Affects Maize Grain Research Articles

Optimal rate of nitrogen fertilizer improves maize grain yield by delaying the senescence of ear leaves and thereby altering their nitrogen remobilization

ContextNitrogen fertilization affects maize grain yield through regulating ear leaf senescence and nitrogen remobilization (RemN), yet few studies focus on how nitrogen alters the onset of leaf senescence and then affects leaf RemN to regulate grain-filling. ObjectiveThis study aimed to investigate the relationship between the onset of ear leaf senescence, ear leaf RemN, and grain-filling. MethodsA field experiment in Yancheng, China,with six nitrogen rates (0, 67.5, 136.5, 205.5, 274.5, and 343.5 kg N ha−1) were conducted and ear leaf senescence and grain-filling were analyzed in response to different N fertilizations. ResultsOptimal nitrogen fertilization (around 205.5 kg N ha−1) significantly increased grain yield (average 10359.2 kg ha−1) and harvest index (HI, average 0.58). Additionally, nitrogen application increased the nitrogen concentration of ear leaves and delayed senescence. The maximum delay was 3.4 days compared to the control. At the time of maximum grain yield, the onset of senescence could be delayed by 1.6–1.9 days. However, delayed senescence of ear leaves negatively impacted leaf RemN contribution to grain nitrogen, with a maximum limit of 16.0 observed at 205.5 kg N ha−1. Furthermore, nitrogen fertilization could reduce the maximum grain-filling rate (Gmax), the maximum grain weight (Wmax), and the time to reach the maximum grain-filling rate (Tmax). Higher grain yield and its response to nitrogen relied on a shorter time interval between the onset of senescence and Tmax. At a nitrogen fertilization rate of 196.85 kg N ha−1 (close to the optimal rate of 205.5 kg N ha−1), the minimum time interval could be reduced to about 2.4 days, resulting in a maximum relative yield response to nitrogen of 39.98%. Conclusion and implicationOptimal nitrogen fertilization improved grain yield by delaying the onset of senescence of ear leaves and altering its RemN, thus impacting grain filling. It provided valuable insights for achieving higher yields under the optimal nitrogen fertilization by considering the onset of ear leaf senescence, the ability of RemN in relation to grain filling.

Nitrogen application affects maize grain filling by regulating grain water relations

Grain water relations play an important role in grain filling in maize. The study aimed to gain a clear understanding of the changes in grain dry weight and water relations in maize grains by using hybrids with contrasting nitrogen efficiencies under differing nitrogen levels. The objectives were: 1) to understand the changes in dry matter and percent moisture content (MC) during grain development in response to different nitrogen application rates and 2) to determine whether nitrogen application affects grain filling by regulating grain water relations. Two maize hybrids, high N-efficient Zhenghong 311 (ZH311) and low N-efficient Xianyu 508 (XY508), were grown in the field under four levels of N fertilizer: 0, 150, 300, and 450 kg N ha–1 during three growing seasons. Dry weight, percent MC and water content (WC) of basal–middle and apical grains were investigated. The difference in the maximum WC and filling duration of basal–middle and apical grains in maize ears resulted in a significant difference in final grain weight. Grain position markedly influenced grain drying down; specifically, the drying down rate of apical grains was faster than that of basal–middle grains. Genotype and grain position both influenced the impact of nitrogen application rate on grain filling and drying down. Nitrogen rate determined the maximum grain WC and percent MC loss rate in the middle and the late grain-filling stages, thus affecting final grain weight. The use of high N-efficient hybrids, combined with the reduction of nitrogen application rate, can coordinate basal–middle and apical grain drying down to ensure yield. This management strategy could lead to a win–win situation in which the maximum maize yield, efficient mechanical harvest and environmental safety are all achieved.

