With increased emphasis on risk management in agriculture and a lack of disaggregated or farm-level yield time series, decision makers are often faced with having to make adjustments to temporal yield risk measures obtained from readily available but aggregated yield data. This paper provides some empirical evidence on what type of aggregation bias to expect when measuring temporal yield risk using yield observations averaged across a region relative to yield risk estimated from quarter-section yield time series in wheat. This study highlights some of the challenges faced when estimating aggregation distortions in measuring yield risk defined by temporal variance, especially given the nature of the empirical data set used. Cluster analysis, visual examination of relative frequency distributions and mapping of yield risk clusters suggest that using a readily available, aggregate temporal yield risk measure has the tendency to underestimate yield risk observed at the quarter-section level and that clear, geographic yield risk boundaries do not exist in municipalities or across larger areas in this study. Further research on crops more risky than wheat appears promising.Avec un plus grand inte'ret sur la gestion du risk dans 1 'agriculture et un manque de donne'es de'taillees OM bien de collections de se'ries temporelles sur les rendements, les de'cideurs sont souvent tenus d'apporter des correct$ aux measures du risk obtenues a partir des donne'es de rendements qui sont disponibles. Cet artcle apporte une preuve empirique du type de biais lie a l'agre'gation qui peut &re prsent dans le calcul du risk de rendement temporel obtenu a partir de rendements moyens de ble' observis au niveau regional en comparaison du risk de rendement qui est estime' a partir de donnies base'es sur des quart-de-sections.Cette e'tude met en exergue quelques uns des obstacles qui se pre'sentent dans l'estimation de distosions lie'es a 1 'aggre'gation dans le calcul du risk de rendement ddfini par la variance temporelle, speciallement itant donne la charactkre empirique des donne'es utiliskes. L'analyse de groupe, l'examen visual de la distribution des fre'quences relatives, et la cartographie de classes de risk de rendement sugg2rent que l'utilisation de la measure du risk de rendement base'e sur des donne'es disponibles de risk aggr2ge temporel a tendence a sousestimer le risk de rendement observe au niveau des quart-desections et qu'il n'y a pas de fronti2res de risk de rendement certaines, ge'ographiques qui existent entre les municipalite's OM bien a travers les zones plus larges examine'es dans cette etude.
"A researcher interested in crop yield risk analysis often has to contend with a lack of field- or farm-level data. While spatially aggregated yield data are often readily available from various agencies, aggregation distortions for farm-level analysis may exist. This paper addresses how much aggregation distortion might be expected and whether findings are robust across wheat, canola and flax grown in two central Canadian production regions, differing mainly by rainfall, frost-free growing days and soil type. Using Manitoba Crop Insurance Corporation data from 1980 to 1990, this research, regardless of crop or region analyzed, indicates that (i) spatial patterns in risk are absent; (ii) use of aggregate data overwhelmingly under-estimates field-level yield risk; and (iii) use of a relative risk measure compared to an absolute risk measure leads to slightly less aggregation distortion. Analysts interested in conducting farm-level analysis using aggregate data are offered a range of adjustment factors to adjust for potential bias." Copyright 2005 Canadian Agricultural Economics Society.
