canola is risky and competes with other crops that have varying risk reduction mechanisms. Processors develop and offer contracts with varying specifications that allow growers to reduce risk and attract canola production. In this study, preplant contracting strategies were evaluated in terms of risk and return for growers and processors. Alternative contracts include fixed‐price‐variety‐specific with and without act‐of‐God provisions, and an oil‐premium contract. Grower returns and processor gross margins were simulated and resulting distributions were evaluated using stochastic efficiency with respect to a function. In the dominant growing region, growers would prefer fixed‐price‐variety‐specific contracts versus contracts with oil premiums. The latter would only be preferred by crushers that are highly risk averse. The results vary regionally suggesting that contract types should vary by region to be acceptable to a broader range of growers and processors.     

Higher fuel and food prices: impacts and responses for Mozambique

Rising world prices for fuel and food represent a negative terms‐of‐trade shock for Mozambique. The impacts of these price rises are analyzed using various approaches. Detailed price data show that the world price increases are being transmitted to domestic prices. Short‐run net benefit ratio analysis indicates that urban households and households in the southern region are more vulnerable to food price increases. Rural households, particularly in the North and Center, often benefit from being in a net seller position. Longer‐term analysis using a computable general equilibrium (CGE) model of Mozambique indicates that the fuel price shock dominates rising food prices from both macroeconomic and poverty perspectives. Again, negative impacts are larger in urban areas. The importance of agricultural production response in general and export response in particular is highlighted. Policy analysis reveals difficult trade‐offs between short‐run mitigation and long‐run growth. Improved agricultural productivity has powerful positive impacts, but remains difficult to achieve and may not address the immediate impacts of higher prices.     

Enhancing ecosystem services in vineyards: using cover crops to decrease botrytis bunch rot severity

Botrytis bunch rot is a disease that causes loss of yield and quality in many fruit and vegetable crops in temperate climates worldwide. The rot is caused by the fungus Botrytis cinerea, a saprophytic necrotroph. In grapes, the presence of the fungus can reduce yield, taint wine and increase its sensitivity to oxidation. In the current work, inter-row phacelia and ryegrass were mulched in situ in winter 2005 and compared with a bare ground control. The mulches were applied under 10-year-old Chardonnay vines in a 10-replicate randomized block design in New Zealand. Functional soil biological activity increased by 1.5–4.5 times in the two cover crop treatments compared with the control, an effect related to elevated soil moisture in these treatments. This increase in soil moisture and a higher rate of soil biological activity increased vine debris degradation, reduced B. cinerea primary inoculum on the debris and decreased B. cinerea severity at flowering (December 2005) and harvest (April 2006). These results show the potential of mulched cover crops to enhance soil ecosystem services, reduce variable costs and improve the sustainability of viticulture and potentially other agricultural systems, in temperate climates worldwide.     

Impact of trade liberalisation on dairy market price co‐movements between the EU,Oceania, and the United States

This study investigates the impact of trade liberalisation on the spatial price co‐movements between the dairy markets of the EU, Oceania, and the United States. We consider two main dairy products, namely butter and whole milk powder (WMP), and employ R‐Vines to assess the development of the tail dependence between the price series. We split the time span (i.e. 2000‐2017) in December 2007 to capture the change in the tail dependence as well as in the potential of each region to act as the central market. Our findings indicate that the EU acts as the central market for butter in both sub‐periods, whereas the EU succeeds Oceania in acting as the central market for WMP from the first sub‐period to the next. Further findings highlight slightly increasing tail dependence in the butter market and in the WMP market for the EU‐OCE and EU‐US pairs. However, the tail dependence for the WMP prices between Oceania and the United States weakens, in which we attribute to the 2013 Chinese ban on milk powder imports from Oceania.     

桂西北喀斯特区域土地开发整理模式与持续利用对策研究--以环江毛南族自治县为例

桂西北喀斯特山区自然灾害频繁,水土流失严重,生态环境脆弱,人地矛盾突出,人均耕地不足0．02hm^2,有限的土地承裁着过量的人口。生态环境压力很大,但尚有一定数量的土地后备资源;土地资源总量较大,类型多样,具有多宜性,开发条件优越,但土壤质量不高。空间分布地域分异明显;以环江县为例,分析了区域土地资源个性特征,指出了现阶段喀斯特区域土地资源开发整理主要可行的小流域治理模式、农牧复合模式、生态家庭农场模式、立体生态农业模式、异地安置模式;提出了依托规划强化管理、建立产业化机制、生态环境影响评价制度和建立生态重建协调机制等土地资源可持续利用的对策。