Effects of fertilizer under different dripline spacings on summer maize in northern China

Maximizing grain yields with effective fertilization technologies and minimizing nitrogen losses is essential in agroecosystems. In this research, we conducted a two-year field experiment to explore whether dripline spacing and fertilization rate would affect maize grain yield. Two dripline spacings (i.e., one drip line per row of maize with a row space of 60 cm and one drip line per two rows of maize) and two fertilization rates (i.e., high fertilization level: N, 180 kg ha−1; P2O5, 90 kg ha−1; and K2O, 90 kg ha−1 and low level: N, 139.5 kg ha−1; P2O5, 76.5 kg ha−1; and K2O, 76.5 kg ha−1) were employed in this research. The results showed that maize yield was significantly affected by both dripline spacing and fertilization rate. The maize yield was 10.2% higher in the treatment with one drip line per two rows than that in the treatment with one drip line per row. Maize yield increased by 10.9% at the high fertilization level compared to that at the low fertilization level. The quantity of cumulative ammonia volatilization was reduced by 15.1% with one drip line per two rows compared to that with one drip line per row, whereas it increased by 26.9% at the high fertilization level compared with that at the low fertilization level. These results indicated that one drip line per two rows with a high fertilization rate increased the yield and could reduce the environmental burden, which may be economically beneficial and environmentally sound for maize fertigation for green agricultural development.

Improved nutrition and resilience will make conservation agriculture more attractive for Zambian smallholder farmers

AbstractFood and nutrition insecurity in southern Africa call for improvements in traditional agriculture systems. Conservation Agriculture (CA) based on minimum soil disturbance, permanent soil cover and crop diversification has been implemented as a strategy to maintain yields while safeguarding the environment. However, less focus has been placed on potential synergistic benefits on nutrition security. Maize-based systems may increase household income through selling but may not lead to proportionate reduction in malnutrition. Crop diversification in CA systems can have a direct impact on the nutritional status of farm households due to improved dietary diversity. Here we assess how the integration of grain legumes, cowpeas and soybeans, in maize-based CA systems either as intercrops or rotational crops affects maize grain yield and stability, total energy yield, protein yield and surplus calories after satisfying the daily requirement per household. The experiments were carried out from 2012 to 2020 (nine consecutive cropping seasons) in six eastern Zambian on-farm communities using 966 observations. Results show that intercropping compromises maize yields with marginal yield penalties of −5% compared to no-till monocropping. However, intercropped yields were more stable across environments. Total system caloric energy and protein yield were highest in intercropping systems due to higher productivity per unit land area owing to the additive contribution of both maize and legumes. Total system caloric energy and protein yield reached yearly averages of 60 GJ ha−1 and 517 kg ha−1, respectively, for the intercropping system as compared to 48 GJ ha−1 and 263 kg ha−1 in monocropped maize systems. Tillage-based monocrop resulted in the least stable yields. Our results suggest that intercropping maize with grain legumes in CA systems is a promising option for smallholder farming households to improve dietary diversity, dietary quality and stability of yields thus contributing to sustainable agriculture intensification while maintaining food and nutrition security.

Nitrogen fertilization affects maize grain yield through regulating nitrogen uptake, radiation and water use efficiency, photosynthesis and root distribution.

High external nitrogen (N) inputs can maximize maize yield but can cause a subsequent reduction in N use efficiency (NUE). Thus, it is necessary to identify the minimum effective N fertilizer input that does not affect maize grain yield (GY) and to investigate the photosynthetic and root system consequences of this optimal dose. We conducted a 4-year field experiment from 2014 to 2017 with four N application rates: 300 (N300), 225 (N225), 150 (N150), and 0 Kg ha−1 (N0) in the Northwest of China. GY was assessed by measuring the photosynthetic capacity and root system (root volume, surface area, length density and distribution). Grain yield decreased by −3%, 7.7%, and 21.9% when the N application rates decreased by 25%, 50%, and 100% from 300 Kg ha−1. We found that yield reduction driven by N reduction was primarily due to decreased radiation use efficiency (RUE) and WUE instead of intercepted photosynthetically active radiation and evapotranspiration. In the N225 treatment, GY, WUE, and RUE were not significantly reduced, or in some cases, were greater than those of the N300 treatment. This pattern was also observed with relevant photosynthetic and root attributes (i.e., high net photosynthetic rate, stomatal conductance, and root weight, as well as deep root distribution). Our results suggest that application of N at 225 Kg ha−1 can increased yield by improving the RUE, WUE, and NUE in semi-arid regions.

