Relative Crop Yield Research Articles

Energy inputs and crop yield relationship in potato production in Hamadan province of Iran

The aim of this study was to determine energy consumption and the relationship between energy input and yield for potato production in Kaboud Rahang region of Hamadan state. The data used in this study are collected by questionnaire. The results revealed that nitrogen fertilizer (39%), diesel (21%), seed (14.9%), water (7.5%) and manure (6.4%) consumed the bulk of energy. In the surveyed farms, average yield and energy consumption were calculated as around 28613.7 kg/ha, 92296.3 MJ/ha, respectively. The results also showed that energy ratio, specific energy and energy productivity were 1.1, 3.2 MJ/kg and 0.3 kg/MJ, respectively. An econometric model was developed to estimate the impact of energy inputs on yield by using parametric methods. For this purpose, potato yield, an endogenous variable was assumed to be a function of energy inputs: fertilizer manure, chemical, machinery, human, water for irrigation, diesel and seed. The empirical results indicated that variables: fertilizer, chemical, seed and human were found statistically significant and contributed to yield. Among statistically significant exogenous variables, seed, water for irrigation, chemical, human and fertilizer were ranked in terms of elasticities.

Competitive and allelopathic interference between soybean crop and annual wormwood ( Artemisia annua L.) under field conditions

Annual wormwood interference on soybean crop growth and yield may result from competition and allelopathy, which are modulated by crop management. Allelochemicals released by annual wormwood (e.g. artemisinin) may affect the crop directly or indirectly through the effect on the nitrogen fixing symbiont, Bradyrhizobium japonicum. The objectives were (i) to quantify the crop response (i.e. biomass production, nodulation and yield) to weed interference and (ii) to determinate the relative change of competition and allelopathy interferences, when a sublethal dose of herbicide is applied. Two split plot field experiments with three replications were used. The experiment involved a factorial combination of five weed–crop density (soybean/annual wormwood, plants m −2) levels: D1, pure soybean, 40/0 plants m −2; D2, 40/2 plants m −2; D3, 40/4 plants m −2 and D4, 40/8 plants m −2, and D5, pure annual wormwood, 0/8 plants m −2, two activated carbon (allelopathy) levels: C−, with activated carbon (reduced allelopathy) and C+, non activated carbon applied (with allelopathy) and two herbicide levels: H−, untreated and H+, treated with a sub-lethal dose of glyphosate. Activated carbon to adsorb allelochemicals (with and without activated carbon) and glyphosate application (with and no herbicide) were assigned to sub-plots. Increasing weed density did not affect crop biomass at flowering, but changed nodule number and soybean yield with a different pattern depending on carbon and herbicide treatment. Relative crop yield decreased with increasing relative weed biomass. This decrease was particularly drastic when allelopathy was reduced by activated carbon and without herbicide application. The maximum yield losses of 33% in 2006 and 17% in 2007 were observed with the highest weed density (8 plants m −2). In contrast, without carbon (high allelopathy level), soybean yield remained stable within the explored range of annual wormwood biomass, despite the fact that weed biomass at high densities (D4) was high enough to generate competition. The lack of response to increasing weed density could be related to the indirect effect of allelochemicals interacting with soil microorganisms (i.e. B. japonicum) that positively affected the nodulation (e.g. larger nodules in 2006 and increased nodules biomass due to higher number of roots in 2007 at high densities). With herbicide application, soybean yield of both carbon treatments remained stable when biomass of annual wormwood increased. This research provided strong evidence in support of the existence of positive effect of allelopathic and competitive interactions between annual wormwood and soybean crop under field conditions that may be overridden under herbicide application.

Planning for Deficit Irrigation

Irrigators with limited water supplies that lead to deficit irrigation management need to make decisions about crop selection, water allocations to each crop, and irrigation schedules. Many of these decisions need to occur before the crop is planted and depend on yield-evapotranspiration (ET) and yield-irrigation relationships. The Kansas Water Budget (KSWB) predicts crop yields from inputs of daily weather parameters to calculate reference ET (ETr) and irrigation and precipitation events to calculate a soil water balance. Results from the KSWB were compared with data from a 4-year field study conducted in southwest Kansas. The field study had one irrigation treatment to meet full irrigation requirements and five deficit irrigation treatments. Average soil water contents from field data on discrete days during the growing season compared well with KSWB results, but field soil water contents varied among each irrigation treatment replication. Relative crop yields and crop ET (ETc) compared well with KSWB results for the fully irrigated treatment, but the KSWB results tended to underestimate field results as irrigation declined. These differences may be attributed to calibrations of the KSWB with historical data from conventional (tilled) management in contrast to the field study which was managed with no-till techniques. Field and KSWB yield-ET relationship results were almost identical. The KSWB can be a tool for deficit irrigation management decisions that need predictions of crop yields for planning crop rotations, allocations of irrigation to selected crops, and screening of anticipated irrigation schedules.

