Above-ground Dry Matter Production Research Articles

Crescimento de frutos do meloeiro sob diferentes relações fonte: dreno

Um experimento foi realizado em ambiente protegido, de setembro de 2004 a janeiro de 2005, para avaliar o efeito da densidade de plantio e do número de frutos por planta no aumento da biomassa de frutos de meloeiro cultivado em substrato de casca de arroz crua e fertirrigado com solução nutritiva recirculada. Três densidades de plantio (1,7; 2,4 e 3,0 plantas m-2) e dois números de frutos por planta (3 e 4) foram estudados. A partir dos dados de matéria seca e fresca, aos 68 dias após o transplante, foram determinadas à produção e a distribuição de biomassa para os frutos. A matéria seca alocada nos frutos variou de 57 a 62% ao final do ciclo de cultivo, confirmando que, no meloeiro, estes são os maiores drenos de assimilados. A área foliar do meloeiro conduzido verticalmente e podado, ao final do cultivo, é relativamente baixa, o que associado a uma alta disponibilidade radiativa, evitou o excesso de sombreamento mútuo entre as plantas, mesmo na maior densidade de plantio. Assim, a maior densidade não afetou a distribuição de matéria seca e fresca para os frutos, aumentou a produção absoluta, por unidade de área, da biomassa da cultura e dos frutos. O aumento do número de frutos reduziu a matéria seca média dos frutos, sem afetar a produção e a distribuição de matéria seca total da planta e dos frutos. Entretanto, a produção e a distribuição de matéria fresca para os frutos assumem um comportamento diferente do da matéria seca, sendo ambas beneficiadas com tal incremento.

Response of a plurispecific permanent grassland to border irrigation regulated by tensiometers

To improve water use efficiency (WUE) of border irrigation, an integrated approach of tensiometric regulated irrigation that considered both crop response (yield and quality) and water losses was investigated. The study was carried out on plurispecific and permanent grasslands on a Mediterranean plain (Crau region in France) with high quality hay production. The soil water potential ( Ψ total) was used to schedule irrigation and diagnose mild water deficits. Neutron probe measurements were used to quantify the soil water deficit experienced by the plants based on the fraction of transpirable soil water (FTSW). The dynamic of above-ground dry matter production and botanic composition were analysed with reference to the FTSW. The results show the extreme sensitivity of grassland to a mild soil water deficit between two irrigation dates. Across the range of soil water deficit observed in these experiments, both hay production and botanical composition were closely related to the average FTSW. Above-ground biomass rapidly stopped increasing when the FTSW reached 60%. The botanical composition was also significantly changed by water deficits. The concordance between the soil water measurements and grassland response implies that the regulated deficit irrigation based on the soil water potential or FTSW can be used to optimize border irrigation efficiency when the trade-off between water saving and profit losses by mild water deficit is not easy to manage.

Effects of nitrogen fertilizer application rates on nitrate nitrogen distribution in saline soil in the Hai River Basin, China

