Can mineral and organic fertilization help sequestrate carbon dioxide in cropland?

The soil organic matter content represents a huge reservoir of plant nutrients and an effective safeguard against pollution; beside it can sequestrate atmospheric CO₂. Since 1966 up to now in the Southeast Po valley (Italy), the soil organic C (SOC) and total N (TN) dynamics in the 0–0.40 m soil layer under a maize–wheat rainfed rotation are studied as influenced by organic and mineral N fertilizations. Every year in the same plots cattle manure, cattle slurry, and crop residues (i.e. wheat straw and maize stalk) are ploughed under to 0.40 m depth at a same dry matter rate (6.0 and 7.5 t DM ha⁻¹ year⁻¹ after wheat and maize, respectively) and are compared to an unamended control. Each plot is splitted to receive four rates of mineral fertilizer (0–100–200–300 kg N ha⁻¹). In the whole experiment, in 2000 SOC concentration was lower than in 1966 (6.77 and 7.72 g kg⁻¹, respectively), likely for the deeper tillage that diluted SOC and favoured mineralization in deeper soil layer. From 1972 to 2000 SOC stock did not change in the control and N fertilized plots, while it increased at mean rates of 0.16, 0.18, and 0.26 t ha⁻¹ year⁻¹ with the incorporation of residues, slurry and manure, corresponding to sequestration efficiencies of 3.7, 3.8 and 8.1% of added C with the various materials. TN followed the same SOC dynamic, demonstrating how it depends on the soil organic matter. Manure thus confirmed its efficacy in increasing both SOC content and soil fertility on the long-term. In developed countries, however, this material has become scarcely available; slurry management is expensive and implies high environmental risks. Moreover, in a C balance at a farm (or regional) scale, the CO₂ lost during manure and slurry stocking should be considered. For these reasons, the incorporation of cereal residues, even if only a little of their C content was found capable of soil accumulation, appears the best way to obtain a significant CO₂ sequestration in developed countries. Our long-term experiment clearly shows how difficult it is to modify SOC content. Moreover, because climate and soil type can greatly influence SOC dynamic, to increase CO₂ sequestration in cropland, it is important to optimize the fertilization within an agricultural management that includes all the agronomic practices (e.g. tillage, water management, cover crops, etc.) favouring the organic matter build up in the soil.     

White lupine as a beneficial crop in Southern Europe. II. Nitrogen recovery in a legume–oat rotation and a continuous oat–oat

One experiment lasting for two years was carried out at Pegões (central Portugal) to estimate the impact of mature white lupine residue (Lupinus albus L.) on yield of fodder oat (Avena sativa L. cv. Sta. Eulalia) as the next crop in rotation, comparing with the continuous cultivation of cereal, under two tillage practices (conventional tillage and no-till) and fertilized with five mineral nitrogen (N) rates, with three replicates. Oat as a first crop in the rotation provided more N to the agro-ecosystem (63 kg N ha⁻¹) than did lupine (30–59 kg N ha⁻¹). This was at a cost of 100 kg of mineral N ha⁻¹, whereas lupine was grown without addition of N. A positive response of oat as a second crop was obtained per kg of lupine-N added to the system when compared with the continuous oat–oat. The cereal also responded positively to mineral N in the legume amended soil in contrast with the oat–oat sequence where no response was observed, partly due to the fast mineralization rate of lupine residue and a greater soil N immobilization in the continuous oat system. Each kg N ha⁻¹ added to the soil through the application of 73 kg DM ha⁻¹ mature lupine residue (above- and belowground material) increased by 72 kg DM ha⁻¹ the oat biomass produced as the second crop in rotation when 150 kg mineral N ha⁻¹ were split in the season, independent of tillage practice. Mature legume residue conserved in the no-tilled soil depressed the yield of succeeding cereal but less than the continuous oat–oat for both tillage practices, where the application of mineral N did not improve the crop response.     

Productive behaviour of “cherry”-type tomato irrigated with saline water in relation to nitrogen fertilisation

Research on tomato tolerance to salt stress indicates that thresholds of ECe for the decrease of yield and plant growth are moderately high and differ among varieties. Some results suggest that nitrogen fertilisation may help increase the threshold for yield reduction. Most literature data have been collected either in small-scale containers or in the open field and both systems are often subjected to disturbances making hypotheses difficult to test. A set of experiments was conducted in large containers in a rainout-shelter field setting to assess the response of a “cherry”-type tomato variety to irrigation with saline water and to test the hypothesis that salt stress may be mitigated through nitrogen fertilisation.Tomato hybrid ‘TOMITO F 1’ was irrigated with water at four levels of salinity (0.7, 2.5, 5.0, and 10.0 dS m⁻¹ ECw) and three levels of nitrogen fertilisation (no added nitrogen = N0, 120 kg ha⁻¹ = N120, and 160 kg ha⁻¹ = N160) in factorial combination. Plant growth and water use were measured throughout the growth cycle, and gas exchange and leaf water potentials were measured at the fruit-growing stage. Two growing cycles were completed, one with high initial soil nitrogen (HN) and the second with low initial soil nitrogen (LN).No interaction was found between the application of nitrogen and plant response to saline irrigation. Plant growth and yield were affected by the saline treatments and less by nitrogen fertilisation, especially in the HN treatment.Irrigations with saline water resulted in increased values of soil salinity. Water use was lower with increasing soil and water EC, and the marginal reduction ranged from about 31 mm for each dS m⁻¹ of water EC at low salinity to about 6 mm for each dS m⁻¹ at high water EC.The marginal reduction in yield ranged from about 3.3 t ha⁻¹ for each dS m⁻¹ at low salinity water to less than 0.6 t ha⁻¹ for each dS m⁻¹ at high EC of irrigation water. Yield reductions were mainly due to lower fruit weight. Biomass values decreased as the salinity levels increased and fruit quality was improved in both cycles with increasing salinity.The hypothesis that nitrogen fertilisation could help tomato plants increase tolerance to salinity was not confirmed by data of this experiment and alterations induced by salinity in plant growth, yield and quality stabilised at high levels of water EC.     

