Late Maturing Maize Research Articles

Water use characteristics of an early and late maturing maize hybrid using stable isotopes

AbstractWater requirements of early‐maturing (EM) maize hybrids might be lower than those of late‐maturing (LM) maize hybrids. This study aimed to analyze the effects of different irrigation management on grain yield (GY), water uptake patterns, evaporation (E), and transpiration (T) of two maize hybrids differing in maturity via stable isotope method. The field experiment with 36 lysimeters (4‐m wide × 4‐m long) under rain‐shelters was conducted with an EM (DH518) and a mid‐maturing and LM (DH605) hybrid with three replicates from 2021 to 2022. Maize plants were grown under three irrigation amounts (W1, W2, and W3 were irrigated to maintain soil moisture at 45%, 60%, and 75% of field capacity, respectively) by flood irrigation (FI) and drip irrigation (DI) under rain‐out shelters. Results showed that GY and evapotranspiration (ET) of EM were 8% and 12% lower, while the crop water productivity (CWP) was 6% higher than that of LM. Water uptake of both hybrids occurred mainly within 0‐ to 60‐cm soil layer during the vegetative stage. Water uptake of both hybrids occurred mainly within 0‐ to 60‐cm soil layer during the vegetative stage. Summer maize under FI absorbed more water from the deep soil layer than DI in the late growth stage. Compared with LM, the water absorption depth of EM became shallower in the late growth stage. Water uptake of maize was mainly from the deeper soil under water stress conditions. E of total ET accounts for 43% under DI and 57% under FI; GY and CWP were 22% and 51% higher than those of FI. Together with choosing EM hybrids, optimization of water management with DIW3 could achieve higher GY and CWP. The optimization of irrigation method and hybrids could provide a reference for local farmers to improve GY and CWP.

Nitrogen Fertilizer Split Application Response on Late Maturing Maize ((Zea mays L.) at Banshure and Omonada Woredas, Sowthwest Ethiopia

The field experiments were carried out at Buno Bedele and Omonada Jimma Zones on farmers’ fields for three consecutive main seasons and two sites each. The 10 treatments were laid down in a randomized complete block design (RCBD) with three replications using (BH661) hybrid maize variety. All across season and location data analysis of ANNOVA showed that all parameters were significantly affected by different time of nitrogen applications including plant height, grain yield, and harvest index, above ground biomass and logging percentage. The two highest grain yield 6.48 and 6.47 was recorded from applying 1/3 at planting + 2/3 at flag leaf appearance stage and applying 1/2 at planting + 1/2 at 4-5 weeks after emerge (Positive control) respectively again this treatment gave 13.08 and 12.62 t ha-1 above ground biomass yield respectively. The highest grain yield has 78.24 and 23.00 % yield advantage over negative control and applying all recommended N rate at planting respectively. Again in economic analysis, the above treatments gave the highest 111660 and 111840 net benefit respectively. Even though the applying 1/3 at planting + 2/3 at flag leaf appearance treatment MMR was not acceptable. Therefore, based on the highest net benefit applying 1/2 at planting + 1/2 at 4-5 weeks after emerge (Positive control) and applying 1/3 at planting + 2/3 at flag leaf appearance nitrogen fertilizer split application on late maturing (BH661) maize variety give an economic yield response and also acceptable for farmers of study areas and similar agro ecology.

