Alfalfa Forage Yield Research Articles

Changes in alfalfa forage quality and stem carbohydrates induced by arbuscular mycorrhizal fungi and elevated atmospheric CO2

Alfalfa is a widely distributed forage legume whose leaves are high in protein content and whose stems are suitable for bioethanol production. However, alfalfa forage digestibility, quality and yield may vary under future climate change scenarios. This legume can establish double symbiosis with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi (AMF). The presence of AMF can modify the evolution of biomass production and partitioning during the vegetative growth of alfalfa. We hypothesised that mycorrhizal symbiosis may change the quantity and/or quality of carbohydrates and lignin in leaves and/or stems of alfalfa, with these changes being dependent on the atmospheric CO2 concentration at which plants are grown. Results showed that mycorrhizal alfalfa plants exposed to elevated CO2 had improved leaf, stem and root biomass, enhanced amount of hemicellulose and decreased concentration of lignin in cell walls of leaves as well as increased levels of glucose and fructose in stems compared with non-mycorrhizal alfalfa. These results indicated improved forage quality (leaves) and enhanced potential for bioethanol conversion (stems) in mycorrhizal alfalfa cultivated under elevated CO2. Moreover, the potential of stems for producing CH4 reinforced their suitability for the conversion of biomass into bioethanol.

Field‐scale potassium and phosphorus fluxes in the bioenergy crop switchgrass: Theoretical energy yields and management implications

AbstractOur understanding of how mineral nutrition affects productivity and composition of bioenergy crops grown on marginal lands remains fragmented and incomplete despite world‐wide interest in using herbaceous biomass as an energy feedstock. Our aim was to determine switchgrass (Panicum virgatum L.) biomass production and maize (Zea mays L.) grain yield on marginal soils used previously to evaluate the effect of soil phosphorus (P) and potassium (K) fertility on alfalfa (Medicago sativa L.) forage production. Grain yield of maize was reduced on P‐ and/or K‐limited plots that also impaired alfalfa forage yield, whereas switchgrass biomass yields were high even in plots possessing very low available P (4 mg kg–1) and K (< 70 mg kg–1) levels. Linear‐plateau regression models effectively described the relationship of soil test P and K to tissue P and K concentrations, and tissue P and K concentrations accurately predicted removal of P and K in harvest biomass. However, neither soil‐test P and K, nor tissue P and K concentrations were effective as diagnostics for predicting switchgrass biomass yield nor could soil tests and their change with cropping predict nutrient removal. Concentrations of cellulose, hemicellulose, lignin, and ash were not influenced by P and K nutrition. Predicted bio‐ethanol production was closely associated with biomass yield whereas high biomass K concentrations reduced estimated bio‐oil production per hectare by as much as 50%. Additional research is needed to identify diagnostics and managements to meet the bioenergy production co‐objectives of having high yield of biomass with very low mineral nutrient concentrations (especially K) while sustaining and improving the fertility of marginal soils.

Impact of atmospheric precipitation on forage yield of alfalfa in droughty conditions of the Volga region

For 22 years (1989–2010), the productivity of alfalfa cultivars Eruslanka and Artemida were studied in terms of irrigation on chestnut soil. During fluctuation of the green mass yield of three cuttings of second year alfalfa from 16.5 and 18.4 to 74.0 and 74.8 t/ha, its nonlinear dependence on precipitation was established. The relation between winter precipitation (November-March) and the yield was not revealed.

Effects of cutting height on shoot regrowth and forage yield of alfalfa (Medicago sativa L.) in a short‐term cultivation system

AbstractAlfalfa (Medicago sativa L.) has been cultivated increasingly widely in the arable area of the middle‐eastern regions of China as a short‐term (1 or 2 years) component of a forage–grain rotation system, but little is known about the harvesting technique for this legume in the short‐term rotation. This study investigated the effects of cutting height (0‐, 5‐ and 10‐cm stubble height above the soil surface) on shoot regrowth and forage yield of alfalfa in the second‐year growing season at two sites in Shandong Province, China. Forage yield at the first harvest was higher under lower cutting height (0 > 5 > 10 cm) at both sites due to greater length and weight of individual shoots harvested. At the site where plants were fertilized and irrigated after the first harvest, lower cutting height increased the number of buds during the early regrowth period and the number of shoots per plant at the second harvest, though it decreased the length and weight of individual shoots harvested. At the site without fertilizer and irrigation, lower cutting height delayed the sprouting of buds after defoliation, and decreased the length of shoots harvested at the second cut. Forage yield at the second harvest was ranked 0 ≈ 5 > 10 cm under fertilizer and irrigation, and 0 ≈ 5 ≈ 10 cm under no fertilizer and irrigation. The path analysis showed that forage yield was affected primarily by the weight of individual shoots at the first cut and by shoot number per plant in the aftermath. Harvesting close to the ground is considered to be a management option to increase alfalfa yield in a short‐term forage production system subjected to irrigation and fertilizer.