Weed–crop competition relationships differ between organic and conventional cropping systems

SummaryExperiments comparing conventional and organic systems often report similar yields despite substantially higher weed abundance in the organic systems. A potential explanation for this observation is that weed–crop competition relationships differ between the two types of systems. We analysed weed and crop yield data from the Rodale Institute Farming Systems Trial (FST), which provides a unique 27‐year dataset of a conventional (CNV) and two organic [manure (MNR) and legume (LEG)] soyabean (Glycine max (L.) Merr.) and maize (Zea mays L.) cropping systems. Average soyabean yields were similar between the MNR and CNV systems and only slightly reduced in the LEG system, whereas average maize yields did not differ among systems despite the two organic systems having more than four and six times greater weed biomass in soyabean and maize respectively. Plot‐level weed biomass–crop yield relationships indicated that weed–crop competition differed between the two organic and CNV systems in maize, and was strongest in the CNV system, intermediate in the LEG system and weakest in the MNR system. These results suggest that organic cropping systems may be able to tolerate a greater abundance of weeds compared to conventional systems and that fertility management within organic systems may influence weed–crop competition.

Effect of Planting Date on <I>Lissorhoptrus oryzophilus</I> (Coleoptera: Curculionidae) Density–Yield Relationship on Rice in Southeastern Texas

Results of planting date and insecticide efficacy experiments targeting Lissorhoptrus oryzophilus Kuschel (Coleoptera: Curculionidae) on rice, Oryza sativa L., in southeastern Texas between 2002 and 2007 were used to determine density-yield relationships as a function of planting date. Soil core samples were collected on two dates during main crop development to estimate immature L. oryzophilus populations followed by main and ratoon crop harvests. Analysis of covariance (ANCOVA) revealed that planting date did not affect the density-main crop yield relationship during most years and that these relationships varied substantially among years. For ratoon crop yield, an effect of main crop L. oryzophilus immature infestation was detected during some years, but the real effect of these populations on ratoon crop yield remains unclear. Using estimates of yield reduction per L. oryzophilus immature, economic injury levels were calculated. Main crop yields from treated plots and first soil core sample L. oryzophilus immature populations from untreated plots were significantly higher in plots planted at recommended dates than in plots planted earlier or later. This suggests that the presence of high populations of reproductive L. oryzophilus coincides with the period when rice fields planted at optimum dates are flooded. Results from this study reinforce the importance of managing L. oryzophilus populations when planting rice at recommended dates in southeastern Texas.

Irrigation Water Quality and Crop Yield Relationship Established for Kaithal Irrigation Circle of Bhakra System

Salinity is one of the major problems of irrigated agriculture all over the world. More than 60 % of the land is underlain by saline ground water in North West India. The knowledge of relationship between irrigation water quality (EC) and crop yield is essential for management of surface water and ground water for higher profitability. In the present study, an attempt was made to evaluate the irrigation water quality and wheat yield relationship for Kaithal irrigation circle of Bhakra canal command. Information on EC, agronomic practices, crop yield etc. were collected from 108 farms comprising 36 farms each from head, middle and tail watercourses of Batta minor. The presence of different quality of ground water creates large variation in crop yield. To establish a relationship between irrigation water quality and crop yield of wheat, several types of functions were tried and form of relationship generating highest correlation coefficient was selected as most appropriate relationship. The polynomial equation of fifth order was most suitable for irrigation water quality and crop yield relationship. This relationship can be used for estimating wheat yield with different quality of water. The groundwater of the tail reaches being saline in nature was about 25% less productive as compared to head reaches. The wheat yield in the tail was less by 10% as compared to head reaches due to unavailability of canal water and poor quality of ground water. Groundwater transfer from head to tail reaches and cultivation of low water requiring salt tolerant crop would be helpful in reducing the productivity gap and increasing the profitability of the farmers.