Management options for mid-century maize (Zea mays L.) in Ethiopia

This simulation study was carried out to assess the impact of climate change and adaptation strategies on maize production across 22 locations in Ethiopia using Decision Support System for Agrotechnology Transfer – Cropping System Model (DSSAT-CSM) CERES-Maize. Three maize varieties, i.e., [BH-660 (late maturing), BH-540 (medium maturing) and Melkasa-1 (short maturing)] along with three planting dates [early (25-Apr), normal (25-May) and late (25-Jun)], four N fertilizer rates (64, 96, 128 and 160 kg N/ha) and three water levels [rainfed (no irrigation), two irrigations (each 30 mm at time of flowering and 5 d after flowering with total = 60 mm) and five irrigations (each 30 mm at time of flowering to early grain-filing, which were applied every five days in total = 150 mm)] were evaluated as the adaptation strategy. The mid-century (2040–2069) temperatures and solar radiation were extracted from multiple model means across the Coordinated Regional Climate Downscaling Experiment (CORDEX) models under the highest Representative Concentration Pathway (RCP8.5). Maize productivity was evaluated assuming that maize was grown on shallow sandy loam soils. Yield of an early, medium and late maturing maize were changed by −13 to −8%, −10 to +4% and + 3 to +13%, respectively, relative to the baseline period (1980–2005). The days to maturity decreased by about 16%. Under rainfed condition, N application up to 64, 128 and 160 kg/ha significantly improved yield for early, medium and late maturing varieties, respectively. Relatively high yield and low inter-seasonal yield variability were simulated for BH-660 and Melkasa-1 when planted on 25-Apr and 25-May, respectively, for most locations. Application of two (60 mm) and five (150 mm) irrigation levels improved yield in drier locations. In conclusion, this study provides potential adaptation options under the future climate in maize producing regions of Ethiopia.

Water Use Efficiency Differences in Maize Varieties under Every Furrow and Alternate Furrow Irrigation

Water-use efficiency (WUE) differences of selected maize varieties under alternate and every furrow irrigation were investigated in a split-plot design trials with three replicates. Alternate furrow (AFI) and Every furrow irrigation (EFI) were main treatments and twenty maize varieties were sub-treatments. Plots were 64 m2 with one maize seed per station spaced at 0.25m apart. Crop water use results indicated that EFI consumed more water than the AFI. The AFI reduced crop water consumption by 38 - 45% compared to EFI.  Differences were also prominent in maize varieties’ response to AFI. Late maturing maize varieties proved to have minor yield reduction with AFI compared to early and medium maturing maize varieties. WUE (kg m-3) differed with irrigation water application strategy (P<0.001). AFI had high WUE. A combination of AFI with selection of water efficient maize varieties was a good strategy for improving WUE. The AFI is a promising furrow irrigation water management strategy for water saving. According to farmers experience at five irrigation schemes and on station research, it was concluded that AFI is one of the climate smart irrigation technique that farmer can easily adopt and apply as it saves labour, time water whilst reducing conflict for water among irrigators. It was recommended that AFI be applied fully on early and medium maturing maize varieties within an irrigation interval of 7 days. For late maturing maize varieties, AFI technique should be applied from initial stage to mid - stage (up 55 days from planting) then apply EFI at tasselling and silking stages to reduce water stress at this critical stage.

Yield and yield components of intercropped dual-purpose lablab and cowpea with maize of contrasting maturities

Intercropping is a way to intensify agricultural land use. Cowpea is an important crop in the traditional farming systems in northern Nigeria because it serves to provide food and feed. Although lablab has potential to function in these ways, it remains an underutilized crop because among other factors, there is dearth of information on its incorporation into the system by way of intercropping it with the major cereal crops. A field trial was conducted at Samaru (11o 11’N, 07o 38’E, 686 m asl) in northern Guinea savannah of Nigeria, to evaluate the relative yield and yield components of dual-purpose lablab and cowpea cultivars when gown sole and when intercropped with maize of contrasting maturities. The experiment was laid out in a split-plot design with four replications. The experiment consisted of early maize maturing cultivar (TZE COMP. 5 W) and a late maize maturing cultivar (TZL COMP. 1 SYN). Cropping system (intercropping and sole cropping) was assigned to the main plot and crop cultivar (lablab: ILRI 4612, NAPRI 2 and cowpea: IT89KD- 288, IT99K-241-2) was assigned to subplots. Results showed that intercropping cowpea or lablab into early maturing maize cultivar was more productive than intercropping into late maturing maize cultivar for number of pods (74.4 vs. 63.9), harvest index (0.22 vs. 0.20), grain yield (575.7 vs. 441.0) and fodder yield (2075.4 vs. 1758.2) for the legumes. Lablab cultivars had superior performance than cowpea for number of pods (113.5-114.2 vs. 81.1-81.5) and fodder yield (2968.9-3042.3 vs. 1725.4-1795.9 kg ha -1 ) whereas cowpea cultivars had superior performance than lablab for harvest index (0.29 vs. 0.17) and grain yield (802.3-833.9 vs. 587.8-632.4 kg ha -1 ), meaning that both legumes have potential in providing food and feed with lablab producing more fodder and cowpea more grain. Land equivalent ratio showed that intercropping advantage was higher when lablab and cowpea were intercropped with early maturing maize cultivar (1.34, 1.24) than with late maturing maize cultivar (1.10, 1.15). It is recommended that for higher lablab or cowpea/maize productivity in an intercrop, farmers should intercrop dual-purpose cultivars of these crops with maize of earlier maturities. Keywords: maize, lablab, cowpea, grain yield, fodder yield