Soil nitrate nitrogen (NO3 −-N) accumulation is related closely to NO3 − leaching, which is an important issue in groundwater pollution, especially in intensive agricultural areas with saline soils where volumes of water are used in irrigation to avoid salt accumulation in the root zone. However, in the saline environment in Hai River Basin, China, the importance of detailed research into NO3 −-N distribution in the root zone has not been adequately recognized. Considering the impacts of eco-environmental system N and crop production, the present study aimed at contributing to an understanding of the effects of N application rate on soil NO3 −-N distribution, NO3 −-N residue, N loss, and maize (Zea mays L.) yield in this region. The experiment was a completely one-factorial, randomized layout with 4 N application rates. Plant samples and soil samples from 0 to 100 cm depth were collected 8 and 9 times during the growing season, respectively. Soil NO3 −-N concentration was determined using a Flow Solution IV Analyzer. Soil water content was monitored throughout the season via the soil auger method. Samples of irrigation water and rainfall were collected and analyzed for total nitrogen contents. Maize (Zea mays L.) above-ground, dry matter production, grain yield, and harvest index (HI) were measured. And nitrogen content in plant samples was determined by the Kjeldahl method. Under fertilizer treatment, larger quantities of NO3 −-N were present in the upper soil layer (0–40 cm) at 7 days after fertilization (DAF). From 7 to 37 DAF, NO3 −-N decreased, obviously because of the heavy rainfall together with the increase in the capacity of maize to accumulate N in this period, and a significant decrease in NO3 −-N stock was observed. There was a significant positive correlation between the quantity of NO3 −-N stock decrease and the nitrogen fertilizer application rates during this period. And there was more NO3 −-N accumulated in the lower layers under fertilization treatment at 76 DAF. N fertilizer application also had a great effect on maize yield and the highest yield occurred under the treatment of 70 kg N ha−1. This study showed that the N application rate had a significant effect on maize yield, maybe because of the low initial NO3 −-N content. Higher N application rate increased N uptake, but it also increased NO3 −-N residue and N loss, therefore increasing the risk of NO3 −-N leaching. This study showed the present nitrate application rate (140–180 kg N ha−1) during maize cropping season was excessive in the study area. Nitrogen fertilizer application increased NO3 −-N concentration and stock in 0–100cm soil profile and changed NO3 −-N distribution during maize cropping season. And nitrogen fertilizer application promoted movement of NO3 −-N down the soil profile and increased N loss. But effects of nitrogen fertilization application rate on above-ground dry matter production and grain yield were non-linear. A strictly controlled, site-specific, long-term fertilization study will be set up for the determination of biochemical processes of soil NO3 −-N and for the effective N fertilizer management of the saline soil areas.

Modelling carbon dynamics in mixed grass–red clover swards

Growth and carbon dynamics in mixed grass–red clover leys were simulated using a growth model for pure stands based on radiation use, allocation within plant and loss of biomass. The model and its parameter values were taken from previous applications of the model to pure swards of grass and red clover grown in the same experiment at the same sites and years. The field data used comprised above-ground dry matter production and proportion of clover in a mixture of red clover ( Trifolium pratense L.), timothy ( Phleum pratense L.) and meadow fescue ( Festuca pratensis Huds.) in two seasonal growth cycles during two consecutive years, sampled at six sites in Central and Southern Sweden. On average for all fields, the proportion of clover decreased with increased nitrogen application. It increased from the first to the second cut, but decreased from the first to the second year. The model most often underestimated above-ground biomass when using proportion of clover and estimates of radiation use efficiency ( ε) and root allocation fraction ( b r) from values in the pure stands (Method 1). This discrepancy suggested that ε might be higher for the mixed stand than the pure stands. Values of ε and b r for the mixed stands were therefore derived by calibration to the observed above-ground biomass (Method 2). The radiation use efficiency ( ε) of the mixed stand was on average 6% higher than estimates of ε from pure stand values and proportion of clover. Overall, the variation in radiation use efficiency of mixed stands due to cutting and year was similar to that of pure stands of grass and clover, whereas the relationship to N treatment was weak and more similar to that of clover. The explanation that variations in biomass production were due to changes in root allocation seems reasonable. No variations in radiation use efficiency or root allocation fraction could be related to the proportion of clover. The variations due to cutting and year overwhelmed any such effect.

Post-establishment fertilization of Minnesota hybrid poplar plantations

Experimental plantings were installed at five sites in three locations in western Minnesota. Aboveground biomass production increased 43–82% as a result of three annual applications of urea or balanced nutrient blend fertilizer beginning near canopy closure. There were no production differences between the type of fertilizer used, indicating that N was the major limiting nutrient. Responses were consistent from site to site, indicating that hybrid poplar stands in this region at this stage of development would be very responsive to fertilization. Leaf tissue N, P, and K concentrations increased in response to both fertilizer treatments; P and K increased more frequently in response to the blend treatment compared to the N-only urea treatment. The diagnosis and recommendation integrated system (DRIS) indices indicated that the stands were near optimal nutritional balance prior to fertilization. Treatments increased individual leaf area and leaf litter production up to 33% and 37%, respectively. Canopy leaf area, leaf N concentration and the sum of DRIS indices were correlated with aboveground production. Growth efficiency, the ratio of production to canopy leaf area, increased with both fertilizer treatment and successive years of treatment, indicating improved stand vigor due to nutrient amendments. Stand production increased more in response to changes in leaf N concentration as stands aged. Plantation production continued to increase with increased internal N concentration even when deficiency levels or levels defined as sufficient for fast growth were exceeded. The correlation between aboveground production and the sum of DRIS indices shows that optimal nutrition at canopy closure may result in current aboveground dry matter production exceeding 13 Mg ha � 1 yr � 1 . Multiple small-dose amendments appear to be effective in increasing production by