Seasonal climate change impacts on evapotranspiration, precipitation deficit and crop yield in Puerto Rico

The purpose of this study was to estimate precipitation ( P), reference evapotranspiration (ET o), precipitation deficit (PD = P − ET o) and relative crop yield reduction (YR) for a generic crop under climate change conditions for three locations in Puerto Rico: Adjuntas, Mayagüez, and Lajas. Reference evapotranspiration was estimated by the Penman–Monteith method. Precipitation and temperature data were statistically downscaled and evaluated using the DOE/NCAR PCM global circulation model projections for the B1 (low), A2 (mid-high) and A1fi (high) emission scenarios of the Intergovernmental Panel on Climate Change Special Report on Emission Scenarios. Relative crop yield reduction was estimated from a water stress factor, which is a function of soil moisture content. Average soil moisture content for the three locations was determined by means of a simple water balance approach. Results from the analysis indicate that the rainy season will become wetter and the dry season will become drier. The 20-year average September precipitation excess (i.e., PD > 0) increased for all scenarios and locations from 121 to 321 mm between 2000 and 2090. Conversely, the 20-year average February precipitation deficit (i.e., PD < 0) changed from −27 to −77 mm between 2000 and 2090. The results suggest that additional water could be saved during the wet months to offset increased irrigation requirements during the dry months. The 20-year average relative crop yield reduction for all scenarios decreased on average from 12% to 6% between 2000 and 2090 during September, but increased on average from 51% to 64% during February. Information related to the components of the hydrologic water budget (i.e., actual evapotranspiration, surface runoff, aquifer recharge and soil moisture storage) is also presented. This study provides important information that may be useful for future water resource planning in Puerto Rico.

PLANNING LENGTH OF LONG -TERM FIELD EXPERIMENTS THROUGH DECISION SUPPORT SYSTEMS – A CASE STUDY

Long-term field experiments are the conventional means for developing; evaluating and demonstrating site-specific land/water use plans. However, it has been often observed that at times they are unable to propose sustainable practices, when planned for shorter time durations (say 2-3 years) or become cost-ineffective and obsolete, when planned for longer time durations (say more than 15 years or so). Hence, what should be the ideal length of such long-term experiments has always been a debatable issue. The present study attempts to demonstrate application of one indigenously developed decision support system (DSS) for planning appropriate length of long term conjunctive water use experiments on a test salt affected farmer’s field. Before application the proposed DSS was extensively validated on several farmers and controlled experimental fields in Haryana (India). Validation of DSS showed its potential to give realistic estimates of root zone soil salinity; sodicity and salt stress induced relative crop yield reductions under local resource management conditions. Long term impact assessment of varied conjunctive water use strategies, on the test farmer’s field, with the so validated DSS showed that the time required for achieving stable crop yields could be treated as a good measure of the minimum length of such experiments. For the test (rice-wheat growing) farmer’s field, this time ranged between 5.5 – 6.0 years. It was observed that at shorter time scale (i.e. 2 years), though application of 50% canal waters (CW) blended with 50% tube well waters (TW), was as productive and superior as cyclic applications of (2CW, 1TW, 1CW); (1CW, 1TW, 2CW) and (CW: TW) during wheat cropping season yet it could not maintain its superior performance at DSS proposed time duration of 6 years or more. Similarly irrigation practice of (4CW, 5TW) during rice cropping season, though beneficial at shorter time scale, was much inferior to the cyclic application of canal and tube well waters (i.e. CW: TW) at longer time scales (i.e. at ≥ 6 years). Hence, limiting the proposed long-term conjunctive water use experiment to the DSS proposed minimum time duration of 6 years lead to the selection of the most stable and sustainable irrigation practice(s) for the test farm.