Validation of the EPIC model and its utilization to research the sustainable recovery of soil desiccation after alfalfa (Medicago sativa L.) by grain crop rotation system in the semi-humid region of the Loess Plateau

In the semi-humid region of the Loess Plateau in China, dry soil layers in deep soil after alfalfa (Medicago sativa L.) have significantly obstructed the development of sustainable agriculture. However, how to recover soil desiccation sustainably and how to develop a sustainable alfalfa–grain crop rotation system are still unclear. Based on a set of long-term experimental data, the development and recovery of soil desiccation, the forage yield of alfalfa and the grain yield of following crops were researched by the combination of simulation method and investigation method. Some suggestions were proposed for farmers to sustainably recover soil desiccation in deep soil using grain crop rotation system. Validation results showed that (1) EPIC model estimated well both monthly soil water and vertical distribution of soil water in different soil layers for alfalfa–grain crop rotation system and (2) the EPIC model was an effective tool to research the development and recovery of soil desiccation in the Loess Plateau by using validated parameters. Simulation results showed that: (1) It was difficult to restore soil water in deep soil by crop rotation; soil water in the soil below 10m depth should not be lower than 12%, during the cultivation of alfalfa, (2) Alfalfa stand age should not longer than 10 years in the semi-humid region of the Loess Plateau with the mean annual rainfall of 550–600mm, and (3) cultivating shallow root crops such as potato and soybean was better to recover soil desiccation after alfalfa.

Alfalfa forage digestibility, quality and yield under future climate change scenarios vary with Sinorhizobium meliloti strain

Elevated CO2 may decrease alfalfa forage quality and in vitro digestibility through a drop in crude protein and an enhancement of fibre content. The aim of the present study was to analyse the effect of elevated CO2, elevated temperature and Sinorhizobium meliloti strains (102F78, 102F34 and 1032 GMI) on alfalfa yield, forage quality and in vitro dry matter digestibility. This objective is in line with the selection of S. meliloti strains in order to maintain high forage yield and quality under future climate conditions. Plants inoculated with the 102F34 strain showed more DM production than those inoculated with 1032GMI; however, these strains did not show significant differences with 102F78 plants. Neutral or acid detergent fibres were not enhanced in plants inoculated with the 102F34 strain under elevated CO2 or temperature and hence, in vitro dry matter digestibility was unaffected. Crude protein content, an indicator of forage quality, was negatively related to shoot yield. Plants inoculated with 102F78 showed a similar shoot yield to those inoculated with 102F34, but had higher crude protein content at elevated CO2 and temperature. Under these climate change conditions, 102F78 inoculated plants produced higher quality forage. However, the higher digestibility of plants inoculated with the 102F34 strain under any CO2 or temperature conditions makes them more suitable for growing under climate change conditions. In general, elevated CO2 in combination with high temperature (Climate Change scenario) reduced IVDMD and CP content and enhanced fibre content, which means that animal production will be negatively affected.

Fall Harvesting of Alfalfa in North Dakota Impacts Plant Density, Yield, and Nutritive Value

Alfalfa (Medicago sativa L.) is often not harvested in North Dakota during the fall because producers fear the risk of winter-kill and stand reduction. The objective of this study was to determine the impact of a fall harvest on plant density, forage yield, and nutritive value of alfalfa. Two replicated experiments were planted and evaluated in Fargo, ND. Experiment 1 was conducted from 2004 to 2008 and Experiment 2 from 2007 to 2011. Treatments in the two experiments were either a 3-cut system with no fall harvest or a 4-cut system with a fall harvest. Analysis was conducted across experiments and years. In certain years, plant density was significantly reduced when alfalfa was harvested in the fall. The 4-cut system, which included a fall harvest, had significantly greater seasonal forage yield. The total seasonal forage yield for the 4-cut system was approximately 1.04 to 3.88 Mg/ha greater than that of the 3-cut system. However, including a fall harvest decreased forage yield in the first cut the following season. In general, a fall harvest of alfalfa increases seasonal forage yield without reducing stand persistence and overall forage nutritive value.

