RELATIVE VARIABILITY IN WHEAT YIELDS ACROSS COUNTRIES AND OVER TIME

Wheat yield variability is analysed in light of recent concern that rapid technological change has caused increased instability in world cereal production. The coefficient of variation of wheat yields is estimated for 57 countries from detrended data for various periods between 1951 and 1986. The coefficient of variation in wheat yields is shown to be determined by country size, moisture regime and temperature. Technological variables, such as level of adoption of high-yielding varieties and fertiliser dose, had no effect on differences in yield variability across countries. Analysis of yield variability for the same set of countries for three periods from 1951 to 1986 shows a general decline in yield variability since 1975 in developing countries. Analysis of wheat yield variability in India at the state and district levels confirms the analysis of country level data. The coefficient of variability of wheat yields in India in the period 1976-85 has fallen to less than half the level in the 1950s and this decline is statistically significant.     

SOURCES OF INCREASED VARIABILITY IN WORLD CEREAL PRODUCTION SINCE THE 1960s

Recent growth in world cereal production has been accompanied by a more than proportional increase in the standard deviation of production. This study applies variance decomposition procedures to data on crop production by major geographical regions of the world to analyse the sources of this increased instability. It is found that the increase in aggregate production variability is predominantly due to increased yield variability and to a simultaneous loss in offsetting patterns of variation in yields between crops and regions. These changes are probably associated with the sharp increase in the variability of world cereal and oil prices since the early 1970s and with the more widespread adoption of improved seed/fertiliser intensive technologies.     

Producer Experience, Learning by Doing, and Yield Performance

Current crop insurance rating procedures consider only performance for the individual crop in question. Recent farm legislation has given producers considerable planting flexibility and, as a result, many have shifted to new crops. Producers without a production history for the new crop may be offered levels of insurance that do not accurately reflect their expected yields. Likewise, premium rates may not reflect a producer's actual risk for a new crop. We examine the extent to which information about expected yields may be gleaned from a consideration of historical performance on other crops. We also consider the extent to which yield performance exhibits learning by doing such that yields improve with experience. Though the results are mixed, we generally find that yield performance tends to improve with experience. However, when yields are conditioned on historical yield performance for other crops, the importance of experience is diminished significantly. Yield performance is related to a number of farm characteristics. Finally, we examine the extent to which yield variability is correlated across crops for individual farmers. Implications for crop insurance rating practices are discussed. The results demonstrate robust correlation between a farm's historical yield on other crops and a newly produced crop—a factor largely ignored in current crop insurance contracts.     

No-till technology: benefits to farmers and the environment? Theoretical analysis and application to Finnish agriculture

We assess theoretically and empirically the private profitabilityand social desirability of conventional tillage and no-tillwhen crop yields, production costs and nutrient and herbiciderunoff damages are taken into account. Based on Finnish experimentaldata, no-till provides higher social and private profit thanconventional tillage for barley but not for oats and wheat,for which the production cost advantage of no-till does notcompensate for lower yields in the private optimum. As regardssocial returns, no-till provides slightly better overall environmentalperformance but, given the existing valuation of nutrient andherbicide runoff damage, this is not enough to give no-tillan advantage in oats and wheat cultivation. Thus, the key factorsdetermining the private and social profitability of no-tilland conventional tillage are yields and production costs ratherthan environmental performance.     

Seasonal variability,land values and willingness–to–pay for a forward wheat contract with protein premiums and discounts

This article investigates the impact of a protein premiums and discounts system on the income stream from growing wheat. Based on a biological relationship between protein and yield in uncertain seasonal conditions, it shows that such a system reduces the expected level and variability of wheat income. It is subsequently argued, using a numerical analysis, that protein payments affect both the attraction to wheat growers of forward contracts and the value of land used for wheat. The nature of both of these impacts is related to the level of seasonal variability affecting the land. Consequently, wheat growers in the more unreliable regions of the wheatbelt may have been particularly disadvantaged by the system.     

Modeling skewness with the linear stochastic plateau model to determine optimal nitrogen rates

Accurate modeling of skewness is needed to increase the actuarial fairness of crop insurance. We test Day's conjecture that crop yield skewness becomes negative as nitrogen rates increase and determine how well a linear response stochastic plateau (LRSP) production function matches the pattern of observed skewness using four long‐term nitrogen experiments. Stillwater wheat is consistent with Day's conjecture, but the skewness for Lahoma and Altus wheat yields as well as Altus cotton yields are not. The LRSP assumes normal random effects and can explain only a small part of observed skewness, so a new LRSP with skew‐normal random effects is introduced, which comes closer to explaining the observed skewness and should increase the accuracy of nitrogen rate recommendations. Negative skewness reduced optimal nitrogen rates and positive skewness increased optimal nitrogen rates.     