Simulated effect of drainage water management operational strategy on hydrology and crop yield for Drummer soil in the Midwestern United States

The hypothetical effects of drainage water management operational strategy on hydrology and crop yield at the Purdue University Water Quality Field Station (WQFS) were simulated using DRAINMOD, a field-scale hydrologic model. The WQFS has forty-eight cropping system treatment plots with 10 m drain spacing. Drain flow observations from a subset of the treatment plots with continuous corn ( Zea mays L.) were used to calibrate the model, which was then used to develop an operational strategy for drainage water management. The chosen dates of raising and lowering the outlet during the crop period were 10 and 85 days after planting, respectively, with a control height of 50 cm above the drain (40 cm from the surface). The potential effects of this operational strategy on hydrology and corn yield were simulated over a period of 15 years from 1991 to 2005. On average, the predicted annual drain flows were reduced by 60% (statistically significant at 95% level). This is the most significant benefit of drainage water management since it may reduce the nitrate load to the receiving streams. About 68% of the reduced drain flow contributed to an increase in seepage. Drainage water management increased the average surface runoff by about 85% and slightly decreased the relative yield of corn crop by 0.5% (both are not statistically significant at 95% level). On average, the relative yield due to wet stress (RYw) decreased by 1.3% while relative yield due to dry stress (RYd) increased by 1%. Overall, the relative crop yield increased in 5 years (within a range of 0.8–6.9%), decreased in 8 years (within a range of 0.2–5.5%), and was not affected in the remaining 2 years. With simulated drainage water management, the water table rose above the conventional drainage level during both the winter and the crop periods in all years (except 2002 crop season). The annual maximum winter period rise ranged between 47 cm (1995) and 87 cm (1992), and the annual maximum crop period rise ranged between no effect (2002) and 47 cm (1993).

Climate–crop yield relationships at provincial scales in China and the impacts of recent climate trends

Understanding climate-yield relationships and the impacts of recent climate trends on crop productivity on a large scale is an important step in predicting regional agricultural production. In this study we investigated climate-crop relationships, recent trends in seasonal climate (maximum and minimum temperatures, diurnal temperature range and precipitation) and their impacts on the yields of major crops (i.e. rice, wheat, maize and soybean) at provincial scales throughout China over the last few decades. We found that major crop yields were significantly related to growing season climate in the main production regions of China, and that growing season temperature had a gener- ally significant warming trend. Due to the trends in growing season climate, total rice production in China was estimated to have increased by 3.2 × 10 5 t decade -1 during the period 1951-2002; total pro- duction of wheat, maize and soybean changed by -1.2 × 10 5 , -21.2 × 10 5 and 0.7 × 10 5 t decade -1 , respectively, during 1979-2002. The warming trend increased rice yield in northeast China and soy- bean in north and northeast China; however, it decreased maize yield in 7 provinces (autonomous region or municipality) and wheat yield in 3 provinces. Our analysis presents the general response patterns of regional agricultural productivity to seasonal climate variability and change over the last few decades. Crop response mechanisms to local seasonal climate change (and variability) need further investigation to better understand the patterns and predict future consequences of climate change and variability on regional agricultural production.

Relating crop yield to topographic attributes using Spatial Analysis Neural Networks and regression

Land-surface topographic attributes can be useful for estimating stable spatial patterns of crop yield caused by spatial variability in soils and water availability. We present spatial analyses of grain yield for three fields of dryland winter wheat in northeastern Colorado using topographic attributes as explanatory variables. Topographic attributes including elevation, slope, aspect, curvature, specific contributing area, and wetness index were computed from a 10-m digital elevation model. A Spatial Analysis Neural Network (SANN) algorithm was used for joint spatial interpolation and yield prediction from the topographic attributes. SANN prediction errors were compared with the results of Multiple Linear Regression (MLR). SANN and MLR were assessed in terms of bias and relative root mean squared error (rRMSE) using validation data. SANN out-performed MLR in multivariate estimation, but not for the univariate cases. The greatest advantage of SANN was seen using four or more topographic attributes, whereas MLR showed diminishing efficiency with more than three explanatory variables. Prediction/interpolation errors within a given field were reduced substantially by using the spatial coordinates (latitude and longitude) in tandem with topographic attributes. The rRMSE value reached a minimum of 0.44 (model efficiency, E = 0.80) for interpolation with SANN on the West field. Using only topographic attributes as input, the minimum rRMSE values were 0.59 ( E = 0.65) for SANN with 5 variables and 0.72 ( E = 0.48) for MLR with 4 or 5 explanatory variables. Thus, this study demonstrated the utility of SANN with topographic attributes that contain implicit soil and water information for estimating spatial patterns of dryland crop yield.