Can different soil fertilization regimes modify soil fauna to interfere in maize grain yield?

Soil fauna activities transform the soil, but soil organisms are also influenced by changes in the land. We hypothesize that different soil fertilization regimes modify soil fauna and in this way affect maize grain yield. The aim of this study was to evaluate the effects of different soil fertilization regimes on the structure of the soil fauna and the association between these organisms and the maize grain yield. The experiment was conducted in Maranhão State (Brazil), in an alley crop system which was divided into 32 plots of 4×10 m, with four replicates and the following treatments: Gliricidia sepium – gliricidia (G), potassium (K), humic acid (HA), humic acid + potassium (HA + K), potassium + gliricidia (K + G), humic acid + potassium + gliricidia (HA + K + G), humic acid + gliricidia (HA + G) and uncovered soil (US). Soil fauna dominance, abundance, richness, Shannon–Wiener diversity index, and Pielou evenness index and maize grain yield were determined. Fertilization with humic acid and potassium caused the dominance of isopods. The dominance of ants was also related to soil potassium (K treatment). The only taxon associated with yield was Araneae. Although fauna abundance did not show differences between treatments, it was related to yield. This study does not confirm the hypothesis that different soil fertilization regimes affect soil fauna and consequently influence maize grain yield. Nevertheless, we confirm that maize grain yield may be improved by the presence of specific groups and by the increased abundance of soil fauna.

Maize relay intercropping with fodder crops for small-scale farmers in central Brazil

AbstractRelay intercropping of maize with fodder crops is a promising option for sustainable intensification of dairy small-scale farms in the Cerrado of Brazil. Twenty-six intercropping trials were conducted on farmers’ fields with the following experimental treatments: sole maize crop cropping (MS), maize-Brachiaria intercropping (MB) and maize-pigeon pea intercropping (MP). The trials were managed by the farmers, i.e. choice of conventional tillage (CT) versus no-tillage (NT), sowing dates, fertilization and weed control. Maize grain yield varied strongly across the farmer fields, from 100 to 5900 kg ha−1 in the MS treatment, 500 to 6900 kg ha−1 in MP and 300 to 5500 kg ha−1 in MB. Intercropping did not significantly affect maize grain yields under NT, but yields were reduced under CT in one out of two seasons. Maize yields in the intercropped systems were also higher under NT than CT. Total biomass productivity was significantly higher in the maize-fodder than in the sole maize system. An increased interval between sowing of maize and fodder crop significantly reduced the fodder crop biomass. Relay intercropping, especially in combination with NT, is a promising option if crop calendars and fertilization are properly managed by farmers to reduce interspecific competition between the maize and fodder crop.

Straw Incorporation Management Affects Maize Grain Yield through Regulating Nitrogen Uptake, Water Use Efficiency, and Root Distribution

Returning crop straw to soil can potentially improve soil health and crop production, facilitating sustainable agriculture. However, the effects of straw incorporation with various tillage management techniques combined with nitrogen (N) regimes on crop root growth, and water and N utility are not well understood. In this study, rotary tillage (RTS) and plow tillage (PTS) for straw incorporation combined with N regimes (CK, no N applied; LN, 112 kg N ha−1; MN, 187 kg N ha−1; and HN, 262 kg N ha−1) were used to determine their effects on soil water and mineral N availability, root distribution, crop N uptake, grain yield, and water use efficiency (WUE) of maize in northeast China. The results demonstrate that higher levels of pre-sowing soil-water storage and field evapotranspiration (ET), and lower levels of WUE and pre-sowing soil mineral N storage (Nmin-PS) at a depth of 0–60 cm were obtained with the RTS treatments as compared to the PTS treatments. N addition improved Nmin-PS and post-harvest soil mineral N storage (Nmin-PH) at a depth of 60–100 cm in 2016, and increased WUE compared to CK. RTS treatments enhanced root weight density (RWD) at a depth of 0–60 cm in 2016–2017, root length density (RLD), ratio of root length density (RLDR), and ratio of root weight density (RWDR) at a depth of 30–60 cm in 2016, and RLD at a depth of 0–30 cm in 2017. N addition promoted RLD and RWD at a depth of 0–10 cm in 2016–2017. RTS treatments reduced pre-silking shoot N uptake (NPS) and grain yield. Shoot N uptake and grain yield were enhanced in response to increasing levels of N; however, the grain yield did not show further significant improvements when the amount of N applied was over 187 kg N ha−1 (except for RTS in 2016). Overall, tillage with straw incorporation management and N levels markedly affected the soil physicochemical properties (such as ET, Nmin-PS, and Nmin-PH). This influenced grain yield indirectly by further mediating root traits (RLD, RWD, RLDR, and RWDR) with consequences for the NPS and post-silking shoot N uptake (NPOS) of maize, which were found to have greatest direct and positive impact on maize grain yield.

