首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
《Field Crops Research》1998,57(2):153-162
Cane and sugar yields within a sugar mill region can vary with geographical location, harvest date, harvest age, variety and crop class. It is not possible, due to limited mill capacity, to harvest all cane when maximum yields are attained. Given a prolonged harvest season, an important question is how the harvest of individual paddocks of cane should be scheduled so as to maximise net revenue for the entire mill region. This paper presents the application of an optimisation model to the Mossman mill region with the objectives of maximising sugar yield and net revenue in relation to harvest date and crop age. Six years of block productivity data classified according to district, crop class, variety, harvest date, harvest age, cane yield and sugar yield, were used to generate the input parameters for the model. Other inputs were sugar price, growing and milling costs, and transport and crushing capacity. With current crushing capacity and harvest season lengths, an application of the model to maximise sugar yield showed a 4% increase in sugar yield compared to current practice, but a 23% decrease in net revenue due to a shorter crop cycle with less ratoons before replanting. Optimising with respect to net revenue, gave a 3% gain in sugar yield with an 8% gain in net revenue. When crushing capacity was allowed to increase for current season lengths, the model showed a 14% gain in net revenue given fixed milling costs. It is concluded that there is scope for optimising harvest date to improve profitability in this mill region given current harvest season lengths and land area.  相似文献   

2.
Sugarcane crops are managed over 8 million hectares in Brazil and future extensions might occur on less favorable lands where irrigation would be necessary to increase and stabilize yields. Root growth was studied by sequential soil coring under rainfed and irrigated conditions for one cultivar widely planted in Brazil. Root length densities (RLD) were measured 34, 49, 125, 179, 241 and 322 days after planting (DAP) down to a depth of 1 m. At the harvest (332 DAP), root intersects (a proxy for RLD) were counted on two vertical trench walls in each water supply regime, down to a depth of 6.0 m. The highest RLD in deep layers (below a depth of 0.6 m) were observed in the rainfed crop from 125 DAP onwards. By contrast, the highest RLD in the upper layers during dry periods were found in the irrigated crop. The maximum depth reached by roots at the harvest was little affected by irrigation: 4.70 m and 4.25 m in the rainfed and irrigated crop, respectively. About 50% of root intersects were observed below the depth of 1 m in the two water supply regimes. This pattern suggested a strong genetic control of root growth in deep soil layers. The total amount of root intersects 332 DAP was 49% higher in the rainfed crop than in the irrigated crop, and root distribution was more homogeneous. Mean root front velocity was about 0.5 cm day−1 the first 4 months after planting and increased thereafter up to the end of the harvest (1.86 cm day−1 and 1.75 cm day−1 on average in the rainfed and the irrigated crops, respectively). Our study pointed out the necessity to take into account the development of sugarcane roots in deep soil layers to improve our understanding of net primary production control by water availability.  相似文献   

3.
Evaluating decision rules for dryland rotation crop selection   总被引：1，自引：0，他引：1  
No-till dryland winter wheat (Triticum aestivum L.)-fallow systems in the central Great Plains have more water available for crop production than the traditional conventionally tilled winter wheat-fallow systems because of greater precipitation storage efficiency. That additional water is used most efficiently when a crop is present to transpire the water, and crop yields respond positively to increases in available soil water. The objective of this study was to evaluate yield, water use efficiency (WUE), precipitation use efficiency (PUE), and net returns of cropping systems where crop choice was based on established crop responses to water use while incorporating a grass/broadleaf rotation. Available soil water at planting was measured at several decision points each year and combined with three levels of expected growing season precipitation (70, 100, 130% of average) to provide input data for water use/yield production functions for seven grain crops and three forage crops. The predicted yields from those production functions were compared against established yield thresholds for each crop, and crops were retained for further consideration if the threshold yield was exceeded. Crop choice was then narrowed by following a rule which rotated summer crops (crops planted in the spring with most of their growth occurring during summer months) with winter crops (crops planted in the fall with most of their growth occurring during the next spring) and also rotating grasses with broadleaf crops. Yields, WUE, PUE, value-basis precipitation use efficiency ($PUE), gross receipts, and net returns from the four opportunity cropping (OC) selection schemes were compared with the same quantities from four set rotations [wheat-fallow (conventional till), (WF (CT)); wheat-fallow (no-till), (WF (NT)); wheat–corn (Zea mays L.)-fallow (no-till), (WCF); wheat–millet (Panicum miliaceum L.) (no-till), (WM)]. Water use efficiency was greater for three of the OC selection schemes than for any of the four set rotations. Precipitation was used more efficiently using two of the OC selection schemes than using any of the four set rotations. Of the four OC cropping decision methods, net returns were greatest for the method that assumed average growing season precipitation and allowed selection from all possible crop choices. The net returns from this system were not different from net returns from WF (CT) and WF (NT). Cropping frequency can be effectively increased in dryland cropping systems by use of crop selection rules based on water use/yield production functions, measured available soil water, and expected precipitation.  相似文献   