Integrating crop modelling and production economics to investigate multiple nutrient deficiencies and yield gaps

A method is described for integrating crop modelling and production economics to quantify optimum applications of multiple nutrients and yield gaps. The method is demonstrated for crop production in the high‐rainfall zone of southern Australia. Data from a biophysical crop model were used to overcome the persistent problem of inadequate experimental data. The Mitscherlich function was expanded to accommodate four variable inputs – nitrogen, phosphorus, potassium and sulphur – and the expansion path was used to determine the economic optimum application of all four nutrients. Modelling revealed the state‐contingent yield potential and the extent to which unrealised yield could be explained by profit‐maximising behaviour and risk‐aversion by growers. If growers and their advisors were guided by the methods described, they would be better equipped to assess crop nutrient demands and limitations, predict yield potential, additional profit and the risks associated with high input systems in a variable climate. If scientists were more aware of the extra profits and the risks involved (as well as the quantitative relationships between inputs and outputs) when thinking about what to produce and how to do so, they would be more circumspect about the net benefits to be obtained from closing yield gaps.     

TREATMENT OF RISK IN A CROP PROTECTION INFORMATION SYSTEM

The importance of risk in a farm-level management information system designed to help farmers make spraying decisions relating to leaf rust of barley is examined. Using utility functions which were elicited for a small number of cereal growers, and probability distributions of yield losses generated using the information system, it was found that strategy assessment using the criterion of maximisation of expected monetary value or the criterion of maximisation of expected utility could be expected to lead to identical recommendations in most years, for a wide range of risk attitudes.     

Is research on marginal lands catching up? The case of unfavourable wheat growing environments⋆

It is widely believed that the Green Revolution had very little effect in unfavourable or marginal environments. Many researchers have been concerned about the slow progress of technical change in marginal environments and the level of research resources allocated to these areas. This paper provides empirical evidence that there has been significant growth in wheat yield potential in marginal environments, especially during the post‐Green Revolution. International yield trial data, covering all major wheat growing environments from 1964 to 1999, were used in estimating the growth in wheat yield potential and changes in yield variability. The global database on wheat varietal adoption and yield gains based on estimated wheat yield growth rates were used to determine production increases due to wheat breeding research. Results show greater progress in shifting the wheat yield frontier in marginal areas, particularly in drought and high temperature environments. Furthermore, yield variability in marginal environments has notably declined, while it has increased slightly in favourable environments. While initial gains came from crossover of varieties from favourable environments, targeted breeding efforts have contributed significantly to more recent productivity growth in marginal environments. Increased production from marginal environments accounted for around 25% of the total wheat production increase in 1997. These findings show greater progress in wheat research and the huge potential of improving wheat productivity in unfavourable environments.     

The Impact of Biofuel Policies on Crop Acreages in Germany and France

A major concern about biofuels is that increasing biofuel feedstock demand reduces availability of crops for food and feed leading to higher food prices. This paper investigates relations between biofuel policies and prices of rapeseed, the major feedstock used for biodiesel production in Europe, and the impact of rapeseed prices on crop acreages in Germany and France. Biodiesel is an important biofuel in Europe, and Germany and France are the largest biodiesel producers in Europe. First, the various biofuel policies in Germany and France are discussed, followed by an analysis of their effects on rapeseed prices. Although theory indicates that such effects exist, we could not find empirical evidence for them. Second, using regional land use panel data from Germany and France we investigate empirically whether crop shares have been affected by rapeseed prices in the period 2000–2015 and whether these price effects changed because of biofuel policy changes. Results show that wheat shares in Germany and France did respond to rapeseed prices, but barley shares did not. Moreover, mandatory blending introduced in Germany in 2007 and production quotas introduced in France in 2005 led to a stronger effect of rapeseed prices on wheat shares, but again did not affect barley shares.     

Effect of changes in population density and crop productivity on farm households in Malawi

This study examines the ex‐ante farm‐household effects of changes in family size, yield potential, and yield gaps using a farm‐household simulation model that reflects the economic and biophysical conditions of central Malawi. Disparities between growth in human population and crop yields present challenges for farm‐household crop production and income in sub‐Saharan Africa. We focus on the effect of growth in yield potential and a more efficient use of livestock manure as approaches to improving crop production and incomes in the face of looming population pressures. Our results suggest that, even without considering climate change, expected changes in population density and crop prices in 2050 mean that per person crop production and income may fall by 21% compared to 2013 values if yield potential and yield gaps remain constant. However, per person crop production and income could increase in 2050 by 8% compared to 2013 values if (1) growth rates of yield potential rise for maize by 1.13% each year and for legumes rise by at least 0.4% each year, and (2) farmers use livestock manure more efficiently. Our foresight approach to considering crop production at the farm‐household scale supplements macro‐scale analyses of the production dimension of food security.     