Homozygosis of Bt locus increases Bt protein expression and the control of Spodoptera frugiperda (Lepidoptera: Noctuidae) in maize hybrids

Spodoptera frugiperda (J.E. Smith) is the main pest of maize in Brazil and its control has been targeted by Bt maize hybrids. Generally, Bt maize hybrids possess the transgenic locus in a hemizygous condition, that is, containing only one copy of the Bt allele. However, studies have shown that maize hybrids with an additional transgenic allele, namely, in a homozygous state, increases transgenic protein expression. Our aim in this study was to evaluate whether the transgenic event TC1507 x MON89034 x NK603 in homozygosis increases Bt protein expression levels and, consequently, reduces S. frugiperda leaf-feeding injury and larval survival which affects maize grain yield. Leaf-feeding injury of S. frugiperda was 29% lower on homozygous hybrids relative to their isogenic hemizygous versions. Isogenic homozygous and hemizygous hybrids did not differ in grain yield in this study. S.frugiperda survivorship on homozygous hybrids was significantly lower than on their hemizygous isogenic versions (16.9% and 38.5%, respectively). Homozygous hybrids presented higher Cry1F, Cry1A.105, and Cry2Ab2 protein expression levels relative to their isogenic hemizygous versions (approximately 1.5-, 2.0-, and 2.5-fold, respectively). The Bt maize event TC1507 x MON89034 x NK603 in a homozygous state increases Bt protein expression levels and the control of S. frugiperda. Therefore, the deployment of homozygous transgenic maize hybrids to farmers is more desirable than the hemizygous versions.

Correlation and path coefficient analysis for grain yield and its attributing traits of maize inbred lines (Zea mays L.) under heat stress condition

Heat stress during the flowering, pollination and grain filling periods affect maize grain yield and its attributing traits. Twenty maize inbred lines were evaluated in alpha lattice design with two replications under heat condition during spring season from February to June, 2016 at Rampur, Chitwan, Nepal. Meterological data showed maximum mean temperature (46.2–43.28ºC) and minimum (30.52-30.77ºC) in with relative humidity 37.05 to 49.45% inside the tunnel during in April-May which coincided with the flowering, pollination and grain filling periods. The data were analyzed statistically to study the correlation and path coefficient. The analysis of variance showed that all the lines were significantly different from each other for all traits anthesis silking interval, SPAD chlorophyll and leaf senescence, tassel blast, leaf firing, plant and ear height, leaf area index, ear per plant, cob length and diameter, number of kernel ear-1, number of kernel row-1, number of kernel row, silk receptivity, shelling percentage, thousand kernel weight and grain yield. Grain yield had positive and significant phenotypic correlation with silk receptivity, shelling percentage, cob length and diameter, number of kernel ear-1, number of kernel row-1, number of kernel row, SPAD chlorophyll, thousand kernel weight and significant and negative correlation with tassel blast, anthesis silking interval, leaf area index, leaf firing. Path analysis revealed that of thousand kernel weight, shelling percentage, number of kernel ear-1 and silk receptivity exerted maximum positive direct effect on grain yield. Therefore, selection of genotypes having maximum thousand kernel weight, shellingpercentage, silk receptivity and number of kernel ear-1 and shorter anthesis silking interval, no leaf firing and tassel blast is pre-requisite for attaining improvement in grain yield under heat stress condition.