English

This study was carried out to evaluate and assess the phenotypic correlation between the primary and secondary weevil resistant traits of 20 drought tolerant (DT) late maturing maize hybrids (LHYB) to weevil (Sitophilus zeamais Motschulsky) damage. Well-conditioned experimental samples with uniform grain moisture content were infested with 32; 10 to 14 day old weevils in the controlled temperature and humidity (CTH) environment for 55 days. Data were collected on kernel volume (KV) and grain hardness (GH) at the start of the experiment, percent weevil mortality (%WM) at the 21st day and percent grain weight loss (%GWL) and F1 weevil progeny emergence (F1WPE) at the 55th day of oviposition. Data were collected on starch, oil and protein content to confer resistance to weevil damage. There were highly significant differences (P<0.001) in F1WPE and %GWL, (P<0, 01) in KV while no significant differences were observed for %WM and GH. The obtained data confirmed that, there was a positive and significant correlation between F1WPE and %GWL, while a negative and significant correlation was observed between F1WPE and %WM. Hybrids CZH131022, CZH131003, CZH132064, CZH132069 and CZH132068 were the top five weevil resistant while hybrids CZH132066, CZH132065, CZH132074, CZH131008 and CZH132063 were the top five most susceptible. Key words: Controlled temperature and humidity, late maturing maize hybrids, Sitophilus zeamais.

Indentifying farmers’ preferences and constraints to maize production in two agro-ecological zones in Burkina Faso

The low adoption of technologies, developed by research institutions, by farmers substantiates the need for client orientation in research and development. Hence, to bridge the gap between breeders and farmers and to ensure that new varieties fit farmers’ preferences and suit their socioeconomic situations, Participatory Rural Appraisals (PRA) were undertaken in two agro-ecological zones (North-Sudan and South-Sudan) to determine maize varieties farmers grow, farmers’ preferences in choice of the varieties and to evaluate farmers’ perceptions of constraints to maize production. Farmers grow both local and improved varieties to meet their multiple objectives in maize farming. Nearly 63 % of the farmers grow local maize varieties whilst about 37 % grow improved varieties. All the different varieties are grown in both northern and southern zones but, in general, early maturing maize varieties are grown in northern zones while late maturing maize varieties are planted in southern zones. This study revealed that farmers preferred varieties that carry traits like high yield potential, early maturity, tolerance to drought, Striga and low soil fertility in all districts. Maize production in the two zones is constrained by a variety of related factors, the extent of contribution of each factor varies across the districts. The main constraints to maize production are poor cash flow, inadequate farm tools, poor extension service, drought and pests. Striga is considered as the most important pest followed by termites. Few studies have been conducted on models on Burkina Faso agriculture and technology adoption. This study identified agro-ecological zones and others key factors in adoption decision of new maize variety. It is expected that future studies will include these factors as some of the explanatory variables in adoption models.