4.
The Korean 2008 self-sufficiency rate for grain was only 26.2%. Because of this, the quantity virtual water (VW) for crop product imports is much greater than that of other countries. International VW trade is especially important to Korea due to its dependency on foreign imports to maintain food security and to establish an agricultural water resource policy. Using international crop products trade statistics during 2003?C2007, this study analyzed the virtual water content (VWC) and international virtual water flow (VWF) of major crops. The national water savings and global water savings were also estimated. Major grain products, including 28 products made from 13 crops, were selected for the analysis, based on the net import and export of products totaling more than 10,000 tons. VWCs were computed for the selected major crop products using the VWC of the primary crop of Korea. International VWFs were estimated using the VWC of each crop products. The amount of imported VW was 16,804 and 226?M?m3 was exported, so that the net imported VW was 16,578?M?m3. VW import is concentrated in wheat, rice, maize (corn), and soybean crops. A small number of countries, including the USA, China, Brazil, etc., account for over 96% of the imported VW, indicating Korea??s heavy dependence on these countries. The average national water savings for Korea and the average global water savings according to crop were estimated using VW flow from international crop products trade during 2003?C2007. The estimate of national water savings was 23,870.3?M?m3. Three major crops, namely wheat, maize and soybean, account for 95.3% of this total VW saving. Global water savings from the VW trade amounted to 7,253.0?M?m3. Korea depends heavily on VW imports concentrated in specific crops and which are primarily imported from a particular set of countries. This indicates that Korea is vulnerable to disruptions in the international grain harvest such as those caused by natural disasters such as floods and drought. Any such disruption could easily become a critical issue for governmental planners who establish food and water supply policies for Korea.  相似文献   

5.
Potato cropping systems in Maine include both continuous potatoes and short-term potato rotations with small grains. Producers recognize the benefits of increased rotations, but the economics of producing a high-valued crop such as potatoes (Solanm tuberosum L.) create incentives for continuous potato production. Research at the USDA-ARS research site in Newport, ME, is evaluating the agronomic and economic impacts of five crops in two-year rotations on potato production and whole-farm profitability. The rotation crops are barley (Hordeum vulgare L.), sweet corn (Zea mays L.) green bean (Phaseolus vulgares L.), soybean (Glycine max L., Mer.), and canola (Brassica napus L.). Enterprise budgets for the five crops were developed. The budgets and historical prices and yields were used as inputs to a Monte Carlo simulation. The simulation was conducted to determine the impact of rotation crops on whole-farm profitability and income risk, as measured by income variability. The net incomes of the five rotation sequences were compared against continuous potatoes. Two rotation crops, sweet corn and green beans, resulted in an increase in net income relative to continuous potatoes. AU of the rotation crops were found to greatly reduce income risk and chance of economic losses. In the case of green beans and sweet corn, the analysis was rerun using data from the research trials on the following potato crop yields. Depending on whether the rotation effect was negative or positive, net income either fell or rose when compared to fist analysis. However, even when the rotation crop led to decreased yields in the following potato crop, income variability and likelihood of economic loss was still superior to the continuous potato rotation. These findings provide support for including rotation crops as a method to improve potato production and sustainability, increase wholefarm profitability, and reduce income risk.  相似文献   