Application of paclobutrazol affect maize grain yield by regulating root morphological and physiological characteristics under a semi-arid region

A field experiment was conducted to investigate the effects of paclobutrazol on ear characteristics and grain yield by regulating root growth and root-bleeding sap of maize crop. Seed-soaking at rate of 0 (CK1), 200 (S1), 300 (S2), and 400 (S3) mg L−1, and seed-dressing at rate of 0 (CK2), 1.5 (D1), 2.5 (D2), and 3.5 (D3) g kg−1 were used. Our results showed that paclobutrazol improved the ear characteristics and grain yield, and were consistently higher than control during 2015–2016. The average grain yield of S1, S2 and S3 were 18.9%, 61.3%, and 45.9% higher, while for D1, D2 and D3 were 20.2%, 33.3%, and 45.2%, compared to CK, respectively. Moreover, paclobutrazol-treated maize had improved root-length density (RLD), root-surface area density (RSD) and root-weight density (RWD) at most of the soil profiles (0–70 cm for seed-soaking, 0–60 cm for seed-dressing) and was attributed to enhancing the grain yield. In addition, root-activity, root-bleeding sap, root dry weight, diameter and root/shoot ratio increased by paclobutrazol, with highest values achieved in S2 and D3 treatments, across the whole growth stages in 2015–2016. Our results suggested that paclobutrazol could efficiently be used to enhance root-physiological and morphological characteristics, resulting in higher grain yield.

Ridge and furrow planting pattern optimizes canopy structure of summer maize and obtains higher grain yield

Ridge and furrow planting patterns could improve the micro-environment effectively, and ultimately affect maize grain yield. Previous studies mainly focused on planting only on ridges or in furrows aiming to improve the water and temperature conditions, while research on effects of planting in both ridges and furrows on canopy structure and photosynthetic characteristics of individual plants was relatively few. Hence, we hypothesized that planting in both ridges and furrows would (1) optimize maize canopy structure (better light conditions within canopy and delayed leaf senescence), (2) enhance individual leaf photosynthetic characteristics during grain filling, and (3) obtain higher grain yield. To test this hypothesis, we conducted ridge and furrow planting pattern experiments in 2013, 2014 and 2015 growing seasons in Shaanxi, a province in the Northwest of China. Zhengdan958, a corn cultivar planted widely across China, was grown at a density of 67500 plants ha−1. Three planting patterns were arranged as follows: the conventional planting pattern with row spacing of 60 cm (T0 as control), the ridge and furrow planting pattern with one row plants in each ridge and furrow (T1) and the ridge and furrow planting pattern with one row in a ridge and two rows in a furrow (T2). The three-year investigations found that significantly higher relative chlorophyll content and green leaf area per plant were observed in plants of furrows compared to T0 as well as those on ridges, leading to an advantage in terms of individual photosynthetic capacity for plants in furrows, while no significant differences about them in furrows were found between T1 and T2. In addition, we also found that plants in ridge and furrow planting patterns (T1 and T2) exhibited a significantly higher transmission of light to lower layers of the canopy (LT) than that of conventional planting pattern (T0), leading to better light conditions within canopy. Moreover, plants in furrows maintained significantly higher LAI during grain filling, leading to longer LAI duration in T2 planting pattern than other treatments due to more plants in furrows. The highest yield was observed for T2 planting pattern during three experimental years. Relative to control, plants in T2 treatment obtained 27.2%, 18.3% and 31.9% higher grain yield in 2013, 2014 and 2015 growing seasons, respectively. In conclusion, for the tested growing conditions, the planting pattern with one row in a ridge and two rows in a furrow (T2) optimized canopy structure (higher LT and longer duration of LAI), enhanced photosynthetic capacity per plant (higher Pn) during grain filling, and accumulated higher aboveground dry matter at physiological maturity, leading to a greater grain yield.

Soil Tillage Management Affects Maize Grain Yield by Regulating Spatial Distribution Coordination of Roots, Soil Moisture and Nitrogen Status.