Long‐term effects of various crop rotations for managing salt‐affected soils through a field scale decision support system – a case study

AbstractAppropriate crop rotations coupled to water use plans are the basic means of managing salt‐affected soils. Recommendation of suitable crop rotations for salt‐affected land requires prediction of their long‐term impact on soil salinity/sodicity build‐up and consequent crop yield reduction. This is conventionally achieved through long‐term field experiments. However, such evaluations are site specific, expensive and time consuming. Appropriate decision support systems (DSS) can be a cost‐effective means in such cases. This study demonstrates the application of one such DSS for recommending the best crop rotation for a salt‐affected field in Gurgaon district of Haryana (India). Before application, the DSS was extensively validated on 11 farmer's fields and one experimental field in Gurgaon and Karnal districts of Haryana. The DSS gave realistic estimates of root zone soil salinity/sodicity and relative crop yield reductions under the local management practices. These estimates were associated with absolute mean relative errors ranging between 0.02 and 0.24. Ten‐year impact assessments of existing (i.e. paddy–wheat, P‐W) and 10 alternative crop rotation plans with the validated DSS showed that pearl millet‐based sequences were, environmentally and agronomically, the most suitable options for the test field. However, a cost–benefit analysis of DSS‐simulated average annual crop yields, under various crop rotations, showed that the economic return of pearl millet‐based sequences was about 13% less than fallow–wheat (F‐W) rotations and 4% less than P‐W rotations. Hence F‐W was recommended as the most beneficial environmental choice and economically the most robust alternative crop sequence for the salt‐affected field.

Modelo computacional para suporte à decisão em áreas irrigadas. Parte II: testes e aplicação

Apresentou-se, na Parte I desta pesquisa, o desenvolvimento de um modelo computacional denominado MCID, para suporte à tomada de decisão quanto ao planejamento e manejo de projetos de irrigação e/ou drenagem. Objetivou-se, na Parte II, testar e aplicar o MCID. No teste comparativo com o programa DRAINMOD, espaçamentos entre drenos, obtidos com o MCID, foram ligeiramente maiores ou idênticos. Os espaçamentos advindos com o MCID e o DRAINMOD foram consideravelmente maiores que os obtidos por meio de metodologias tradicionais de dimensionamento de sistemas de drenagem. A produtividade relativa total, YRT, obtida com o MCID foi, em geral, inferior à conseguida com o DRAINMOD, devido a diferenças de metodologia ao se estimar a produtividade da cultura em resposta ao déficit hídrico. Na comparação com o programa CROPWAT, obtiveram-se resultados muito próximos para (YRT) e evapotranspiração real. O modelo desenvolvido foi aplicado para as condições do Projeto Jaíba, MG, para culturas perenes e anuais cultivadas em diferentes épocas. Os resultados dos testes e aplicações indicaram a potencialidade do MCID como ferramenta de apoio à decisão em projetos de irrigação e/ou drenagem.

06/02772 Energy inputs and crop yield relationship in greenhouse tomato productionHatirli, S. A. et al. Renewable Energy, 2006, 31, (4), 427–438

06/02772 Energy inputs and crop yield relationship in greenhouse tomato productionHatirli, S. A. et al. Renewable Energy, 2006, 31, (4), 427–438

Impact Assessment and Recommendation of Alternative Conjunctive Water Use Strategies for Salt Affected Agricultural Lands through a Field Scale Decision Support System – A Case Study

Conjunctive use of saline/non-saline irrigation waters is generally aimed at minimizing yield losses and enhancing flexibility of cropping, without much alteration in farming operations. Recommendation of location-specific suitable conjunctive water use plans requires assessment of their long-term impacts on soil salinization/sodification and crop yield reductions. This is conventionally achieved through long-term field experiments. However such impact evaluations are site specific, expensive and time consuming. Appropriate decision support systems (DSS) can be time-efficient and cost-effective means for such long-term impact evaluations. This study demonstrates the application of one such (indigenously developed) DSS for recommending best conjunctive water use plans for a, rice-wheat growing, salt affected farmer's field in Gurgaon district of Haryana (India). Before application, the DSS was extensively validated on several farmers and controlled experimental fields in Gurgaon and Karnal districts of Haryana (India). Validation of DSS showed its potential to give realistic estimates of root zone soil salinity (with R = 0.76-0.94; AMRE = 0.03-0.06; RMSPD = 0.51-0.90); sodicity (with R = 0.99; AMRE = 0.02; RMSPD = 0.84) and relative crop yield reductions (AMRE = 0.24), under existing (local) resource management practices. Long term (10 years) root zone salt build ups and associated rice/wheat crop yield reductions, in a salt affected farmer's field, under varied conjunctive water use scenarios were evaluated with the validated DSS. It was observed that long-term applications of canal (CW) and tube well (TW) waters in a cycle and in 1:1 mixed mode, during Kharif season, predicted higher average root zone salt reductions (2-9%) and lower rice crop yield reductions (4-5%) than the existing practice of 3-CW, 3-TW, 3-CW. Besides this, long-term application of 75% CW mixed with 25% TW, during Rabi season, predicted about 17% lower average root-zone salt reductions than the cyclic applications of (1-CW, 1-TW, 2-CW) and (2-CW, 1-TW, 1-CW, i.e., existing irrigation strategy). However, average wheat crop yield reductions (16-17%) simulated under all these strategies were almost at par. In general, cyclic-conjunctive water use strategies emerged as better options than the blending modes. These results were in complete confirmation with actual long-term conjunctive water use experiments on similar soils. It was thus observed that such pre-validated tools could be efficient means for designing, local resource and target crop yield-specific, appropriate conjunctive water use plans for irrigated agricultural lands.