Planting Date Effects on Winter Triticale Dry Matter and Nitrogen Accumulation

Addition of triticale (×Triticosecale Wittmack) into more diversified cropping systems could provide valuable economic and environmental benefits to producers in the U.S. Corn and Soybean Belt. To maximize triticale value, research was conducted to identify planting dates that allowed maximum dry matter production and N capture. Winter triticale was planted at 10‐d intervals from 15 September to 15 October at three Iowa locations: central, northeast, and southwest for two growing seasons: 2002–2003 and 2003–2004. Aboveground dry matter production, N concentration, and N removal were greater at southwest Iowa than central and northeast Iowa. Dry matter production decreased as planting was delayed from late September to late October. Nitrogen accumulation at any time during the spring and summer was greater for September‐ than October‐planted triticale in 2002–2003. At the end of the 2002–2003 season, mid‐September‐planted triticale had accumulated 37% more N than mid‐October‐planted triticale. In 2003–2004, total N capture occurring by early May was less for late‐October‐planted triticale than the other three planting dates, but there were no differences in N capture among the four planting dates from late May until maturity. Dry matter production was greatest when at least 300 growing degree days (GDDs) (base 4°C) accumulated between planting and 31 December. These results suggest that triticale should be planted in September to maximize spring forage yield and N accumulation although later planting dates would provide a higher quality forage if harvest was not delayed into late spring and summer.

Photosynthetic Capacity and Productivity of CO2-Enriched Rice (Oryza sativa L.) Under Field Conditions

SUMMARY We studied the impacts of free-air CO2 enrichment (FACE), and the interaction with nitrogen (N) fertilization, on the photosynthetic capacity of the flag leaf, above-ground dry matter production and grain yield of rice (Oryza sativa L.). Plant were exposed to ambient or elevated [CO2] (ambient + 200 μmol mol−1) and 4, 9 or 15 g N mr 2 . We found no evidence of down-regulation of the photosynthetic capacity of the flag leaf in FACE. Although a reduction in N fertilization reduced the content of nitrogen and photosynthetic pigments, this hardly affected the photosynthetic capacity of the flag leaf. Both FACE and N enrichment stimulated the above-ground dry matter production and grain yield, however, the stimulation of grain yield by FACE was not significant at low N supply.

Nitrogen and green foxtail (Setaria viridis) competition effects on corn growth and development

Agronomic research on the effects of nitrogen fertilizer and weed control in corn has focused primarily on maintaining or increasing yield. Few studies have examined the effect of nitrogen (N) fertilizer rate or weed competition (or both) on whole plant growth and development. The objectives of this research were to determine how N influences the growth and development of corn and to explore how green foxtail density affects this relationship. Field experiments were conducted on a sandy low organic matter soil from 1999 to 2001. The experiment was designed as a factorial with N rate ranging from 0 to 200 kg N ha−1and targeted green foxtail density ranging from 0 to 300 plants m−2. Under weed-free conditions, a higher rate of N fertilizer increased corn leaf and grain N content, leaf area index (LAI), plant height, and aboveground dry matter (DM) production, including kernel weight. However, in the presence of green foxtail, corn leaf N content, LAI, growth rate, plant height, and aboveground DM were reduced at each N level. Despite having significant main effects, there was no interaction between N rate and green foxtail density. Results indicate that in corn grown on a coarse-textured soil with low organic matter, the additional stress brought about by the presence of green foxtail exacerbated the effect of low N rates on corn growth and development. More intensive weed management may be required in corn if N fertilizer rates are reduced.