The spatial distribution of the root system through the soil profile has an impact on moisture and nutrient uptake by plants, affecting growth and productivity. The spatial distribution of the roots, soil moisture, and fertility are affected by tillage practices. The combination of high soil density and the presence of a soil plow pan typically impede the growth of maize (Zea mays L.).We investigated the spatial distribution coordination of the root system, soil moisture, and N status in response to different soil tillage treatments (NT: no-tillage, RT: rotary-tillage, SS: subsoiling) and the subsequent impact on maize yield, and identify yield-increasing mechanisms and optimal soil tillage management practices. Field experiments were conducted on the Huang-Huai-Hai plain in China during 2011 and 2012. The SS and RT treatments significantly reduced soil bulk density in the top 0–20 cm layer of the soil profile, while SS significantly decreased soil bulk density in the 20–30 cm layer. Soil moisture in the 20–50 cm profile layer was significantly higher for the SS treatment compared to the RT and NT treatment. In the 0-20 cm topsoil layer, the NT treatment had higher soil moisture than the SS and RT treatments. Root length density of the SS treatment was significantly greater than density of the RT and NT treatments, as soil depth increased. Soil moisture was reduced in the soil profile where root concentration was high. SS had greater soil moisture depletion and a more concentration root system than RT and NT in deep soil. Our results suggest that the SS treatment improved the spatial distribution of root density, soil moisture and N states, thereby promoting the absorption of soil moisture and reducing N leaching via the root system in the 20–50 cm layer of the profile. Within the context of the SS treatment, a root architecture densely distributed deep into the soil profile, played a pivotal role in plants’ ability to access nutrients and water. An optimal combination of deeper deployment of roots and resource (water and N) availability was realized where the soil was prone to leaching. The correlation between the depletion of resources and distribution of patchy roots endorsed the SS tillage practice. It resulted in significantly greater post-silking biomass and grain yield compared to the RT and NT treatments, for summer maize on the Huang-Huai-Hai plain.

Evaluation of a new formulation of atrazine and metolachlor mixture for weed control in maize in Nigeria

Field studies were conducted in 2002 and 2003 at Ibadan, Nigeria, to evaluate the effects on weed control in maize of a new formulation of a mixture of atrazine and metolachlor. The treatments were the new formulation of the mixture at doses from 1.0 to 4.0 kg a.i. ha –1 and the old formulation of the mixture at the recommended dose of 2.5 kg a.i. ha –1. The new formulation of the mixture gave complete control of Panicum maximum, Commelina benghalensis, sedges ( Mariscus alternifolius, Kyllinga squamulata, and Cyperus spp.), and Tridax procumbens, and good control (>94%) of Passiflora foetida at 4 weeks after treatment (WAT) in 2002. At 8 WAT, the new mixture gave good control (>73%) of P. maximum and C. benghalensis in 2002, and of P. foetida, sedges, and T. procumbens in both years. The hoeweeded control and all herbicide treatments at 4 WAT had lower weed dry matter than the untreated control in both years, and at crop harvest in 2002. In both years, the lowest weed dry matter was obtained from the hoeweeded control at crop harvest. In 2003, the old formulation of the mixture at the recommended dose had similar weed dry matter with the new formulation at all doses. The treatments did not significantly affect maize grain yield in 2002. However, in 2003, the new formulation of the mixture at a dose of 4.0 kg a.i. ha –1 and the hoeweeded control had 33% higher maize grain yield than the untreated control. The new formulation of a mixture of atrazine and metolachlor is effective for weed control in maize at lower doses than the recommended dose of the old formulation.

Intercropping controls Striga in maize based farming systems

Intercropping maize was evaluated as a means to reduce Striga emergence and survival and improve overall farm productivity. Field experiments were conducted at two sites in western Kenya from 1996 to 1999 to study the effect of eight different intercrops on Striga populations and crop yield. Factors studied included relay or simultaneous planting of maize or intercrops, ridge and flat planting systems and in-row or between-row planting of intercrops. Mode of planting maize and intercrops (ridge/flat or in/between row planting) did not affect maize grain yield. However, ridge planting improved intercrop yields and reduced Striga densities. Peanut, bean, yellow gram, bambara nut and soybean intercrops produced considerable yields and increased the overall productivity of the cropping systems. The increase in output of farm produce ranged between 40% and 120% depending on the local agro-ecological conditions. Of the most productive intercrops, yellow gram provided the most stable Striga control over years and locations comparable only to cowpea. Peanut, bambara nut, bean and soybean were more variable in terms of Striga suppression in maize depending on the specific agro-ecological conditions. Shading, higher humidity and lower temperatures under the intercrop canopies were most likely the mechanisms which caused the decline of Striga numbers in intercropping systems. Intercropping can be an effective component of an integrated Striga control program compatible with the limited resources of small-scale subsistence farmers. In the long term, however, Striga populations can only diminish if intercropping is combined with handweeding of mature Striga plants to avoid the replenishment of the Striga seed bank in the soil.