Assessment of factors influencing the biomethane yield of maize silages

A large set of maize silage samples was produced to assess the major traits influencing the biomethane production of this crop. The biomass yield, the volatile solids contents and the biochemical methane potential (BMP) were measured to calculate the biomethane yield per hectare (average=7266m(3)ha(-1)). The most influential factor controlling the biomethane yield was the cropping environment. The biomass yield had more impact than the anaerobic digestibility. Nevertheless, the anaerobic digestibility of maize silages was negatively affected by high VS content in mature maize. Late maturing maize varieties produced high biomass yield with high digestibility resulting in high biomethane yield per hectare. The BMP was predicted with good accuracy using solely the VS content.

Genetic interrelationships among medium to late maturing tropical maize inbred lines using selected SSR markers

Understanding the genetic relationships among breeding lines is fundamental in crop improvement programs. The objectives of this study were to apply selected polymorphic single sequence repeat (SSR) DNA markers and cluster medium to late maturing tropical elite maize inbred lines for effective hybrid breeding. Twenty elite inbred lines were genotyped with 20 SSR markers. The analysis detected a total of 108 alleles. The unweighted pair group method with arithmetic mean allocated the inbred lines into five clusters consistent with the known pedigrees. The tested inbred lines that were adapted to mid-altitude, sub-humid agro-ecologies were classified in different clusters, except for a few discrepancies. The greatest genetic distance was identified between the clusters of lines CML-202 and Gibe-1-91-1-1-1-1. The analysis determined the genetic grouping present in the source population, which will assist in effective utilization of the lines in tropical hybrid maize breeding programs to exploit heterosis.

An Assessment of the Adaptability to Climate Change of Commercially Available Maize Varieties in Zimbabwe

A study was undertaken to assess the adaptability to climate change of commercially available maize varieties in Zimbabwe using 2010, 2020, 2050 and 2080 climate change scenarios. The FAO’s Ecocrop Model was used to assess the suitability of early, short, medium and long season maize varieties grown under rainfed conditions in different agro-ecological regions (1 to 5) whose agricultural potential decreases progressively due to the amount of rainfall received. Regions 1 and 2 conditions are projected to decrease in size by 14%, region 3 by 26%, while regions 4 and 5 are projected to increase by 40%. The area suitable for growing early low yielding maize varieties will remain at nearly 100% in regions 1 and 2. The area suitable for growing medium maturing varieties will decline to below 20% in regions 4 and 5. Overall, only 2% of Zimbabwe s’ land area, mainly in region 1, will be suitable for growing high yielding late maturing maize varieties. The paper concludes that the currently available maize germplasm in the country is not suitable for the projected climate change conditions.

Combining Ability and Heterosis for Yield and Quantitative Traits in Maize, Zea mays (L.)

Combining ability analysis was conducted in late maturing maize (Zea mays L.) inbred lines for yield attributes. Both additive and non additive gene effects were present in the material under study. Variance due to gca was preponderant for days to 50% pollen shedding, days to 50% silk emergence, plant height, ear height, number of kernel rows, number of kernels per row and grain yield indicating importance of additive genes in controlling the traits. Three lines KML-70, KML-223 and KML-286 and two testers, KML-36 and KML-226 were good general combiners for grain yield. The crosses KML-57 x KML-226, KML-70 x KML-3, KML-70 x KML-29 and KML-286 x KML-29 are desirable with significant positive sca, heterosis and high mean values for grain yield. KML-223 x KML-3 recorded significant negative heterosis for days to 75 per cent dry husk, combined with significant negative sca and low mean performance. Hence, this hybrid could be suitable for medium maturity situations.