Evaluation of crop yield and soil water estimates using the EPIC model for the Loess Plateau of China

Since 2000, a database of crop and soil parameters, and meteorological data and so on, has been set up for the EPIC model, based on long-term experimental data and on-the-spot investigated data. The model parameters have been repeatedly revised and verified by data assimilation methods, so the EPIC model can be adopted for the grassland and grain-crop field systems in the Loess Plateau of China. All relevant results showed that the water contents with winter wheat, spring maize, alfalfa and A. adsurgen can be well estimated using the EPIC model (the RMSEs were 20.4 mm, 49.5 mm, 191.92 mm and 136.70 mm, respectively); the simulated winter wheat and spring maize grain yield and the simulated dry forage yield of alfalfa and A. adsurgen were acceptable within the estimation precision (the RMSEs were 0.899 t/hm 2, 0.803 t/hm 2, 1.89 t/hm 2 and 1.06 t/hm 2, respectively).

Alteração no método centroide de avaliação da adaptabilidade genotípica

O objetivo deste trabalho foi alterar o método centroide de avaliação da adaptabilidade e estabilidade fenotípica de genótipos, para deixá-lo com maior sentido biológico e melhorar aspectos quantitativos e qualitativos de sua análise. A alteração se deu pela adição de mais três ideótipos, definidos de acordo com valores médios dos genótipos nos ambientes. Foram utilizados dados provenientes de um experimento sobre produção de matéria seca de 92 genótipos de alfafa (Medicago sativa) realizado em blocos ao acaso, com duas repetições. Os genótipos foram submetidos a 20 cortes, no período de novembro de 2004 a junho de 2006. Cada corte foi considerado um ambiente. A inclusão dos ideótipos de maior sentido biológico (valores médios nos ambientes) resultou em uma dispersão gráfica em forma de uma seta voltada para a direita, na qual os genótipos mais produtivos ficaram próximos à ponta da seta. Com a alteração, apenas cinco genótipos foram classificados nas mesmas classes do método centroide original. A figura em forma de seta proporciona uma comparação direta dos genótipos, por meio da formação de um gradiente de produtividade. A alteração no método mantém a facilidade de interpretação dos resultados para a recomendação dos genótipos presente no método original e não permite duplicidade de interpretação dos resultados.

Forage Yield and Quality of Chicory, Birdsfoot Trefoil, and Alfalfa During the Establishment Year

As part of a study to evaluate alternative forages for farmed deer, we compared forage yields and quality of birdsfoot trefoil (Lotus corniculatus) and forage chicory (Cichorium intybus) with that of alfalfa (Medicago sativa) in north central Alberta, Canada. Despite similar plant densities among the three species, the foliar cover of chicory averaged 76%, 20% greater than alfalfa and 50% greater than trefoil. Alfalfa had higher plant height, dry matter yields, and crude protein concentrations compared to chicory and trefoil, leading to crude protein yields nearly double that of the other forages. Alfalfa also had superior over-winter persistence. Birdsfoot trefoil stands exhibited poor competitiveness in the year of establishment, as demonstrated by high weed and volunteer clover biomass. Chicory had lower neutral detergent fiber concentrations compared to the other forages, leading to a favorable neutral detergent soluble value of 590 g kg-1 DM, 6% greater than that of trefoil. In contrast, tannin concentrations were greatest in trefoil (nearly 60 g kg-1 DM), well above those in the other forages (<20 g kg-1 DM). These results highlight the potential of chicory for forage production, as well as the importance of mixing alfalfa with alternative forages to optimize forage yield and quality.