Revealing the determinants of wheat yields in the Siberian breadbasket of Russia with Bayesian networks

Higher crop yields are critical to satisfy the rising global food demand. Russia holds untapped potential for increasing agricultural production because current grain yields are often far below the potentially attainable yields. Western Siberia is an important breadbasket in Russia, where wheat yields fall particularly short of their potential. Our goal was to assess the determinants of yield variations among farmers in the province of Altai Krai in Western Siberia. We conducted 67 structured in-person interviews with corporate farm managers and individual farmers about the potential determinants of wheat yields and complemented these data with 149 additional observations obtained from the provincial agricultural extension service. We used Bayesian networks (BNs) to represent the relationships between the explanatory parameters and contemporary wheat yields and to examine qualitative future scenarios of future yields. The results revealed higher yields on larger farms than on medium and small farms. Our results corroborated that the application of fertilizers and herbicides and the implementation of new equipment had large positive impacts on the yields. The scenario of higher future production costs and lower precipitation resulted in a yield reduction from 7.6 dt/ha to 5.3. Overall, our results suggest that policies aimed at increasing wheat yields should concentrate on the education of farmers and encourage higher input applications, particularly for small-scale farms. Additionally, policies should address concurrent challenges, such as a higher drought frequency, through the application of new equipment, seed material and tillage practices.     

Geography of crop yield skewness

Analysis of crop yield distributions provides insights into better understanding how natural resources shape agricultural productivity. This study seeks to provide a rigorous theoretical and empirical understanding of the effects of exogenous geographic and climatic factors on the first three moments of crop yields with focus on the third moment. We hypothesize that exogenous factors having beneficial effects on crop production should make crop yield distributions less positively or more negatively skewed. We employ a large crop insurance data set for corn, soybean, and wheat to find general support for our natural‐resources‐determines‐skewness hypothesis. The proposed statistical method optimally uses correlations between the first three moments. It significantly improves estimation performance over existing methods, including the linear moment model which has been commonly applied in the literature.     

自然降雨与旱地谷子单产水平关系研究——以武安市为例

谷子抗旱性强,水分利用效率高,是我国北方干旱半干旱雨养旱作区的主要杂粮作物。文章主要研究干旱雨养旱作区降雨量对谷子单产的变化规律,从而为提高谷子降水利用效率以及实际生产提供理论依据。基于武安市1983~2012年期间30年的降雨数据和谷子单产数据,研究自然降雨与谷子单产水平关系。采用散点图、建立线性方程、线性回归显著性分析等研究方法,通过统计、对比描述等方式进行分析。结果显示:武安近30年的自然降雨量与谷子的单产之间具有正相关关系,且谷子7、8月份降雨量对其单产具有显著性影响。主要结论:谷子的单产随着降雨量的增加而增加,但不是无限增加,而是有一个最佳降雨临界点490mm;当降雨量在490mm以内变化时,谷子单产随着降雨量的增加呈现增长的趋势;当降雨量超过490mm时,谷子的单产与降雨量负相关;谷子的单产受7月和8月的降雨量影响显著,且2个月降雨量之和占全生育期的63.1%时,谷子的单产较高。     

全球变化背景下气候变暖对中国农业生产的影响

全球变化背景下,气候变暖势必对我国农业生产要素、生产环境、农业生产活动及粮食安全产生重大影响。文章采用文献综述与比较研究的方法,系统分析气候变化对我国光资源、温度、水环境和土壤环境等农业生产要素的影响特征及变化趋势,探讨气候变化对我国作物种植区域和种植制度、农作物病虫害、农业生产能力、农业经济与管理等农业生产活动以及农田生态系统过程、农业生态环境(水环境、土壤环境、耕作环境)的实际影响。在此基础上,明确了我国农业在应对气候变化过程中所面临的主要问题:极端气候事件发生频率加大,自然灾害、气象灾害的风险提高,农业生产的波动性增强;农业病虫害的为害时间延长、危害程度加剧、为害范围增大;农业生态环境日趋恶化,农田土壤的干旱化、盐渍化程度加剧,农业生产能力下降;应对气候变化的农业发展策略及其关键技术亟需解决。     

The rise and fall of public sector plant breeding in the United Kingdom: a causal chain model of basic and applied research and diffusion