Determination of combining abilities and heterotic patterns of fourteen medium to late maturing Iranian maize inbred lines using diallel mating design

Information about how elite maize (Zea mays L.) inbreds of different pedigree sources combine and perform in hybrid combinations will facilitate the selection of parents and breeding strategies for hybrid development. Fourteen medium to late maturing maize inbred lines, derived from the most commonly used source materials in maize breeding programs in Iran, were crossed in a diallel mating design. The 91 F1 hybrids and the 14 parental lines were evaluated during two years at four locations in Iran for investigation of combining abilities and to determine heterotic patterns among germplasm sources, using a biplot diallel analysis. The graphical representation offered by biplot analysis allowed a rapid and effective overview of general combining ability (GCA) and specific combining ability (SCA) effects of the inbred lines, their performance in crosses, as well as grouping patterns of similar genotypes. GCA and SCA effects were significant for grain yield (GY), number of kernel row per ear (RE), kernel number per row (KR) and thousand-kernel weight (TKW). Based on significant positive GCA effects, the lines derived from LSC could be used as parent in crosses to increase GY, KR, and TKW. The maximum best-parent heterosis values and high SCA effects resulted from crosses B73 × MO17 and A679 × MO17 for GY; K3640/5× K19/1 for TKW; K3653/2 × MO17, B73 × MO17 and A679 × MO17 for KR; and B73 × K3640/5 for RE. The best heterotic patterns were LSC × RYD, LSC × SYN L. and RYD × SYN L., which would be potentially useful in maize breeding programs to obtain high-yielding hybrids in the same climate of Iran. Key words: Maize (Zea mays L.), heterotic pattern, biplot diallel analysis, general combining ability, specific combining ability, heterosis.

Population parameters for resistance to Fusarium graminearum and Fusarium verticillioides ear rot among large sets of early, mid-late and late maturing European maize (Zea mays L.) inbred lines

Infection of maize ears with Fusarium graminearum (FG) and Fusarium verticillioides (FV) reduces yield and quality by mycotoxin contamination. Breeding and growing varieties resistant to both Fusarium spp. is the best alternative to minimize problems. The objectives of our study were to draw conclusions on breeding for ear rot resistance by estimating variance components, heritabilities and correlations between resistances to FV and FG severity and to investigate different inoculation methods. In 2007 and 2008, three maturity groups (early, mid-late, late) each comprising about 150 inbred lines were tested in Germany, France, Italy, and Hungary according to their maturity group. They were silk channel inoculated by FG (early) and FV (all groups). In the late maturity group, additionally kernel inoculation was applied in a separate trial. The percentage of mycelium coverage on the ear was rated at harvest (0-100%). Significant (P < 0.01) genotypic variances of ear rot severity were found in all groups. Inoculation was superior to natural infection because of higher disease severities and heritabilities. In early maturing flints and dents, FG caused significantly (P < 0.01) higher ear rot severity than FV (61.7 and 55.1% FG vs. 18.2 and 11.1% FV ear rot severity, respectively). FV inoculation in Southern Europe (mid-late, late) resulted in similar means between 10.3 and 14.0%. Selection is complicated by significant (P < 0.01) genotype x environment interactions. Correlation between FG and FV severity was moderate in flints and dents (r = 0.59 and 0.49, respectively) but lines resistant to both fungi exist. We conclude that chances for selecting improved European elite maize material within the existing germplasms is promising by multi-environmental inoculation trials.

Influence of nitrogen fertilization on the performance of early and late maturing maize varieties under natural infestation with Striga hermonthica (Del.) Benth

Field studies were conducted in northeast Nigeria to evaluate the response of early and late-maturing maize varieties infested with natural populations of Striga to different rates of nitrogen (N) fertilizer. There were significant reductions in the number of emerged Striga at 120 kg N ha−1 for the early varieties and at 60 and 120 kg N ha−1 for the late varieties. The number of emerged Striga only significantly differed among the late varieties. Averaged across varieties, grain yield of the early varieties was 144% higher at 60 kg N ha−1 and 192% higher at 120 kg N ha−1 than without added N. For the late varieties the increase in grain yield was 85% higher at 60 kg N ha−1 and 144% higher at 120 kg N ha−1 than without added N. Among the early varieties, TZE COMP4 C3 had significantly lower grain yield than the other varieties. Among the late varieties, grain yields of 8338-1-1 and TZB-SR were significantly lower than in the other varieties. Our results show that the application of 60–120 kg N/ha to Striga resistant or tolerant varieties may reduce damage and increase grain yield. Higher economic rates of return was obtained at N rates of 60–120 kg N/ha than the other rates.