Energy inputs and crop yield relationship in greenhouse tomato production

This study examines energy use patterns and the relationship between energy inputs and yield for greenhouse tomato production in Antalya province of Turkey. The data used in this study were based on cross-sectional data collected from growers by using a face to face survey. The results revealed that diesel (34.35%), fertilizer (27.59%), electricity (16.01%), chemicals (10.19%) and human power (8.64%) consumed the bulk of energy. In the surveyed farms, average yield and energy consumption were calculated as around 160000 kg/ha and 106716.2 MJ/ha, respectively. The results also showed that output–input, specific energy and energy productivity were 1.2, 12380.3 MJ/t and 0.09 kg/MJ, respectively. The results implied that small size farms were more efficient than large ones in terms of output–input ratio. An econometric model was developed to estimate the impact of energy inputs on yield. Therefore, tomato yield, an endogenous variable was assumed to be a function of exogenous variables; fertilizer, chemicals, machinery, human, water for irrigation and seed energy. The empirical results indicated that all exogenous variables except seed energy were found statistically significant and contributed to yield. Among all statistically significant exogenous variables, human, fertilizer, water, chemicals and machinery were ranked in terms of elasticities. These results indicate that the Turkish greenhouse industry heavily depends on fossil fuels.

Effect of field groundwater table control on water and salinity balance and crop yield in the Qingtongxia Irrigation District, China

AbstractThe Qingtongxia Irrigation District (QID) is one of the key agricultural bases in the Yellow River Basin. It is located in the upstream part of the Yellow River in the north of China and covers about 350 000 ha of farmland. The climate in the district is arid and semi‐arid. The annual average precipitation is about 200 mm. Water shortage is one of the main restrictions on agricultural development. In recent years, large amounts of water have been drawn from the Yellow River, which not only contributes to the severity of water shortages in the middle and downstream part of the Yellow River Basin, but also leads to the rise of the groundwater table and related waterlogging and salinization of the farmland.This article focuses on the analysis of the effects of field groundwater table control under different irrigation water amounts on the soil water and salinity content and on relative crop yield. Two experimental areas, Pingluo and Huinong, were selected to collect the required field data. The agro‐hydrological model SWAP was used to analyse the water flow and salt transport for different groundwater table and irrigation scenarios. Six scenarios, which resulted from two groundwater table regimes combined with three irrigation amounts, were simulated. The groundwater table regimes represent the present and future target groundwater table situation and the three irrigation amounts represent different water‐saving options. Waterlogged land is also simulated. The results show that: High regional groundwater tables are the main reason for the large amount of drainage water and low crop yield. Due to the regional high groundwater table, reducing irrigation amounts in the field without lowering the field groundwater table will not lead to a large reduction of drainage water, and will cause a further reduction in crop yield. The salinity storage in the soil profile at the end of the growing season will increase when the irrigation amount is reduced, and when the groundwater table is lower. But the increase is very small. To lower the field groundwater to the target water table is an effective way to increase crop yield. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Definition of agroclimatic regions in Ireland using hydro-thermal and crop yield data