6.
Increased land degradation and shortage of forage resources for animal production over-winter have accentuated the need for alternative cropping systems in northeast China. While short frost-free period and cool temperatures are major limitations to cereal grain production in the northern regions of China (45°N, 122°E), crop varieties that are able to produce food and feed in short growing season and tolerant to low temperature may extend the total cropping period. Three hulless oat (Avena sativa L.) lines, Baiyan 9015, Baiyan 9017 and Baiyan 9044, were bred and tested for 3 years (2004–2006) to determine their suitability for summer seeding in a double cropping system. The new lines were sown both in the spring and summer to provide growers with opportunities to harvest two grain-crops in a year. Averaged across 3 years, Baiyan 9044 produced 2.5 and 1.6 Mg ha−1 yr−1 grain yield when sown in spring and summer, respectively. The new lines seeded in 20th or 21st July and harvested in early October allowed utilization of an average of over 1500 growing degree days (GDDs). For grain yield alone, the net income for two oat crops a year was up to 1390 Chinese yuan (RMB) ha−1, more than that of growing a single oat crop in 3 years, or in most cases, equivalent to monocultured corn (Zea mays L.) production, the dominant crop in the region. In addition, an average of 5 Mg ha−1 of oat straw was produced as valuable forage fodder for the livestock industry, which was in great demand for over-wintering animals. Furthermore, in the traditional single small grain cereal cropping system, bare ground after harvest leads to severe water and wind erosions. Our results indicate that the new oat lines could be a potential crop for summer seeding, particularly when spring-seeded crops fail due to abiotic (hail, drought, etc.) or biotic (e.g. insects) stresses. The double cropping system provides growers with a potential opportunity to facilitate the farming strategy of food, cash crops and control soil erosion in the region.  相似文献   

7.
Nitrogen (N) fertilization of sugarcane crops is a common practice used to reach sustainable levels of productivity, both for plant cane and especially for the ratoon. However, when evaluating the amount of N in the plant derived from fertilizer (NDDF) at harvest, this contribution is approximately 20% of total plant biomass N, which raises questions regarding the efficiency of N fertilization. The goal of this study was to evaluate the N derived from fertilizer (NDFF) during the sugarcane crop development, for both plant cane and first ratoon crop cycles. Two field experiments were performed in São Paulo State, Brazil, in Arenic Kandiustults and in Typic Eutrustox. The sugarcane was mechanically harvested without burning. N fertilizer for both the plant cane (doses of 40, 80 and 120 kg ha−1 of N as urea) and the first ratoon (doses of 50 and 100 kg ha−1 of N as ammonium sulfate) was labeled 15N. The results showed that NDFF contributed up to 40% of the total N in the plant cane at initial stages of development. The magnitude of this contribution decreased during stages of maturity to approximately 10% of total N at harvest. In the first ratoon, application of N fertilizer was more effective for crop nutrition, constituting up to 70% of total N in initial stages of development and decreasing through the cycle, reaching approximately 30% at harvest. Therefore, studies that evaluate NDDF only at harvest can lead to underestimating the role of N fertilizer for sugarcane nutrition. The higher NDFF in ratoon explains why this crop cycle presents a more consistent response to N fertilization than plant cane, as observed in several studies developed under Brazilian conditions in the last decades.  相似文献   

8.
Crop growth is driven by the capture and utilisation of solar radiation. The most productive crop sequences are those that maximise the interception and use of solar radiation. However, there are yield trade-offs because of the timing of transitions between successive crops. A longer duration of one crop will mean that the following crop is sown later and will therefore produce a lower yield. Maximising the yield of a sequence involves a compromise between the yields of successive crops. We describe a case study of a forage cropping rotation in New Zealand, demonstrating how simulation models can be used to define the best compromise between the yields of successive crops, and thereby maximise the total yield of the full sequence.A case study using a series of long-term simulation experiments for four diverse environments in New Zealand was undertaken in a continuous, summer maize - winter cereal, cropping sequence. Maize sowing dates and hybrid durations, and cereal sowing and harvest times were varied systematically. The actual simulated crop and sequence yields varied from site to site, but there was a consistent trend identifying the most productive combinations of sowing date and hybrid duration. The sequence of comparatively late sowing date of maize (1 December) and a long-season hybrid maximised the total yield of the sequence. The highest sequence yields were achieved by balancing the need to capture a high level of annual solar radiation and the need to have a large proportion of solar radiation captured by maize, which has the greater RUE in summer. This analysis illustrates how crop simulation models can be used to design and understand the processes that give the most productive cropping sequences.  相似文献   