Daily changes in the water content of early and late maturing grain maize varieties in the later stages of over-ripening

The water content of the grain, the cob and the internode below the ear, and the thousand-kernel mass of early (Mv 251, Ipoly) and late (Tisza, Mv 500) maize varieties were recorded three times a day between 7 and 17 November 2006.No daily drying was observed in the moisture content of the kernels, cobs or ear stalks. The only exception was the internode below the ear, which tended to dry gradually. Although significant differences were found between the varieties, these probably developed prior to the testing period, and did not change to any great extent during the measurements. From the point of view of harvest date, no substantial change can be expected in the equilibrium water content reached for each variety at different moisture levels, so it is unlikely that savings can be made on drying costs.

Maize silage and winter crop options to maximise drymatter and energy for NZ dairy systems

Trade-offs in dry matter (DM) and metabolisable energy (ME) between combinations of three maize silage hybrids varying in maturity from 100-113 CRM and six winter forage options were investigated in a Waikato farmer's field over 2 years. Winter crops were triticale, cut once; oats grazed 1-2 times; and Tama and Feast II Italian ryegrass, each cut or grazed 2-3 times. Greatest DM and ME production (38.9 t/ha; 396 GJ/ha) was from a 113 CRM hybrid followed by a single-cut triticale crop. The most economical sources of DM and ME were obtained from a 100 CRM maize hybrid plus grazed oats (11.8 c/ kg; 1.12 c/MJ), while the cheapest ME source among cut winter forages was a 113 CRM maize hybrid + triticale (1.18 c/MJ). Reliable annual silage production of 30 t DM/ha and 330 GJ ME/ha (or 3000 kg MS/ha) is possible using a late maturing maize hybrid combined with a winter forage crop such as triticale, although the low feed value of the triticale may limit its use as feed for milking cows. Keywords: Italian ryegrass, oats, maize silage, supplements, triticale, winter forage crops

Use of SSR data to determine relationships and potential heterotic groupings within medium to late maturing Iranian maize inbred lines

Information on germplasm diversity and relationships among elite materials is fundamentally important in crop improvement. The main objectives of our study were to: (1) determine the level of genetic diversity within and relationships among the most commonly used medium to late maturing Iranian maize inbred lines using simple sequence repeat (SSR) markers, and to (2) suggest heterotic groups among the lines using genetic distance as measured by the SSR markers. Fifty-six inbred lines, which are the most commonly used in maize breeding programs in Iran, and two lines from CIMMYT, Mexico (used as checks) were fingerprinted with 46 SSR markers. A total of 225 alleles were detected. The UPGMA clustering grouped the Iranian inbreds into four clusters (in addition to one group which included only the CIMMYT control lines), which were consistent with the pedigrees or known information about source materials. The highest distance was found between the cluster of Reid Yellow Dent related lines and the cluster of Lancaster Sure Crop related lines, and this pattern has produced some of the highest yielding hybrids in Iran. Other heterotic patterns based on the SSR markers are suggested, but must be field tested to confirm what appears to be promising alternative heterotic patterns.

Contribution made by the maize variety Mindszentpusztai Yellow Dent (MYD) to the birth of hybrid maize in Hungary and in Europe as a whole Review

The gene pool available for maize breeding is restricted. The heterosis sources used successfully over the last 80 years (Lancaster, Reid Yellow Dent) have been over-exploited and are near exhaustion (Duvick and Cassman 1999). Among the European sources of heterosis, European Flint is widely known, but its earliness and special suitability for silage maize breeding do not allow it to make any great contribution to further improvements in the yield potential of mid-season or late-maturing maize hybrids. In addition to developing new heterosis sources, the utilisation of older but little known sources could be a useful way of supplementing widely used sources. Over the last 50–60 years at least 29 inbred lines with commercial value have been developed from the Rumai group of the Central European Dent race and at least 19 from Mindszentpusztai Yellow Dent. Lines of Rumai and Mindszentpusztai Yellow Dent are at least as important in the European Corn Belt as lines originating from Lancaster Surecrop and Reid Yellow Dent are in the North American Corn Belt. In addition the first maize hybrid registered in Europe, Mv 5, was developed in Hungary, was a double cross involving three MYD lines. The paper provides a review of the contribution made by Mindszentpusztai Yellow Dent to Hungarian hybrid maize breeding during a period of over 50 years.