Sowing rate and cultivar affect total biomass and grain yield of spring triticale (× Triticosecale Wittmack) grown in a Mediterranean-type environment

Sowing rate and cultivar are basic management choices affecting biomass production, grain yield and forage quality of triticale, but their effect on this species has seldom been analysed through explanatory models such as grain yield=radiation intercepted (RI)×radiation use efficiency (RUE)×harvest index (HI). A 3-year field experiment was carried out in Sardinia (Italy) to explain the effect of five sowing rates (50, 100, 300, 500 and 700 germinable seeds per unit area) and of two cultivars of contrasting height on above-ground dry matter (AGDM) and grain production under both rainfed and irrigated conditions. The different sowing rates applied were effective in determining different plant numbers per unit area, although in 1994 the plant population density was lower than expected. Increasing sowing rates caused faster development, with a 1-week difference between extreme sowing rates in time to achieve double ridge and terminal spikelet. AGDM at anthesis was small or not influenced by sowing rate, due to the small differences in RI deriving from the greater LAI of the highest sowing rates (an average of 2.4 for 300, 500 and 700 versus 1.8 of 50 and 100). AGDM accumulated after anthesis increased as a consequence of increasing the sowing rate from 50 to 300, causing parallel differences in AGDM at maturity (from 1550 to 2177 g m −2 on average) and in grain yield (from 524 to 781 g m −2 on average). The greater AGDM accumulated after anthesis by 300 and 700 was due to a greater RI in 1996, but to a greater RUE in 1995, when a notable difference in sink size among sowing rates was detected. Sink size was also responsible for the higher HI observed at the highest population densities in two seasons out of three. The superiority of cultivar Rigel in AGDM production derived from its higher RUE (1.26 versus 1.04 g MJ −1 of Antares), associated with a lower specific leaf area and with a better light distribution within the canopy. The latter was a consequence of a lower radiation extinction coefficient before ear emergence (0.60 versus 0.70), and of less radiation intercepted by Rigel ears afterwards. A higher HI allowed the greater AGDM produced by Rigel to be translated into a higher grain yield in 2 years out of three, in spite of Rigel being taller. The framework used was effective in explaining the differences in AGDM and grain yield induced by the treatments applied. RUE was not affected by the different LAIs realised before anthesis, but was sensitive to variations in the sink capacity in the post-anthesis period and to differences in canopy structure between cultivars.

Change in oak to pine dominance in secondary forests may reduce shifting agriculture yields: experimental evidence from Chiapas, Mexico

In areas where fallow agriculture is practiced under increasing pressure on land, reduced soil fertility may derive not only from shorter fallow periods, but also from changes in floristic composition and structure in regenerating forest patches. The possible effects of these latter on soil fertility and subsequent crop yields has been largely neglected. The consequences of an observed shift from Quercus- (oak) to Pinus- (pine) dominated fallows on crop yields was investigated in the mountains of Chiapas, southern Mexico. Three successive crops, Zea mays L. var. praecox (popcorn), Triticum aestivum L. (common bread wheat), and a local landrace of Zea mays L. cv. “olotón amarillo” were grown in 210 pots. Growth substrates obtained from forest microsites with similar climate, fallow period and soil type, but with different combinations of litter to mineral soil ratio (LR=grams of litter/grams of both mineral soil and litter) and pine litter dominance (PLD=grams of pine litter/grams of total litter), were used, with or without litter burning. Organic matter, total N, extractable phosphorus, pH, CEC, and soil C/N ratio were analyzed in 144 randomly chosen pots. Multiple regression analysis was used to assess the relative importance of LR, PLD, and burning or non-burning of litterfall on aboveground dry matter production and on soil variables. Increase in LR generally resulted in a positive effect on soil variables and crop yields; litter burning had a statistically significant effect (P<0.01), but its favorable influence on yield was rather small. Pine dominance, as reflected in PLD, modified soil variables and reduced crop yields; its effects were relatively stronger when burning was prevented and when accumulated litter was low. Possible consequences of human-induced pine dominance on the soil resource base and on the dynamics of fallow agriculture are discussed.