The Long‐Term Impact of Phosphorus and Potassium Fertilization on Alfalfa Yield and Yield Components

Addition of P and K fertilizer can increase alfalfa (Medicago sativa L.) yield and stand persistence, but the yield components associated with P‐ and K‐induced variation in agronomic performance are not clear. Our objectives were: (i) to determine the impact of P and K nutrition on productivity of a relatively old alfalfa stand; and (ii) determine which yield components are associated with changes in alfalfa forage yield. Treatments were a factorial combination of four P and five K rates replicated four times. Forage harvests occurred four times annually. Plant populations were determined in early December and late May each year. When compared to unfertilized plots, addition of P and K increased forage yield each year. Fertilization with P decreased plants m−2 at all K application rates, but especially in plots fertilized with P, but not K. By comparison, plots fertilized with K, but not fertilized with P, had the higher plant population densities. Although regression analysis eventually revealed a positive association between forage yield and shoots m−2 in 2003 and 2004, the greatest forage yields were not obtained in plots with the greatest plant population densities, shoots plant−1 or shoots m−2 Regression and path analysis revealed that improved forage yield in P‐ and K‐fertilized plots was consistently associated with greater mass shoot−1

Tillage System and Seeding Time Effects on Forage and Seed Yield of Alfalfa and Bromegrass

Perennial forages are an important component for the cropping systems of the Parkland region in the Canadian prairies, but only a few studies have reported on direct seeding of forages in northeastern Saskatchewan. The objective of this study was to compare the effects of tillage (conventional tillage, CT, and zero tillage, ZT) for seedbed preparation and different seeding times (October 1993, May 1994, and June 1994) on forage and seed yield of alfalfa (Medicago sativa Leyss) and bromegrass (Bromus inermis Lyess) on Gray Luvisol (Typic Cryoboralf) soils (sandy at Gronlid and clayey at Ridgedale) in northeastern Saskatchewan. Visual inspection of plant stands in the establishment year indicated that plant densities were generally higher under CT than ZT and with spring than autumn seeding. Forage yield in 1994 was greater under ZT than CT for alfalfa at both sites and for bromegrass at Ridgedale. In 1995 and 1996, tillage had no effect on forage yield in most cases. The 3‐year forage production was greater under ZT than CT for alfalfa by 647 and 770 kg ha−1 at Gronlid and Ridgedale, respectively, and for bromegrass at Ridgedale (by 697 kg ha−1), with the opposite result at Gronlid (by 237 kg ha−1). The effect of seeding time on forage production was not consistent. The seed yield in 1995 and 1996 was somewhat greater with ZT than CT, with autumn than spring seeding, and with May than June seeding for alfalfa, whereas the opposite was true for bromegrass, except at Ridgedale when autumn seeding produced greater seed yield than spring seeding. In summary, the lower plant population under ZT than CT in the establishment year did not necessarily result in lower forage and seed yield of alfalfa and bromegrass, suggesting that ZT can replace CT for forage production, and seeding time effect was mainly observed in the first year.

Availability and contributions of soil phosphorus to forage production of seeded alfalfa in semiarid Loess Plateau

The availability of soil phosphorus was studied in response to the forage production of seeded alfalfa ( Medicago sativa L.), established by the ridge and furrow water-harvesting technique in the semiarid Loess Plateau of China. The following 5 treatments were set up in this study: (1) conventional cultivation in a flat plot without mulch (CK); (2) plastic mulched ridge with 30 cm width of ridge and furrow (M30); (3) plastic mulched ridge with 60 cm width of ridge and furrow (M60); (4) bare ridge with 30 cm width of ridge and furrow (B30); (5) bare ridge with 60 cm width of ridge and furrow (B60). The forage yield, evapotranspiration (ET), soil organic carbon (SOC), total phosphorus, available phosphorus and the ratio of soil organic C to available P (C/P) were measured in the experiment. Results showed that the positive correlation occurred between the decrease in soil available P and the total forage yield of alfalfa after three-year alfalfa stand. M30 and M60 were higher than those of conventional flat cultivation (CK) by 10.7% and 40.3%, respectively, whereas the yield of two bare treatments (B30 and B60) was lower than that of CK by 14.2% and 28.3%, respectively. After a 3-year alfalfa stand, the trend of the decrease in soil available P was in the order of M60 (55.5%) > M30 (51.5%) > CK (34.6%) > B30 (23.4%) > B60 (17.5%). Moreover, after 3-year alfalfa growth, the C/P ratio increased significantly in all of the treatments by comparing with that before sowing. The C/P ratios of M30 (1165.1) and M60 (1326.1) were significantly higher than those of the other treatments. More interesting finding was that the increase in SOC in dry years promoted the accumulation of soil available P. However, in wet years, the increase of SOC limited the accumulation of soil available P. Therefore, to further increase the forage yield of alfalfa, the effective technique must be developed to increase the soil available P.