When compared to the agronomic aspects of agriculture the contribution of climate is poorly integrated into the body of scientific knowledge in Ireland. It is known that specific crops grow well in specific regions and that success of a crop can be related to climate factors. The aim of this paper was to derive agroclimatic regions of Ireland using hydro-thermal climate (as expressed by climographs using mean monthly rainfall and temperature) in conjunction with a statistical clustering technique ( k-means clustering) to relate crop yield, estimated using mathematical simulation models for grass, barley, maize, potato and soybean to hydro-thermal climate data. A dataset, on a 10 km×10 km grid, consisting of monthly radiation, rainfall, maximum temperature and minimum temperature was used to drive crop simulation models to predict average yields, for each grid square. Results showed that the crops simulated were sensitive to either available water or length of growing season. As there are few objective measures of the ideal number of clusters to use in order to create agroclimatic regions, clusterings to 3, 4 and 7 regions were evaluated against known properties of the Irish climate and crop responses. A seven cluster agroclimate region map was thought to be a good basis for describing Ireland’s agroclimates and was compared with climate data for the national synoptic station network. Results suggested a reasonably good correspondence between clusters and their associated synoptic observation stations. Some anomalies were observed. The resulting agroclimatic map could be used for extrapolation of empirical research findings, for agri-environmental experimental design and as a framework for assessment of the impact of climate change on Irish agriculture.

Technical and economic evaluation of some Striga control packages in maize in the Nigerian Guinea Savanna

Earlier reports have confirmed the technical feasibility and socio-economic acceptability of some integrated Striga control packages (ISCOPA) at farmers’ level. However, the performance of ISCOPA based on the synthetic varieties of maize have not been consistent. With the development of new open pollinated low management requiring Striga-tolerant maize varieties, further evaluation of the new packages has become necessary. In 1995, farmer-managed trials were, therefore, conducted at two locations Dakachi and Kaya in the Northern Guinea Savanna (NGZ) of Nigeria to compare the new ISCOPAS with the promising one reported earlier and relate crop yield to Striga/weed complex parameters. The ISCOPA tested had tolerant maize varieties, fertilizer application, weed control (pre-emergence herbicide application or hoe-weeding) and additional Striga control (post-emergence herbicide or hoe-weeding) as components. The ISCOPAs that had post-emergence herbicide components resulted in significantly higher maize grain yields than the farmers’ practice. Striga infestation was also significantly lower with the ISCOPAs containing post-emergence acifluorfen compared with the farmers’ practice. When three hoe-weedings replaced herbicide applications, only ISCOPAs of maize varieties 9022-13, Oba Super II and Acr 92 TZE produced higher yield than the farmers practice. Among the varieties, Oba Super 1 and 2 supported lower Striga shoot emergence than the farmers’ practice. However, all the improved varieties exhibited lower Striga syndrome reaction compared with farmers variety. The full ISCOPAs effectively reduced Striga shoot count and weed cover score and resulted in higher maize grain yield than the farmers’ practice. Maximum gross and net revenue were recorded from ISCOPAs containing codal (Metolachlor+Prometryne 1.0+1.0 kg a.i./ha) followed by post-emergence acifluorfen. The treatment also gave the highest return per naira invested in the control of Striga/weed complex.

Row Spacing Influences the Critical Timing for Weed Removal in Soybean (Glycine max)1

Row spacing affects the time of canopy closure, thus influencing the growth and development of both crop and weeds. Field studies were conducted in 1999, 2000, and 2001 at Mead, NE, and 2000 and 2001 at Concord in eastern Nebraska to determine the effects of three row spacings (19, 38, and 76 cm) on the critical time for weed removal (CTWR) in dryland soybean. A three-parameter logistic equation was fit to data relating relative crop yield to increasing duration of weed presence. In general, earliest CTWR occurred in the 76-cm rows, and coincided with the first trifoliate stage of soybean. Latest CTWR occurred in the 19-cm rows and coincided with the third trifoliate. The CTWR in 38-cm rows occurred at the second trifoliate. Practical implications are that planting soybean in wide rows reduces early-season crop tolerance to weeds requiring earlier weed management programs than in narrower rows.Nomenclature: Glyphosate-resistant soybean, Glycine max (L.) Merr.Additional index words: Integrated weed management, row spacing, timing of removal, weed interference.Abbreviations: CPWC, critical period of weed control; CTWR, critical time for weed removal; DAE, days after emergence; DM, dry matter; GDD, growing degree days; HTCs, herbicide tolerant crops; IWM, integrated weed management; POST, postemergence.