Change in oak to pine dominance in secondary forests may reduce shifting agriculture yields: experimental evidence from Chiapas, Mexico

In areas where fallow agriculture is practiced under increasing pressure on land, reduced soil fertility may derive not only from shorter fallow periods, but also from changes in floristic composition and structure in regenerating forest patches. The possible effects of these latter on soil fertility and subsequent crop yields has been largely neglected. The consequences of an observed shift from Quercus- (oak) to Pinus- (pine) dominated fallows on crop yields was investigated in the mountains of Chiapas, southern Mexico. Three successive crops, Zea mays L. var. praecox (popcorn), Triticum aestivum L. (common bread wheat), and a local landrace of Zea mays L. cv. “ olotón amarillo” were grown in 210 pots. Growth substrates obtained from forest microsites with similar climate, fallow period and soil type, but with different combinations of litter to mineral soil ratio (LR=grams of litter/grams of both mineral soil and litter) and pine litter dominance (PLD=grams of pine litter/grams of total litter), were used, with or without litter burning. Organic matter, total N, extractable phosphorus, pH, CEC, and soil C/N ratio were analyzed in 144 randomly chosen pots. Multiple regression analysis was used to assess the relative importance of LR, PLD, and burning or non-burning of litterfall on aboveground dry matter production and on soil variables. Increase in LR generally resulted in a positive effect on soil variables and crop yields; litter burning had a statistically significant effect ( P<0.01), but its favorable influence on yield was rather small. Pine dominance, as reflected in PLD, modified soil variables and reduced crop yields; its effects were relatively stronger when burning was prevented and when accumulated litter was low. Possible consequences of human-induced pine dominance on the soil resource base and on the dynamics of fallow agriculture are discussed.

Response of Irrigated Acala and Pima Cotton to Nitrogen Fertilization

Acala (Gossypium hirsutum L.) and Pima (G. barbadense L.) cotton growth, lint yield, and fiber quality responses to N in the San Joaquin Valley, CA were evaluated. Numerous reasons, including adaptation of N fertilization guidelines to modern production practices, recent increases in energy costs, and growing concerns about NO−3 contamination of ground water, led to the initiation of this study. Acala was grown for 3 yr on a Panoche clay loam [fine‐loamy, mixed (calcareous), thermic Typic Torriorthents] and a Wasco sandy loam (coarse‐loamy, mixed, nonacid, thermic Typic Torriorthents). Pima was grown for 2 yr on the Panoche clay loam. Four N treatments were established in a randomized complete block design: 56, 112, 168, and 224 kg N ha−1. Three‐year average aboveground dry matter production of Acala was 7800 and 12 600 kg ha−1 on the Panoche clay loam and 8500 and 11 900 kg ha−1 on the Wasco sandy loam for the 56 and 168 kg N ha−1 treatments, respectively. The equivalent 2‐yr averages for Pima were 7600 (56 kg N ha−1) and 10 800 kg ha−1 (168 kg N ha−1). Linear increases in lint yield with increased N fertility level occurred for Acala on Panoche clay loam in every year. Maximum lint yield averaged over 3 yr was 1842 kg ha−1 in the 224 kg N ha−1 treatment. The response of Acala lint yield to N management on the Wasco sandy loam was smaller than on Panoche clay loam, with a maximum lint yield of 1666 kg ha−1 (224 kg N ha−1, 3‐yr average). Pima lint yield responded to N management in a quadratic fashion with maximum yields in the 168 kg N ha−1 treatment in both years (1638 kg ha−1, 2‐yr average). Acala gin turnouts were greater at the Panoche than at the Wasco site. Decreases in gin turnout with increasing N were significant on the Panoche clay loam (Acala and Pima) but not on the Wasco sandy loam (Acala). There was a generally positive relationship between increasing N fertilization and yield; however, efficient N management should include an assessment of available soil residual N, soil type, and yearly climatic conditions.