Effect of rate and time of nitrogen fertilizer application on <i>Striga hermonthica</i> infestation in field-grown maize

The effects of urea and sulphate of ammonia applied at 0, 90, 120, 150 and 180 kg N ha-1 (from 1989 to 1992) and the time and rate of N application (1992) on the severity of Striga hermonthica infestation and maize yield were studied in order to compare the two sources of N fertilizer, commonly available to farmers in Ghana, in reducing S. hermonthica infestation, and to determine the rate and time of application that would minimise the deleterious effect of Striga on maize. The experiments were carried out under natural field infestations on farmers' fields (6-10 locations each year) in the Guinea Savanna zone of Ghana and replicated three times at each location on plots 5 m long and 3.6 m wide. In 1989 and 1992, higher S. hermonthica population density was recorded when urea was applied compared to sulphate of ammonia. However, there were no differences in Striga population density between the two sources of nitrogen from 1990 to 1991. Applying N at either 4 or 6 weeks after planting (WAP) maize did not affect the number of emerged Striga shoots. The rate of nitrogen applied did not influence the emergence of Striga from 1989 to 1991 as compared to 1992 when Striga population declined with increased rate of nitrogen fertilizer. Maize grain yield was unaffected by the source of nitrogen applied from 1989 to 1991. Similarly, applying N fertilizer at 4 or 6 WAP did not affect maize grain yield in 1992. However, the application of sulphate of ammonia resulted in higher maize yield compared to urea in 1992. Maize grain yield increased with increased nitrogen rate up to 90 kg ha-1 beyond which no appreciable increase was observed. A minimum of 90 kg N ha-1 is therefore required for any meaningful reduction in the deleterious effects of Striga on maize. In addition, to reduce the population of Striga in maize, it is essential to apply N fertilizers early. Ghana Jnl agric. Sci. Vol.30(2) 1997: 127-133

Competition between maize and Rottboellia exaltata

SUMMARYOne pot and five field experiments were made to study different aspects of the competition between R. exaltata and maize.The growth of young maize plants was not inhibited by being grown together in pots with young R. exaltata plants. In the field the soil tended to be somewhat wetter when the two species were grown together than when maize was grown alone, and was wettest with R. exaltata grown alone. Maize grain and total yield decreased and shoot yield of R. exaltata increased with R. exaltata plant density on both irrigated and unirrigated blocks of land, but yields were not much affected on either block by increase in plant density of maize or in nitrogen supply; maize yield was increased by irrigation but that of R. exaltata was not. Maize plant arrangement did not greatly affect maize grain and total yield or R. exaltata shoot yield, nor did arrangement of R. exaltata plants have much influence on their depression of maize yield, but R. exaltata caused a greater decrease in the grain yield of a short than of a tall maize cultivar.R. exaltata plants germinating at the same time as the crop plants did not have much effect on maize grain yield if they were removed by 8 weeks after the seedlings emerged, but decreased it considerably if allowed to remain for 12 weeks or more; weeds sown 2 or more weeks after the maize emerged hardly grew and had little effect on maize yield. When maize and R. exaltata were grown together leaf area of the maize was little affected up to the time of flowering, but was decreased after flowering, while leaf area of the weed was greatly depressed. Up to 7–8 weeks after seedling emergence more of the ground area was covered by foliage when maize was grown with R. exaltata than when it was grown alone, but later the ground was completely covered by foliage in both cases. Dry weight of grain and shoot of maize increased and that of shoot of R. exaltata decreased when the weed plants were shortened with growth regulators.