9.
《Field Crops Research》2003,83(1):91-100
An attempt is made to quantify the long-term benefit from the sustained production of sugarcane in South Africa using nematicides to reduce the damage caused by nematodes in each crop. The study was conducted using data from the plant crop and four or five ratoon crops from two trials located on similar sandy soils. Treatments comprised aldicarb and an untreated control, applied to a total of 10 sugarcane cultivars. Two cultivars were common to both sites. The plant parasitic nematode communities were similar at both sites except that Meloidogyne javanica was absent from one site. Yield of ratoon crops was correlated with the yield of the plant crop. Annual losses from nematodes were similar over successive crops. Data from both sites showed there to be a significant, positive correlation between yield of the nematicide treated plots and size of the response to treatment. Over a 4-year period, M. javanica alone was responsible for 30% of the losses, equivalent to 15 t cane/ha per year. The long-term effect of nematodes on sugarcane production was measured after calculating a logarithmic function from the observed yields of successive ratoons. Without a nematicide the time taken for the yield to decline to a threshold of 40 t cane/ha per year ranged from a minimum of 1 year in the M. javanica infested site to a maximum of 9 years in the other site. Treatment with a nematicide increased this period considerably. On the site with M. javanica it took a projected 20 years before the yield of one of the cultivars reached the threshold and 43 years for the same cultivar at the other site. The use of a nematicide increased long-term production, on average, by a factor of 3 at the M. javanica infested site and a factor of 5 at the other site. Differences between cultivars in the rate at which ratoon yields declined meant that, over time, the best cultivars at both sites were not the ones which gave the greatest annual yields during the first few crops after planting.  相似文献   

10.
《Field Crops Research》1996,49(1):39-50
Sugarcane was grown under full irrigation in Australia, South Africa and Hawaii. N fertiliser was supplied at a high rate and was non-limiting to biomass accumulation in all but one dataset, where zero and high nitrogen (N) supply regimes were imposed. Crops were sampled for biomass, sucrose, glucose and fructose content of stalks. In one study, the biomass and sugar content of all green crop components were also determined. The objective was to compare the accumulation of reducing sugars, glucose and fructose, with sucrose, and how this responds to agronomic manipulations of crop duration, cultivar and nitrogen supply. Such knowledge can be used to assess the scope for maximising, by agronomic or genetic means, the partitioning of biomass to the economic product, sucrose and maximising the purity of juice for efficient sucrose extraction at the mill. At 12 months growth, 30–50% of reducing sugars was present in the stalk component, but at earlier stages was higher at 50–80%. Stalk yields of reducing sugars for 12 month crops were less than 100 g m−2, which was less than 5% of total sugars in the stalk. There were strong effects of N supply and cultivar on the amounts and concentration of reducing sugars in the stalk at low yields, but little effect when stalk biomass exceeded about 4000 g m−2 suggesting that, agronomic or genetic manipulation of levels of reducing sugars will only be effective early in the season. For a given level of stalk biomass, cultivar effects on partitioning to reducing sugars were due either to differences in partitioning of stalk biomass to total sugars, or differences in the partitioning between sucrose and reducing sugars. On the other hand, variation in N supply only altered the partitioning between sucrose and reducing sugars. Calculations suggested that high concentrations of reducing sugars in stalks harvested at a young age or from high N supply treatments, were not expected to lower the polarimetric estimate of sucrose concentration in the juice by more than 6%. This study provides a framework to assess the impact of cultivar, crop duration, and N supply on the accumulation of reducing sugars in different production systems.  相似文献   