Variation in soybean (Glycine max (L.) Merr.) interference among common cocklebur (Xanthium strumarium L.) accessions

Common cocklebur is an annual dicotyledonous weed that is extremely competitive with agronomic crops, and known to be variable for traits such as leaf and bur morphology, biomass production, and photosynthetic rate. The purpose of this study was to determine if variability of this species was manifested in its ability to reduce soybean yield. Seven common cocklebur accessions from different regions of the United States were compared over three growing seasons at Urbana, Illinois. Plots were established with each common cocklebur accession planted between soybean rows at a density of one plant per metre of row. Averaged over all accessions, soybean yield reductions were 48% and 20% in 1999 and 2001, respectively, relative to weed-free control plots. No yield reduction by common cocklebur was observed in 2000. Accession and year, but not the year by accession interaction, were significant (P<0.05) sources of variation in the 1999 and 2001 combined ANOVA for soybean yield reduction and for aboveground common cocklebur dry matter. Averaged over 1999 and 2001, soybean yield reductions ranged from 25% to 42%, depending on the accession. The amounts by which common cocklebur accessions reduced soybean yield were highly correlated (r=0.92) with their aboveground dry matter production. Variability in soybean yield-reduction potential among common cocklebur accessions makes it more difficult to develop accurate economic thresholds for managing this weed.

Effects of spray application of urea fertilizer at stem extension on winter wheat yield

Supplying a proportion of the N requirement of a wheat crop via the foliage would potentially reduce immobilization of fertilizer N in the soil organic matter and N losses by leaching or denitrification. A field experiment was carried out at Harper Adams in Shropshire to investigate the effect on crop yield of supplying the spring N application to winter wheat as different proportions of urea as a solution rather than as conventional soil-applied urea, and to determine the physiological basis of any yield differences. A solid ammonium nitrate treatment was included to represent alternative commercial practice to solid urea. Treatments were repeated on the same plots over the 3 years 1992, 1993 and 1994. Solid fertilizer was applied as a single dressing, whereas urea sprays were split over a number of days to reduce scorch. Nitrogen as urea sprays produced similar grain yields to N applied conventionally to the soil as solid ammonium nitrate or urea, but effects on above-ground dry matter production and harvest index depended on the time of application. Application of a large proportion of N as urea sprays, such that some of the N as urea solution was applied later in relation to crop development, produced less above-ground dry matter, but compensated by increasing harvest index. It is concluded that application of N as urea sprays could be successfully used to substitute for soil-applied N fertilizer at stem extension in winter wheat without loss of yield. Extra application costs, however, are likely to outweigh any efficiency or environmental benefits, except where applications of solid N are made to dry soils.

Yield, Dry Matter Partitioning, and Storage Quality of Hardneck Garlic as Affected by Soil Amendments and Scape Removal

Two on-farm field studies were conducted in 1996 and repeated in 1997 to determine the effects of soil amendments and scape (flower stalk) removal on yield, dry matter partitioning, and storage quality of hardneck garlic (Allium sativum L.). One study site was on a loamy sand soil with low organic matter and fertility and the other site was on a sandy loam soil with high organic matter and fertility. Soil amendment treatments tested at both sites were: 1) no amendment, 2) composted manure, and 3) inorganic fertilizer according to soil test recommendations. A fourth treatment, dried, composted turkey-manure-based fertilizer, was included at the low organic matter site. Scapes were removed at the curled stage from plants in half of the harvest rows. Scapes from the remainder of the harvest row plants were allowed to mature until harvest. In 1997, bulbs from each treatment were stored at 0 to 3 °C or 19 to 21 °C for 6 months. Soil amendment treatments had no effect on total garlic bulb yield, dry mass partitioning, or stored bulb weight loss at the sandy loam, high organic matter site. Manure compost, fertilizer, and composted turkey manure soil amendments reduced the yield of smaller bulbs compared with the control at the loamy sand, low organic matter site. The proportion of bulbs &gt;5 cm was highest with the manure compost treatment. At the low organic matter site, scape removal resulted in a 15% increase in bulb yield and an increase in bulb size compared with leaving scapes on until harvest (P = 0.05). At the high organic matter site, scape removal increased bulb yield by 5% (P = 0.10). Scape removal increased dry matter partitioning to the bulbs, but had no effect on total (scape + shoot + bulb) aboveground dry matter production. The increase in bulb dry mass when scapes were removed was offset by an increase in scape dry mass when scapes were left on. Bulb weight loss in storage was less at 0 to 3 °C than 19 to 21 °C. Soil amendments only affected bulb storage quality at the loamy sand, low soil organic matter site. The effect of scape removal on bulb weight loss was nonsignificant at either location.