This paper examines the barley and wheat breeding programmes of the Plant Breeding Institute (PBI), which was the most successful public plant breeding institute in the UK, until privatization in 1987. The PBI's shares in barley and wheat seed sales are explained, showing that the success with barley was largely a matter of serendipity, whereas the wheat programme followed a more normal pattern. For wheat, the causal chain, or recursive, model decomposes the well-documented link between research expenditures and increases in agricultural productivity into three stages. These are the effects of R&D expenditures on basic research output, measured by publications, the effect of publications and applied R&D expenditures on trial plot yields, and the diffusion of the trial plot technologies, which raises yields on farms. Applying the model to the FBI's wheat varieties allows estimation of the lag structures. In contrast to the results for aggregate agricultural research, for a single plant breeding programme alone there is a considerable lead time before there is any response, followed by a lag distribution only a few years long. The returns to the R&D investments are calculated from the causal chain model, from single equation estimates and by evaluating the yield advantage of the PBI varieties. All three approaches give consistent results, which show that the returns to barley and wheat alone were sufficient to support the entire PBI budget and still give rates of return to applied research of between 14 and 25%. The return to the basic science expenditures of the John Innes Institute has a lower bound of 17%, but must have been even higher than for the PBI if the other Institutes were taken into account. The paper concludes by commenting on the effects of the privatization of the PBI.     

UNDERWRITING ASSISTANCE TO THE AUSTRALIAN WHEAT INDUSTRY — AN APPLICATION OF OPTION PRICING THEORY

For the ten crop seasons 1979-80 to 1988-89, returns to producers in the Australian wheat industry were underwritten by a government-guaranteed price floor. Similar schemes operate in other rural industries (dairy, apples and pears, dried fruits). Although the underwriting provisions have only been triggered once (in the 1986-87 season), the provision of this scheme has acted to reduce the risk normally associated with returns to producers of wheat in all years of its operation. This reduction in risk has been granted free-of-charge by the Commonwealth Government. The guaranteed price can be viewed as a put option taken out by the Government on behalf of growers — it gives growers the option to sell to the Australian Wheat Board at this floor price. The aim of this paper is to apply to this underwriting arrangement the Black-Scholes formula for valuing options, in order to estimate the cost that growers would otherwise have had to pay to obtain cover (through put options) equivalent to the guaranteed price. We also estimate the magnitude of this form of assistance to the industry, which (until now) has not been taken into account unless the returns to growers fell below the guaranteed price.     

Fungicide use under risk in Swiss wheat production

The short-run effects of fungicide application on economic risk and the effects of risk on fungicide use in Swiss wheat production are empirically explored. A quadratic production function model is developed. With the help of the moment-based approach, marginal contributions of fungicides (representing controlled inputs) and of rain (representing uncontrolled inputs) to the variances of yield and revenue are analyzed. It is not possible to show risk-reducing effects of fungicides on yield or revenue. At low rain quantities during the vegetation period fungicides have a statistically significant risk-increasing effect on revenue. Increasing risk leads Swiss wheat growers to use more fungicide. This increase is statistically significant at higher levels of revenue. For example, when risk is doubled fungicide inputs are raised by 44% at the highest revenue quartile.     

PREMIUM RATEMAKING IN AN ALL RISK CROP INSURANCE PROGRAM1

Fluctuation in farm incomes resulting from variation in crop yield is one of the most significant features in agriculture. Crop insurance is a feasible method by which the farmer can protect his income and his investment from the disastrous effects of crop losses due to natural hazards. This study has attempted to cover two parts. First, it has examined the most important-factors influencing crop yields in connection with the premium rate scheme (i.e. the long-run average yield and the level of coverage). These factors include resource inputs, technology, weather, and stochastic variable. Second, it has developed a refined method of approximating the premium rate. The data used in testing normality were based on the Manitoba Crop Insurance Corporation's annual yield survey covering the years 1916 to 1964. The test shows that none of the annual yield distributions within the area surveyed was normally distributed, revealing that a cartful and exact delineation of a crop risk area is necessary. The findings also show that the cyclical pattern of weather and the upward trend in crop production due to technology were evidently important for the adjustment of the level of coverage and premium rate over time. Additional research relating the effects of weather and technology on crop yields would help to establish a more realistic insurance program. Other aspects should not be overlooked. These include (a) other possible levels besides the existing level of coverage and (b) a livestock or a combined crop-livestock insurance program along with the crop insurance program. The purpose of these additional aspects is to provide farmers with a fuller measure of protection.     

Assessing effects of federal crop insurance supply on acreage and yield of specialty crops

Crop insurance may affect harvested acreage and yield by influencing producers’ behavior such as land allocation and input use. Although specialty crops are a major source of farm income, especially on the U.S. west coast, they have not received as much attention as field crops in previous empirical studies. This paper assesses the effect of moral hazard and adverse selection associated with the federal crop insurance program (FCIP) on the acreage and yield of major specialty crops in California. An econometric method that expands the switching regression model is developed to assess the effect. Results suggest that federal crop insurance can change specialty crop growers’ production responses to climate and soil conditions. The moral hazard effect tends to increase the acreage and yield of the specialty crops, whereas the adverse selection effect tends to have the opposite effect. The overall effect of the FCIP on acreage and yield of specialty crops is found to be moderate.