11.
《Field Crops Research》2004,85(2-3):135-148
Seed N concentration is one of the main quality parameters in grain legume crops. Since few studies have aimed at modelling both seed and vegetative parts N concentrations, our objective was to model N partitioning between vegetative parts and filling seeds for pea (Pisum sativum L.) in field situations where both N nutrition and the plant genotype varied. A crop model component predicting the time courses of vegetative and seed N concentrations was built using knowledge concerning N partitioning during the seed filling period, which include a previously demonstrated relationship between the rate of individual seed N accumulation and the N availability within plants. A greenhouse experiment where assimilate availability was non-limiting was conducted with two genotypes. This experiment demonstrated the genotypic variability of one of the crop model component parameters, the maximum rate of individual seed N accumulation (SNRmax), allowing introduction of this parameter in the crop model component for the studied genotypes. Field experiments spanning 3 years and comprising various crop N nutrition and four genotypes were conducted to evaluate the crop model component. Observed seed and vegetative parts N concentrations ranged at harvest from 19.3 to 39.1 mg g−1 and from 3.6 to 18.4 mg g−1, respectively. N partitioning was well-simulated by the crop model component except when crops had deficient N nutrition. These results suggest that the parameter “NCn-remob” (proportion of N in vegetative parts which is not available for remobilization to filling seeds), which is taken as constant in the crop model component, could depend upon the crop nutrition level. A sensitivity analysis highlights the need for a precise calibration of the parameters “NCn-remob” and “SNRmax”. When the crop N nutrition level and further genotypic variability of these parameters are incorporated in the proposed crop model component, it will become a useful part of a pea crop model predicting yield and seed N concentration.  相似文献   

12.
Summary In the Netherlands seed potato crops are harvested when still green, the haulm being destroyed before harvest. We compared the effect on the contamination of seed potatoes byErwinia carotovora subsp.atroseptica (Eca) andE. chrysanthemi (Ech) of the common method of haulm destruction by flailing and chemically destroying remaining stems, with the recently developed green crop lifting method. After chenical haulm destruction the levels of contamination with both Eca and Ech surviving cold storage were found not to differ significantly from those after green crop lifting. Losses due to watery wound rot (Pythium ultimum) were considerable in the warm and humid conditions during 1991, especially after green crop lifting.  相似文献   

13.
Break crop benefits in temperate wheat production   总被引：4，自引：0，他引：4  
Changes in the sequence of crops grown on agricultural land are well known to enhance the yield of grain crops such as wheat. A survey of the literature gathered from around the world show mean yield benefits of up to 20% or more. Much is known about the principal mechanisms responsible for these benefits, including effects on disease control, improved nitrogen nutrition and water supply, although researchers continue to be challenged by inexplicable “rotation effects” that have yet to be documented or fully understood. This review summarizes our current understanding of the ‘better-known’ mechanisms of crop rotation, and discusses other mechanisms (e.g. changes in rhizosphere biology, allelopathy or soil structure) that may help to account fully for the rotation benefits that have been observed by agricultural producers for more than 2000 years. Where possible we emphasise new techniques employed to investigate these less well-understood aspects of the “rotation effect”. At the farm level, the inability to capitalize on the benefits of break crops may owe more to economics, the availability of suitable break crops and the complexity of the crop response. Computer-based decision support tools have been developed to assist growers to apply the information gathered from scientific studies, although efforts to integrate this information at whole-farm scales are embryonic.  相似文献   

14.
The impact of tillage system, rotation sequence and foliar fungicides on diseases and seed yield and quality of wheat, barley, pea, canola and flax was determined in the second cycle of three, 4-year rotations from 1998 to 2001 on a Black Chernozem (Udic Boroll) at Melfort, Saskatchewan, Canada. The objective of the study was to evaluate the impact of reduced-tillage production systems, broadleaf cropping intensity and fungicide use on cereal, oilseed and pulse crops in northeastern Saskatchewan, a sub-humid region of the northern Great Plains. A split-split plot design was used with three tillage systems (conventional, minimum and no-till) as main plots, three rotations of increasing broadleaf crop intensity (1. canola-wheat-barley-barley; 2. canola-barley-pea-wheat; and 3. canola-pea-flax-barley) as sub-plots, and fungicide treatments (treated or untreated) as sub-sub-plots. Fungicides appropriate for the diseases of concern were applied at recommended crop development stages and application rates, followed by assessment of diseases. Tillage system had little impact on diseases of any crop, although seed yield was usually greater under no-till for most crops under dry conditions. Rotation was not a major factor in disease severity of most of the crops, except barley in the rotation where it was grown for two consecutive years. Under dry conditions, barley yield was reduced when it followed flax compared with other crops, most likely due to less available soil moisture after flax. Fungicide application had the greatest impact on disease control and seed yield increase, although results varied among crops and years. In conclusion, the findings indicate that tillage system had little effect on disease severity, rotation contributed to greater disease severity only when a crop was grown intensively, such as on its own stubble, and fungicide application had variable effects on both disease control and seed yield.  相似文献   

