Leaf area index (LAI) is a key variable for the understanding of several eco-physiological processes within a vegetation canopy. The LAI could thus provide vital information for the management of the environment and agricultural practices when estimated continuously over time and space thanks to remote sensing sensors.This study proposed a method to estimate LAI spatial and temporal variation based on multi-temporal remote sensing observations processed using a simple semi-mechanistic canopy structure dynamic model (CSDM) coupled with a radiative transfer model (RTM). The CSDM described the temporal evolution of the LAI as function of the accumulated daily air temperature as measured from classical ground meteorological stations.The retrieval performances were evaluated for two different data sets: first, a data set simulated by the RTM but taking into account realistic measurement conditions and uncertainties resulting from different error sources; second, an experimental data set acquired over maize crops the Blue Earth City area (USA) in 1998. Results showed that the proposed approach improved significantly the retrieval performances for LAI mainly by smoothing the residual errors associated to each individual observation. In addition it provides a way to describe in a continuous manner the LAI time course from a limited number of observations during the growth cycle. 相似文献
Aflatoxin level in 300 farmers’ stores in four agro-ecological zones in Benin, a west African coastal country, were determined over a period of 2 years. At sampling a questionnaire was used to evaluate maize storage practices. Farmers were asked what storage structure they used, their storage form, storage period, pest problems in storage and what was done against them. Beninese farmers often changed their storage structures during the storage period, transfering the maize from a drying or temporary store to a more durable one. Most of the farmers complained about insects damaging stored maize. Often, storage or cotton insecticides were utilized against these pests. Regression analysis identified those factors that were associated with increased or reduced aflatoxin.
Maize samples in the southern Guinea and Sudan savannas were associated with higher aflatoxin levels and the forest/savanna mosaic was related to lower toxin levels. Factors associated with higher aflatoxin were: storage for 3–5 months, insect damage and use of Khaya senegalensis-bark or other local plants as storage protectants. Depending on the agroecological zone, storage structures that had a higher risk of aflatoxin development were the “Ago”, the “Secco”, the “Zingo” or storing under or on top of the roof of the house. Lower aflatoxin levels were related to the use of storage or cotton insecticides, mechanical means or smoke to protect against pests or cleaning of stores before loading them with the new harvest. Fewer aflatoxins were found when maize was stored in the “Ago” made from bamboo or when bags were used as secondary storage containers. 相似文献
The long isolation of Albania and the scarcity of raw materials has traditionally led to the production of bread from crops other than wheat, like maize, which is the basic ingredient for maize bread (bukë misri), rye, which is used to prepare rye bread (bukë thekre), and chick-pea, used in chick-pea bread (bukë me qiqre). Today, these traditional breads are accompanied by other types, such as brown bread from soft wheat (bukë zize). In the present work, the traditional Albanian breads were characterised in order to assess their quality. The results obtained indicated that the protein content reflected the characteristics of the raw material used, being higher in the chick-pea bread and in bread made from high extraction rate wheat flour, while both fat and yellow pigment levels were higher in maize bread. A high humidity value was found in many of the breads examined, especially in maize bread, with consequent risks of moulds and a shortened shelf-life. 相似文献
Laboratory tests were carried out to examine the insecticidal effect of three commercially available diatomaceous earth (DE) formulations on wheat and maize against three major stored-grain beetle species: Rhyzopertha dominica, Sitophilus oryzae, and Tribolium confusum. The three DEs tested were Insecto®, PyriSec®, and Protect-It®. These DEs were applied alone or in all possible combinations (Insecto®+PyriSec®, Insecto®+Protect-It®, PyriSec®+Protect-It®, and all three DEs together), at three (total) dose rates: 0.25, 0.5, and 0.75 g/kg of each commodity. Adults of the above species were exposed to the treated commodities for 7 d at 26 °C, and 65% r.h., and after this interval the mortality was measured. For each species, adult mortality was significantly affected by the type of DE, the commodity, and the dose rate. All DEs were less effective against T. confusum, where mortality did not exceed 67%, in comparison with the other two species, where 100% mortality was achieved in some combinations. For all species tested, all DEs were more effective on wheat than on maize. Generally, the mix of two or three DEs was more effective than the application of one DE, for all species and commodities. The results of the present work clearly indicate that a blending of several DEs together may produce a new DE formulation that is highly effective at low dose rates. 相似文献
Tortillas were prepared using commercial hydrocolloids, stored for 7 and 14 days and their available, resistant and retrograded resistant starches, were evaluated alongside their in vitro starch digestibility. Available starch (AS) decreased with storage time and tortillas with hydrocolloids had lower values than the control sample. Tortillas elaborated with TC-20 gum did not present substantial differences in AS. Control tortilla had resistant starch (RS) content that increased with storage time but, in general, tortillas with hydrocolloids did not show any change in RS values with storage time, except tortillas with TC-1 gum that presented a slight increase after 7 storage days. Approximately 50% of RS is due to the retrogradation phenomenon as it was shown by the amount of retrograded resistant starch (RRS). Tortillas with added hydrocolloids had lower hydrolysis percentage and the hydrolysis was slower than in the control. In general, tortillas prepared with hydrocolloids had a lower tendency for retrogradation than control tortillas; it is important to consider this to obtain tortillas with better texture and lower RS content. 相似文献
Whole maize plants at the milk and dough maturation stages were ensiled in August and October 1984, for periods of 45 and 40 days, respectively. Thirteen net bags containing herbage samples were buried at different locations within the silo to determine changes and losses during the conservation period. Thermocouple wires and small-diameter plastic pipes were connected to every bag for temperature and gas measurements. Air penetration in the upper layer was much faster than in the inner parts. Losses in dry matter of 3.9-7.4% were found in well sealed sites in the bunkers, and of up to 36% at locations where air penetrated. The rate of air penetration into the silage and temperature at various sites in the bunker were recorded. Correlation between CO2, and N2, contents in the silage was very high (r2 = 0.995) whereas oxygen levels were close to zero. 相似文献
Maize was stored for 2 months in chambers maintained at 25 °C to simulate conditions observed in the central part of the “Corn Belt” of the United States when the grain warms because of high summertime temperatures after a period of winter storage. Maize was brought to three moisture contents (m.c.) within the range typically observed in farm and commercial storage, and was inoculated to simulate the amount of storage mold contamination typical of this situation. Certain of the experimental units were packed in insulation so that heat could accumulate within the grain masses to simulate hot spots. The wettest grain heated rapidly and became semi-anaerobic. The hot grain then dried rapidly, with the amount of moisture loss influenced by the ratio of water vapor pressures inside and outside the grain. The hot grain cooled and became more aerobic over time. New infections by storage molds, disappearance of viable field molds, development of kernel damage, and changes in atmospheric gases within the grain masses were correlated with the grain moisture or temperature and the rate at which the moisture and temperature changed. The rate of increase in new kernel damage was as high as 3.3% per week. Both the rate of respiration and the estimated ratio of starch to fat consumed were associated with the mean grain m.c. during the trial, and the estimated ratio of starch to fat consumed was in the range of 2.2/1–2.6/1 in the grain containing 16.6–18.2% m.c. That both fat and starch were consumed calls into question loss estimates based on starch metabolism alone. The fat content of the grain decreased more than 10% in some experimental units, but increased less than 5% in others. The protein content generally increased as other grain constituents were consumed. 相似文献