Legumes have been shown to increase production in cool‐season grass pastures. However, they are included in relatively few acres of pasture. A split plot experiment with six replications was conducted to evaluate the impact of pasture renovation and grazing management on forage production and species composition of cool‐season grass pastures. Grazing management main plots were grazed to leave low (2‐4 in.), medium (4‐6 in.), or high (6‐8 in.) residue levels. Main plots were intensively grazed (SO 000‐70 000 lb of cows per acre) five or six times per grazing season by lactating Holstein cows. Subplot pasture renovation treatments were (i) an untreated check, or sprayed with glyphosate and interseeded with (ii) alfalfa (Medicago sativa L.), (iii) red clover (Trifolium pratense L.) and birdsfoot trefoil (Lotus corniculatus L.), or (iv) “graziers mix” (a mixture of legumes and grasses). Areas that were grazed to leave low residue level produced less forage mass (4.7 ton/acre) than areas grazed to medium (5.4 ton/acre) or high (5.5 ton/acre) residue levels. When averaged across years and grazing management treatments, renovated areas produced 1.8 ton/acre (46%) more forage than the control. Of interseeded species, alfalfa, red clover, and orchardgrass persisted through the study (more than 25% of the dry matter in at least one of the pasture renovation treatments). By June 1998, thistle (Carduus and Cirsium spp.) was present in all treatments. Fewer thistle was present in areas that were grazed to leave low residue (10 sq yd) than high residue (18 sq yd) and in renovated areas (9 sq yd) than the control (22 sq yd). The additional forage produced as a result of pasture renovation cost from S8.07/ton to $12.81/ton. This study indicates that pasture renovation can be a valuable tool for increasing forage production in cool‐season grass pastures. Problem and Literature Summary Cool‐season grass pastures in the North Central Region often do not produce to their potential. Renovation of pastures with legumes and productive grasses can increase pasture productivity. The addition of legumes to pastures provides N, increases forage quality and intake of forage, and increases summer growth. In spite of all the potential benefits from legumes, they are included in relatively few acres of pasture. The inclusion of adapted cool‐season grasses can also increase pasture productivity. One of the challenges in maintaining renovated pastures is grazing management. This experiment addressed two pasture renovation issues: (i) does residue height left after grazing impact forage production and/or the persistence of desirable species, and (ii) identification of species which are adapted, productive, and have relatively good persistence under grazing in the north central region. Study Description In June of 1994 a split plot experiment with six replications was planted in an old bromegrass pasture. From 1995 through 1997 the area was grazed with 50 000 to 70 000 lb of lactating Holstein cows per acre five or six times per approximate 5‐mo g...
1979;and Burns and Chamblee, 2000a) and Midwest (Wedin et al., 1967;Gerrish et al., 1994;and Riesterer Increasing costs associated with winter feeding have renewed inter- et al., 2000) regions of the USA. The applicability of this est in extending the grazing season in the North-Central USA. A factorial design with three N treatments was applied to existing smooth practice and more specifically the stockpiling of smooth bromegrass (Bromus inermis Leyss.) pastures to evaluate initiation dates bromegrass (Bromus inermis Leyss.) in the North-Cenand N fertilization rates for stockpiling forage. Stockpile initiation tral USA have not been thoroughly evaluated. Smooth bromegrass is the predominant cool-season Nitrogen fertilization treatments were 0, 56, or 112 kg ha Ϫ1 . Data grass in much of the North-Central USA. Widespread collected included forage mass in October, residual forage mass the adaptation (Vogel et al., 1996), winterhardiness (Limin subsequent April, leaf concentration, and forage nutritive value. Octoand Fowler, 1987), and high palatability make smooth ber forage availability was generally greater from earlier stockpile bromegrass a well-adapted forage crop for hay or pasture initiation dates (2.58, 2.44, 1.98, 1.28, 0.78, and 0.65 Mg dry matter ha Ϫ1 in this region. Smooth bromegrass produces the majority for stockpile initiation dates, respectively; LSD at 0.05 ϭ 0.19). Leaf mass available of its growth in early spring (Engel et al., 1987; Moore in October was similar through the 15 July stockpile initiation date. et al., 1991). Relatively slow regrowth after defoliation October forage mass was greater with 56 kg N ha Ϫ1 than with 0 N ferand summer growth rate raises questions regarding the tilization, averaging 1.26, 1.75, and 1.85 Mg ha Ϫ1 (LSD at 0.05 ϭ 0.14) suitability of smooth bromegrass for stockpiling (Carlfor 0, 56, and 112 kg N ha Ϫ1 , respectively, when averaged across stockson and Newell, 1983). In a multilocation trial in Wisconpile initiation dates and years. Trends in April forage mass for stocksin, Riesterer et al. (2000) evaluated seven cool-season pile initiation date and N fertilization tended to be similar to October. grasses under varying levels of fertility and determined Crude protein tended to increase and acid detergent fiber and neutral that smooth bromegrass stockpiled beginning in early detergent fiber tended to decrease as stockpile initiation was later in the season. These results indicate that initiating stockpiling of smooth August produced inadequate forage dry matter (DM) bromegrass-dominated pastures about 1 July with 56 kg N ha Ϫ1 optito be considered suitable for stockpiling in the Upper mizes stockpiled smooth bromegrass in the North-Central region.
A set of crop alternatives ranging from traditional, low risk to less common and/or high risk crops is ranked according to their impact on overall risk using two measures. These two measures would aid cropping decisions by providing (1) a priori guidance on overall risk impact, and (2) a means to reduce the need for complex E‐V frontier estimation. Results suggest the number of crops that may depend on the riskiness of crop alternatives form which a producer chooses. Some reductions in necessary calculations for E ‐V analysis are therefore suggested.
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