15.
David B. Lobell   《Field Crops Research》2007,100(2-3):210-217
Uncertainties in soil nitrogen (N) supply and crop N demand present a challenge to farmers deciding on N fertilizer rates. While field studies have documented the improvements in N use efficiency possible with site-specific N management approaches that address these uncertainties, a general understanding of the importance of uncertainty across a wide range of cropping systems is yet to emerge. Here a general model of N rate decision-making is presented which computes the optimal N rate that maximizes expected profit given uncertainties in N supply and demand. The cost of uncertainty is measured as the difference in N rate when soil N supply and crop N demand are unknown versus known perfectly. Eliminating uncertainty in soil N supply (but not crop demand) would reduce average N rates by 5–15% in typical irrigated rice systems, 10–30% in wheat, and 20–40% in maize. Perfect knowledge of potential crop N demand (but not soil supply) would reduce rates by 3–10% in all systems. Simultaneous knowledge of both factors reduced N rates by significantly more than the sum of their individual effects, reflecting important interactions between supply and demand uncertainties. This indicates that the value of information for one factor is inversely related to the level of uncertainty in the other. Studies that separately consider information on soil N supply or crop N demand may therefore underestimate the total benefit of management approaches that address both these uncertainties. Site-specific N management could lead to substantial reductions of N rates without yield loss in a wide range of cropping systems, thereby improving profitability and environmental quality.  相似文献   

16.
Soilborne potato diseases are persistent problems in potato production. Use of disease-suppressive rotation crops, such as Brassica spp. (mustards, rapeseed) and sudangrass, has shown potential for management of soilborne diseases and enhanced yield in various crop production systems. However, how to best implement these crops into productive potato cropping systems has not yet been determined. In this research, potential disease-suppressive crops were evaluated under four different types of production management (as a cover crop, green manure, harvested crop-residue incorporated, and harvested crop-residue not incorporated) in potato rotation field trials, and their effects on disease, yield, and economic viability determined. Mustard blend, sudangrass, and rapeseed rotations reduced the tuber disease black scurf (by 16–27 %) and increased yield (by 6–11 %) relative to a barley rotation control, but only mustard blend consistently reduced common scab (by 11 %). All rotation crops managed as green manures produced lower disease (by 15–26 %) and higher yields (by 6–13 %) than other management practices. Overall, the combination of mustard blend managed as a green manure was most effective, reducing scurf by 54 % and increasing yield by 25 % relative to a soybean cover crop. The use of mustard or rapeseed as a harvested crop with incorporation provided the best economic return, increasing net income by more than $860/ha relative to the standard barley rotation, but mustard blend grown as a green manure or non-incorporated harvest crop also substantially increased net income ($600 to $780/ha).  相似文献   

17.
Agricultural drought occurs when there is a deficit in soil water supply to crops. Severe drought limits crop water availability and reduces yield. Rainfed crop production is very vulnerable to drought conditions and farmers in northeast of Iran who heavily depend on their rainfed cereals production usually suffer from drought occurrence. Based on history, any severe drought resulted in severe financial problems and forced the affected farmers to move to cities in search of alternative jobs. Any possibility to enable the farmers to mitigate or adapt to drought is highly required. In this study, the relationship between aridity index (AI) and detrended crop yield (1985–2005) of selected crops (wheat and barley) and the influence of three climate indices (AO, NAO and NINO-3.4) were assessed for Khorasan province in northeast of Iran. All associations were assessed at annual, seasonal (wet and dry seasons) and monthly scale considering both concurrent and lag correlations (1-year and 2-year lag). Our results indicated a significant correlation (P < 0.05) between the AI and crops yield mostly in central Khorasan province. Our study also showed that correlation coefficient between AI and barley yield was stronger than AI and wheat yield across all study locations. Seasonal (wet) AI showed significant correlation with crops yield. These results demonstrated that, in some areas of Khorasan, drought is one of the key causes of interannual yield variability. We also observed a significant association between NAO and NINO-3.4 with AI. Precipitation is one of the components of AI, so AI response to NAO and NINO-3.4 can be related to the observed association between this index and precipitation. It seems that these indices could be useful tools to monitor drought patterns and subsequent yield variability in some regions of Khorasan province.  相似文献   