Water balance changes in a crop sequence with lucerne

In a detailed study of soil water storage and transport in a sequence of 1 year wheat and 4 years of lucerne, we evaluated drainage under the crop and lucerne as well as additional soil water uptake achieved by the subsequent lucerne phase. The study was performed at Wagga Wagga on a gradational clay soil between 1993 and 1998, during which there was both drought and high amounts of drainage (&gt;10% of annual rainfall) from the rotation. Lucerne removed an additional 125 mm from soil water storage compared with wheat (root-zone of ~1 m), leading to an estimated reduction in drainage to 30–50% of that of rotations comprising solely annual crops and/or pasture. This additional soil water uptake by lucerne was achieved through apparent root extension of 2–2.5 m beyond that of annual crops. It was effective in generating a sink for soil water retention that was about double that of annual crops in this soil. Successful establishment of lucerne at 30 plants/m2 in the first growing season of the pasture phase was a requirement for this root extension. Seasonal water use by lucerne tended to be similar to that of crops in the growing season between May and September, because plant water uptake was confined to the top 1 m of soil. Uptake of water from the subsoil was intermittent over a 2-year period following its successful winter establishment. In each of 2 annual periods, uptake below 1 m soil depth began late in the growing season and terminated in the following autumn. Above-ground dry matter production of lucerne was lower than that by crops grown in the region despite an off-season growth component that was absent under fallow conditions following cropping. This apparent lower productivity of lucerne could be traced in part to greater allocation of assimilate to roots and also to late peak growth rates at high temperatures, which incurred a penalty in terms of lower transpiration efficiency. The shortfall in herbage production by lucerne was offset with the provision of timely, high quality fodder during summer and autumn. Lucerne conferred indirect benefits through nitrogen supply and weed control. Benefits and penalties to the agronomy and hydrology of phase farming systems with lucerne are discussed.

Corn yield and fertilizer N recovery in water-table-controlled corn–rye-grass systems

Concern about NO − 3 leaching and groundwater pollution from corn monoculture has prompted an investigation of alternative production systems that reduce leaching. It is hypothesized that both intercropping and water-table control could increase N uptake and reduce the quantity of N that might be lost due to leaching. This study compared corn ( Zea mays L.) with annual Italian rye-grass ( Lolium multiflorum Lam) intercropping and corn monocrop systems under three controlled drainage levels [free drainage (water table 1 m below soil surface), and water-table depths maintained at 0.70 or 0.80 m, below the soil surface via subirrigation]. Annual Italian rye-grass was planted 10 days after the corn was planted. Grain yield, above-ground dry-matter production, N uptake and fertilizer N recovery (FNR) were assessed over 2 years on a fine, silty, mixed, non-acid, frigid Typic Humaquept sandy loam soil. Corn grain yields were unaffected by the annual rye-grass/weed component of the intercropping system or the various water-table depths in either year. Intercropping increased the total above-ground dry-matter production by 3.2 and 2.4 Mg ha −1 and N uptake by 71 and 49 kg ha −1 in 1993 and 1994, respectively. Fertilizer N recovery from corn was not different between the two cropping systems. Water table depth had no effect on grain yield and N uptake. Previous published results from the same site indicated decreased soil N-NO − 3 content in the top 1 m of the soil profile in the fall of 1993 and less denitrification due to intercropping, demonstrating that a corn–annual rye-grass intercropping system, especially with rye-grass establishing well later in the season, may be an effective practice for increasing soil N uptake without reduction of corn grain yield when adequate N and moisture are present.

Growth and distribution of maize roots under nitrogen fertilization in plinthite soil