EFFECT OF RIDGE AND FURROW MICRO-CATCHMENT ON SOIL WATER IN SEEDED MEDICAGO SATIVA GRASSLAND IN THE SEMIARID LOESS HILL AND GULLY REGION OF NORTHWESTERN CHINA

Aims The semiarid loess hill and gully region of northwestern China is a pasture and agriculture transitional zone lacking water resources for irrigation. The agroecosystem in this region is very vulnerable. An effective method to improve the ecosystem is to combine agriculture with animal husbandry, in which productive grassland plays a key role. However, water is the main limitation on grassland production in this region. We studied the effect of alternating ridges and furrows (for harvesting rainfall) on alfalfa (Medicago sativa) forage yield and soil water. Methods Five treatments were compared: 1) conventional cultivation in a flat plot without mulch (CK), 2) plastic mulched ridges with 30 cm wide ridges and furrows (M30), 3) plastic mulched ridges with 60 cm wide ridges and furrows (M60), 4) bare ridges with 30 cm wide ridges and furrows (B30), and 5) bare ridges with 60 cm wide ridges and furrows (B60). We measured soil water consumption, forage yield of alfalfa and soil water profile in all treatments. Important findings The water use efficiency of M30 and M60 treatments was greater than that of CK by 13% and 41%, respectively. The total forage yield of alfalfa of M30 in four years was not significantly different from that of CK, but the total forage yield of M60 was significantly higher than that of CK by 41%. In both bare treatments, the total forage yield of alfalfa was lower than in CK. In the 3rd alfalfa growing season, the 150 cm soil layer was the balance point of water supplement and soil water consumption. Below 150 cm, soil water can not be supplied by rainfall. Water at 200-500 cm soil depth was close to the permanent wilting point after four years. This study indicates that the M60 treatment is the optimum model for alfalfa establishment in this region. However, after the alfalfa phase, the shallow-root crop must be planted to restore soil water content for subsequent conventional crops.

Dynamics of soil organic carbon and soil fertility affected by alfalfa productivity in a semiarid agro-ecosystem

We explore the dynamics of soil organic carbon of various forms and its relation with soil fertility in seeded alfalfa grassland established using a field micro-catchment technique to harvest water on the semiarid Loess Plateau in China. Five regimes were set up: (1) conventional flat cultivation without mulch (CK), (2) ridges and furrows were set up alternately on flat land, with 15 cm between each so that the distance between successive ridges (or successive furrows) was 30 cm, and the ridges were mulched with plastic film (M30), (3) similar to M30, but with twice the distance between furrows and ridges (M60), (4) similar to M30, but the ridges were not mulched (B30), (5) similar to M60, but the ridges were not mulched (B60). The increase in alfalfa forage yield in the mulch regimes promotes soil organic carbon (SOC) content, the light fraction of organic carbon (LFOC), the heavy fraction of organic carbon (HFOC) and microbial biomass carbon (MBC). MBC was significantly higher in M30 and M60 than in the other regimes. Significant positive correlation is found between MBC and LFOC (R=0.89; P<0.0001), and MBC and HFOC (R=0.82; P=0.00016). At the end of our three-year experiment, the C/N ratio of 10.09 in M60 was significantly (P<0.005) higher than the other regimes. Since a lower C/N ratio accelerates SOC decomposition in this region, the higher C/N ratio in M60 could limit mineralization of soil nitrogen, conserving soil nitrogen and SOC. The lower ratio of nitrate and nitrite nitrogen to total nitrogen, of 10.74, in M60 at the end of this experiment than in the other regimes and before sowing supports this point. The correlations of SOC with available P and with the ratio of available P to total P are positive in the dry year of 2001, but negative in the wet year of 2002. This can be explained on the basis that a high forage yield of alfalfa requires more soil available P in the wet years than in the dry years.