18.
《Field Crops Research》1998,55(3):201-208
In irrigated sugarcane production, water is usually withheld prior to harvest to dry the field and to raise the sucrose content of the cane. Past research has provided conflicting results on the optimum length of drying-off. An analysis was conducted of pooled data from 37 experiments on drying-off in Southern Africa to: (1) determine the range of responses in sucrose yield and cane sucrose concentration that have been attained under various drying-off regimes; (2) quantify the trade-off between the loss in cane yield under drying-off and any possible gain in sucrose yield and cane sucrose fresh weight (FW) concentration; and (3) identify which components of sucrose yield and sucrose concentration are most sensitive to late-season water deficit, as a means of developing functions for crop simulation models. In only 22% and 61% of the drying-off treatments was there a significant increase in sucrose yield or sucrose FW concentration, respectively. For both sucrose yield and sucrose FW concentration, the average increase attained by drying-off was 8% and the maximum increase was about 15%. Increase in sucrose yield occurred when the decrease in stalk dry mass was no greater than about 10%. This relationship could form the basis for determining the trade-off between reduction in stalk mass and sucrose yield under varying drying-off regimes, and developing economic optima for drying-off severity. Increase in sucrose FW concentration occurred due to an increase in soluble solids and dehydration. Small reductions in fresh yield of cane under drying-off (up to 10%) can be attributed equally to dehydration and reduction in stalk dry mass.  相似文献   

19.
Under semiarid Mediterranean conditions irrigated maize has been associated to diffuse nitrate pollution of surface and groundwater. Cover crops grown during winter combined with reduced N fertilization to maize could reduce N leaching risks while maintaining maize productivity. A field experiment was conducted testing two different cover crop planting methods (direct seeding versus seeding after conventional tillage operations) and four different cover crops species (barley, oilseed rape, winter rape, and common vetch), and a control (bare soil). The experiment started in November 2006 after a maize crop fertilized with 300 kg N ha−1 and included two complete cover crop-maize rotations. Maize was fertilized with 300 kg N ha−1 at the control treatment, and this amount was reduced to 250 kg N ha−1 in maize after a cover crop. Direct seeding of the cover crops allowed earlier planting dates than seeding after conventional tillage, producing greater cover crop biomass and N uptake of all species in the first year. In the following year, direct seeding did not increase cover crop biomass due to a poorer plant establishment. Barley produced more biomass than the other species but its N concentration was much lower than in the other cover crops, resulting in higher C:N ratio (>26). Cover crops reduced the N leaching risks as soil N content in spring and at maize harvest was reduced compared to the control treatment. Maize yield was reduced by 4 Mg ha−1 after barley in 2007 and by 1 Mg ha−1 after barley and oilseed rape in 2008. The maize yield reduction was due to an N deficiency caused by insufficient N mineralization from the cover crops due to a high C:N ratio (barley) or low biomass N content (oilseed rape) and/or lack of synchronization with maize N uptake. Indirect chlorophyll measurements in maize leaves were useful to detect N deficiency in maize after cover crops. The use of vetch, winter rape and oilseed rape cover crops combined with a reduced N fertilization to maize was efficient for reducing N leaching risks while maintaining maize productivity. However, the reduction of maize yield after barley makes difficult its use as cover crop.  相似文献   

20.
The effects of applying nitrogen (30 or 40 kg N/ha) to wheat crops at and after anthesis, after 200 kg N/ha had already been applied to the soil during stem extension, were studied in field experiments comprising complete factorial combinations of different cultivars, fungicide applications and nitrogen treatments. Actual recoveries of late-season fertilizer nitrogen (LSFN), as indicated by 15N studies, interacted with cultivar and fungicide treatment, and depended on nitrogen source (urea applied as a solution to the foliage, or as ammonium nitrate applied to the soil) and year. These interactions, however, were not reflected in apparent fertilizer recoveries ((N in grain with LSFN − N in grain without LSFN)/N applied as LSFN), or in the crude protein concentration. Apparent fertilizer recovery was always lower than actual recoveries, and declined during grain filling. Fertilizer treatments with higher actual fertilizer recoveries were associated with lower net remobilisation of non-LSFN (net remobilised N = N in above ground crop at anthesis − N in non-grain, above ground crop at harvest). LSFN also increased mineral nitrogen in the soil at harvest even when applied as a solution to the foliage. These effects are discussed in relation to potential grain N demand.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号