To improve efficiency of soil N and water use in the savanna, maize ( Zea mays L.) cultivars with improved root systems are required. Two rainfed field experiments were conducted in Samaru, Nigeria in the 1993 and 1994 growing seasons with five maize cultivars under various rates of nitrogen fertilizer. The capacity of maize for rapid early root growth and to later develop a deep, dense root system was assessed. In addition, the effect of N fertilization on root growth of maize was studied in 1994. The widely cultivated cultivar TZB-SR had a poor root system in the surface soil layer and was more susceptible to early-season drought, as indicated by low plant vigor and aboveground dry matter yield during that time. It had a lower grain yield and a relatively small harvest index, but ranked among the highest in total aboveground dry matter production compared to other cultivars. The size of root system alone did not always relate well with grain yield among cultivars. Partitioning of dry matter within the plant was important in determining differences in grain yield and N stress tolerance between cultivars. A semiprolific cultivar (SPL) had high seedling vigour and a dense root system in the surface soil layer that conferred a greater tolerance to early-season drought stress and improved uptake of the early-season N flush, as indicated by a greater dry matter yield at 35 days after sowing (DAS). It also had a fine, deep, dense root system at flowering that could have improved water- and N-use efficiency in the subsoil (> 45 cm), thereby avoiding midseason drought stress in 1994. SPL had a large harvest index and the greatest yield among cultivars in 1994. Averaged across cultivars, greater root growth and distribution was observed at a moderate N rate of 0.56 g plant −1 than at zero-N or high N (2.26 g plant −1). Differences in root morphology could be valuable as selection criteria for N-efficient and drought-tolerant maize.

Testing CERES–Wheat with Free‐Air Carbon Dioxide Enrichment (FACE) Experiment Data: CO2 and Water Interactions

AbstractDynamic crop‐growth models are used to project the effects of rising atmospheric CO2 concentration and associated climate change on crop yields. Such model predictions are largely untested in the field, for lack of experimental data. We tested the CERES‐Wheat model, modified to include leaf‐level photosynthesis response to elevated CO2, using field data from 2 yr of Free‐Air Carbon Dioxide Enrichment (FACE) experiments with spring wheat (Triticum aestivum L. cv. Yecora Rojo) in Maricopa, AZ. Two irrigation treatments (well‐watered, WW; water‐deficit stressed, WS) and two atmospheric CO2 concentrations (ambient, 350 (μmol mol−1; elevated, 550 (μmol mol−1) were simulated. The model was evaluated using measurements of crop phenology, aboveground dry matter (DM) production, grain yield, and evapotranspiration (ET). Model calculations of crop phenology were within 2 to 3 d of observed values under WW, ambient CO2 conditions in both years. The model did not simulate the accelerated crop phenology (5–8 d at physiological maturity) observed in the WW and elevated CO2 treatments, indicating the need to include effects of increased stomatal resistance on canopy temperature. Simulations of DM and grain yield were within 10% of measured values, except for a tendency to overcalculate DM response to CO2 by 10 to 15% in Year 1 for WS treatments. The model undercalculated cumulative ET under WW conditions by 15%; model sensitivity analyses suggest that simulation of potential evapotranspiration (PET) was too low for this arid site. The model reproduced measured dynamics of CO2‐water interactions. Simulated reductions in water loss due to elevated CO2 were about 4%, in agreement with measurements. The model simulated larger increases in DM production and yield due to elevated CO2 under WS than under WW conditions. In Year 1, simulated crop response to CO2 was 2% larger (measured: 3%) under WS than under WW conditions; in Year 2, it was 11% larger (measured: 9%). The ability to simulate CO2‐water interactions, though it needs to be further evaluated with additional experimental datasets, is an important attribute of models used to project crop yields under elevated CO2 and climate change.

Methane emissions from ricefields as affected by organic amendment, water regime, crop establishment, and rice cultivar

Methane fluxes from Beijing ricefields as affected by organic amendment, water regime, crop establishment method, and rice cultivar were measured with a closed chamber method in 1990, 1991, 1995, and 1996. Total fluxes from plots receiving high organic amendment always exceeded those from the low-input plots. Compared with continuous flooding, intermittent irrigation (there were a few days of no standing water between two irrigations) and constant moisture (the field had no standing water, but remained saturated) reduced methane emission rate by 25.4 and 58.4%, respectively. Methane flux from a dry-seeded rice field was 75.2% lower than from a transplanted ricefield although both dry-seeded rice plots and transplanted ricefields were initially flooded at the same time. Rice cultivars differed in methane emission rates by 9.0–55.7%. Emission rates were positively correlated with aboveground dry matter production and root weight, but not grain yield. Intermittent irrigation and rice cultivar seem to be the most promising methods for mitigating methane emission from ricefields; they do not affect rice yield and are easily implemented at the farm level.