Soil water and alfalfa yields as affected by alternating ridges and furrows in rainfall harvest in a semiarid environment

We studied the effect of alternation of ridge and furrow for harvesting rainfall on alfalfa ( Medicago sativa L.) grassland performance in the 3 years of 2001–2003. Five treatments were designed in this study: (1) conventional cultivation in a flat plot without mulch (CK), (2) plastic-mulched ridge with both ridge and furrow 30 cm wide (M30), (3) plastic-mulched ridge with both ridge and furrow 60 cm wide (M60), (4) bare ridge with both ridge and furrow 30 cm wide (B30) and (5) bare ridge with both ridge and furrow 60 cm wide (B60). Treatments of mulching ridge/furrow improved water and temperature conditions in the topsoil (0–20 cm) in mid-April. Mulching ridge/furrow increased growth of the individual alfalfa plants, and decreased the plant density. Mulching ridge/furrow helped alfalfa absorb water from the deep soil. The total forage yield of alfalfa in M30 and M60 treatments in the 3 years was higher than in control (CK) by 10.7 and 40.3%, respectively. On the basis of the 0–500 cm soil layer, the water use efficiency (WUE) was 8.12 and 9.97 kg ha −1 mm −1 in M30 and M60, respectively, whereas it was only 7.20 kg ha −1 mm −1in CK. The total forage yield of alfalfa in B30 and B60 in the 3 years was lower than that in CK by 14.2 and 28.3%, respectively. The WUE was only 6.26 and 5.38 kg ha −1 mm −1 in B30 and B60, respectively, significantly lower than that in CK. It is concluded that mulching the 60 cm wide ridges with 60 cm wide furrows serve as a model for alfalfa establishment on large scale in the semiarid region.

Comparative forage yield, water use, and water use efficiency of alfalfa, crested wheatgrass and spring wheat in a semiarid climate in southern Saskatchewan

Crested wheatgrass (Agropyron cristatum L. Gaertn.) and alfalfa (Medicago sativa L.) are introduced forage species used for hay and grazing by cattle across western Canada. These species are well adapted to the semiarid region but their long-term responses to water stress have not been previously compared. Two alfalfa cultivars with contrasting root morphology (tap-rooted vs. creeping-rooted) and two crested wheatgrass (CWG) cultivars with different ploidy level (diploid vs. tetraploid) were compared with continuously cropped spring wheat (Triticum aestivum L.) for 6 yr at a semiarid location in western Canada. Soil water depletion, forage yield, water use efficiency, leaf water potential, osmotic potential and turgor were compared. There were no consistent differences between cultivars within alfalfa or CWG for variables measured. However, these two species exhibit different water stress response strategies. Leaf water potential of CWG was lower during midday stress period than that of alfalfa or wheat. Alfalfa apparently had greater capacity to osmotically adjust to avoid midday water stress and maintain higher turgor. Soil water use patterns changed as the stands aged. In the initial years of the trial, forage crops used soil water from upper layers of the profile. In later years, soil water was depleted down to 3 m by alfalfa and to 2 m by crested wheatgrass. Alfalfa was able to deplete soil water to lower concentrations than crested wheatgrass or wheat. Soil water depletion by wheat during the non-active growth season (after harvest to fall freeze-up) was much less than for CWG or alfalfa as expected for annual vs. perennial crops. As a result, more soil water was available to wheat during its active growth period. In the last 3 yr, the three species depleted all available soil water. Forage yield responses also changed over time. In the initial 3 yr, crested wheatgrass yielded as much as or more than alfalfa. For the last 3 yr of the experiment, alfalfa yielded more forage than crested wheatgrass. Forage crops deplete much more soil water during periods of aboveground growth dormancy than wheat. Water use efficiency of crested wheatgrass declined with stand age compared with fertilized continuous spring wheat. Alfalfa exhibited deep soil water extraction and apparent osmotic adjustment in response to water stress while CWG exhibited tolerance of low water potential during stress. Key words: forage yield, soil water, water potential, water use, water use efficiency, drought

Soil quality responses to alfalfa watered with a field micro-catchment technique in the Loess Plateau of China