Stochastic use of the LEACHN model to forecast nitrate leaching in different maize cropping systems

This paper proposes a stochastic application of a deterministic model (LEACHN) with the aim of forecasting the probability of exceeding given nitrate leaching levels for different cropping systems and soil hydrological characteristics. The understanding of the level of probability associated to the prediction of leaching is an important criteria for the judgement of cropping systems. After calibration of organic matter mineralization and nitrification rates in both a sandy-loam and a loamy soil of the Western Po river valley (Northern Italy), LEACHN was used as a stochastic tool to evaluate the meteorological variability and the spatial variability of hydrological parameters of a soil. Meteorological variability was generated using series of measured air temperature, rainfall and global radiation for a period of at least 15 years, and these were then expanded to 100 years using the climate simulator CLIMGEN. Soil variability was simulated using the scale factor approach. The scale factor mean and standard deviation were obtained in eight locations within a 1000-m 2 area. The stochastic scale factors were applied to parameters a and b in Campbell’s water retention function and to hydraulic conductivity. The following combinations of crops were simulated in the two soils: (a) continuous maize for silage (MM); (b) continuous maize for grain (MG); (c) a combination of late harvested Italian ryegrass and short cycle silage maize (LRM); and (d) early harvested Italian ryegrass and late maturing silage maize (ERM). The crops were fertilized with 200 or 300 kg N ha −1 year −1 (or 450 kg for MM) and submitted to three water regimes: no irrigation, irrigation on the basis of water balance and conventional irrigation, which resulted in the highest volume. The simulated leaching was higher when fertilization and irrigation inputs were higher. It was further reduced by the introduction of cover-crop and was higher in the sandy soil. All these factors interacted, creating different levels of nitrate loss risk, that ranged from a minimum leaching of 4 kg N ha −1 year −1, with a 10% breakthrough probability of 16 kg N ha −1 year −1 (low fertilized and irrigated ERM in the sandy-loam soil) to a maximum average leaching of 146 kg N ha −1 year −1 with a 10% breakthrough probability of 235 kg N ha −1 year −1 (high fertilized, conventionally irrigated MM in the sandy soil). The breakthrough probability curves associated to nitrate leaching are skewed, showing that lower than average values are more frequent than higher ones. The standard deviations of yearly leaching were closely correlated to the means and were frequently greater than the means, particularly in the sandy soil. The stochastic simulation results offered the possibility of ranking cropping systems into classes of probability of exceeding a given value of leaching and the possibility of deriving suggestions for improved crop management.

Studies on performance of some open-pollinated maize cultivars in the Guinea savanna. III. Nitrogenuse efficiencies of four cultivars

Nitrogen use efficiency (NUE), defined as grain produced per unit of fertilizer nitrogen (N) applied, is a highly desirable agronomic character of non-leguminous crop varieties. This study was conducted to compare the NUEs of one local maize (Zea mays L.) variety and three improved composites released in Ghana since 1972, and determine the effects of breeding for improved agronomic performance on the NUEs of the improved cultivars. The four late-maturing maize cultivars (local, Composite 4,Dobidi, and Okomasa) were evaluated at 0, 80, and 160 kg N ha-1 and under three plant densities at Nyankpala and Damongo in 1992 and 1993. Across environment analysis for grain yield showed environment, plant density, nitrogen, and cultivar effects were significant (P Ghana Jnl.agric. Sci Vol.32(1), 1999: 19-26