This paper explores the soil responses to alfalfa that is established using a field micro-catchment technique to harvest water under semiarid conditions. The field micro-catchment technique involved setting up ridges and furrows alternately on the flat land. The ridges served as the rainfall harvesting zone and the furrows as the planting zone. Five treatments were set up in this study: (1) conventional cultivation in a flat plot without mulch (CK), (2) plastic mulched ridge with 30 cm width of ridge and furrow (M30), (3) plastic mulched ridge with 60 cm width of ridge and furrow (M60), (4) bare ridge with 30 cm width of ridge and furrow (B30), (5) bare ridge with 60 cm width of ridge and furrow (B60). The mulching treatments increased the productivity of seeded alfalfa and significantly ( p < 0.05) increased water use efficiency, causing the soil organic carbon (SOC), total soil nitrogen (TSN) and C/N ratio to increase. We also found that the alfalfa root system was very good at breaking up the plowing pan created by many years of tillage. In the M30 and M60 treatments, the total forage yield during the 3 years was higher than in CK by 10.7% and 40.3% respectively, whereas the total forage yield over the 3 years in the B30 and B60 treatments were lower than in the CK treatment by 14.2% and 28.3%, respectively. The water use efficiency in the mulching treatment was significantly higher than in the other treatments. After 3 years (2001–2003), the SOC content in ridge and furrow treatments (M30, M60, B30 and B60) was increased by 7.4%, 14.2%, 4.5% and 1.8%, respectively, contrasting with a decrease of 3.5% in the CK treatment. The increase in SOC positively correlated ( R 2 = 0.6257) with the forage yield of alfalfa in the ridge and furrow treatments. The TSN for CK, M30, M60, B30 and B60 increased by 0.35%, 1.70%, 2.30%, 0.75% and 0.64%, respectively by the end of the 3 years. However, we found that the available phosphorus (P) in the mulch treatments during the 3-year period decreased rapidly indicating that it is necessary to apply P fertilizer to alfalfa-cultivated land under these management conditions. In conclusion, the ridge and furrow with mulch treatments, especially M60 treatments, proved to be a better pattern for alfalfa establishment, soil quality and nutrient cycling under semiarid conditions.

Influence of Phosphorus and Potassium on Alfalfa Yield and Yield Components

Phosphorus and K fertilization increases alfalfa (Medicago sativa L.) yield and stand persistence, but the changes in yield components as affected by P and K fertility level are not known. Our hypothesis is that P and (or) K fertilization will increase one or more alfalfa yield components, and those component responses may change with stand age. The objectives of this field study were to determine the impact of P and K fertilization on alfalfa forage yield and yield components during the initial 3 yr after establishment. Treatments were the factorial combinations of four P rates (0, 25, 50, and 75 kg P ha−1) and five K rates (0, 100, 200, 300, and 400 kg K ha−1) arranged in a randomized complete block design with four replications. Forage harvests occurred four times annually, and yield, mass shoot−1, and shoots area−1 were determined. Plant populations were determined in early December and late May each year. Incremental additions of P and K increased alfalfa yield in each year. Potassium fertilization did not influence plant population, while robust P-responsive alfalfa plants apparently crowded out smaller, less vigorous plants thus decreasing plants m−2 Stand assessments based on shoot counts, or aboveground plant counts may not accurately indicate alfalfa yield potential. Shoots plant−1 was not affected by application of either nutrient, while shoots m−2 generally declined with increased P and K fertilization. Improved forage yield of P- and K-fertilized plots was consistently associated with greater mass shoot−1 Because fertilizer-responsiveness is closely associated with greater mass shoot−1, cultivars possessing this trait may be relatively more productive under well-fertilized conditions.

Influence of Late Season Harvesting, Fall Grazing, and Fungicide Treatment on Verticillium Wilt Incidence, Plant Density, and Forage Yield of Alfalfa.

Studies were conducted in the presence of Verticillium wilt (Verticillium albo-atrum) to determine the effect of fall harvesting and grazing over time on plant stand and forage yield of alfalfa (Medicago sativa). Resistant and susceptible cultivars were tested on established and newly seeded fields. In the fall (experiments 1 and 2), cultivars were either: (i) cut (third time); (ii) grazed; (iii) cut and grazed; or (iv) left uncut and ungrazed. Although Verticillium was present, test sites for experiments 2 and 3 were sprayed with a spore suspension of V. albo-atrum immediately following the first cutting of each experiment to standardize disease pressure. In experiment 1, the moderately resistant cultivar Apollo II, harvested twice without a late third cutting or fall grazing, produced the highest forage yield the following year. Fall grazing reduced subsequent yields in both the 2- and 3-cut treatments. In experiment 2, a third cutting decreased plant density and forage yield in both resistant and susceptible cultivars, while grazing had no effect. Neither fall treatment affected incidence of Verticillium wilt. In experiment 3, application of the fungicide benomyl to plant stubble following each harvest decreased Verticillium wilt in Apollo but not in Arrow. Overall, with the resistant cultivar Arrow, harvesting twice annually and grazing after a killing frost in lieu of late fall cutting slowed disease development, prolonged stand life, and maximized forage yield and quality.