水氮耦合对固定道垄作栽培春小麦根长密度和产量的影响

固定道垄作(PRB)是在农田中设固定的机械行走道的一种垄作和沟灌栽培模式,是河西灌区春小麦取代传统平作和大水漫灌种植方式的一种新技术。为了明确PRB种植模式下合理的施氮水平和灌水量,2014—2015年连续2年采用二因素裂区设计,以3种灌溉定额(1200、2400和3600 m3 hm–2)为主区,以4种施氮水平(0、90、180和270kg hm–2)为副区,研究水氮耦合对小麦不同生育期的根长密度及最终产量的影响。随灌水量和施氮量的增加,根长密度呈现先增后降的变化趋势,且灌水量的效应大于施氮水平的效应;开花、灌浆和成熟期的根长密度与籽粒产量呈正相关。回归分析显示,根长密度最大值的水氮耦合条件是灌水量约2850 m3 hm–2、施氮量196~207 kg hm–2。中等灌水量(2400 m3 hm–2)条件下,小麦主要生育期根长密度显著增加,提高了根长密度在40~80 cm土层的分配比例,增加了水分利用效率和氮肥农学利用效率。综合评价小麦籽粒产量、水分利用率和氮肥农学利用效率,中等灌水量与中氮水平(180 kg hm–2)是所有处理中的最佳水氮耦合模式,可用于河西灌区春小麦PRB栽培模式。当加大灌水至3600m3 hm–2时,产量没有显著增加,水分利用效率和氮肥农学利用效率显著下降,其原因可能是高灌水量使小麦主要生育期的根长密度降低,且根长密度在0~40 cm土层的比例升高,在40~80 cm土层的比例下降。     

Effect of Gluconacetobacter diazotrophicus and Trichoderma viride on soil health, yield and N-economy of sugarcane cultivation under subtropical climatic conditions of India

Intensive cropping and exhaustive nature of sugarcane–wheat–rice cropping system in the Indo-Gangetic Plains of South Asia have led to the depletion of soil organic carbon content and inherent soil fertility resulting in a serious threat to the sustainability of these production systems. Bioagents like Gluconacetobacter diazotrophicus and Trichoderma viride have great potential to restore soil fertility and promote sugarcane growth. Field experiments, therefore, have been conducted to study the integrated effect of bioagents (G. diazotrophicus and T. viride), Farm Yard Manure (FYM) and fertilizer N on sugarcane rhizosphere, crop yield and N economy for two crop cycles during 2004–2006 and 2005–2007 crop seasons at Lucknow, in the middle Indo-Gangetic plain region. Both bioagents could survive and colonize sugarcane rhizosphere and FYM improved their colonization. Enhanced soil microbial population and microbial carbon (SMC) and nitrogen (SMN) with increasing N level were probably due to more available N in the soil. FYM/bioagents amendment further enhanced the microbial carbon. The uniform increase in the fraction of SMC and SMN of total organic carbon indicated that immobilization/mineralization was being maintained in the soil where enhanced microbial biomass might act later as a source of nutrients.Bioagents ammended FYM enhanced the uptake of N, P and K in sugarcane at all the levels of fertilizer N. It was mainly due to the enhanced nutrient availability in the rhizospheric soil as the soil organic C and available N, P and K content increased with the application of bioagents/FYM. A saving of 76.3 kg N ha⁻¹ was envisaged by the use of G. diazotrophicus inoculated FYM with marginal (2.4 t ha⁻¹) decline in the cane yield. Application of T. viride enriched FYM, however, brought economy in the use of fertilizer N by 45.2 kg ha⁻¹ and also increased the yield by 6.1 t ha⁻¹compared to the control treatment. Overall, strategic planning in terms of an integrated application of these bioagents/manures with fertilizer N will not only sustain soil fertility but will also benefit farmers in terms of reducing their dependence and expenditure on chemical fertilizers.     

White lupine as a beneficial crop in Southern Europe: I. Potential for N mineralization in lupine amended soil and yield and N2 fixation by white lupine

Two experiments were carried out at Pegões (central Portugal) to determine the potential N mineralization in a pulse amended disturbed and undisturbed soil incubated at several temperatures, and to evaluate for 2 years the yield and N₂ fixation capacity of sweet lupine (Lupinus albus L. cv. Estoril) inoculated with a mixture of rhizobia strains or nodulated by indigenous soil bacteria and submitted to conventional tillage or no-till practices. A completely randomized block design for soil mobilization with three replicates was used for the laboratory study, and completely randomized blocks for inoculation and tillage treatments with four replicates were used for the lupine yield and N₂ fixation experiment. Residue N immobilization occurred immediately after mature residue return to the soil independent of temperature, and was greater at 7 °C especially in the disturbed topsoil. Greater immobilization was also observed by doubling the amount of mature residue incorporated in the soil. This was expected since soil microorganisms would be in direct contact with the fresh organic matter and would be provided with more organic carbon under these circumstances. Nitrogen mineralization proceeded after 5 days of amendment. Potential N mineralization was higher at 25 °C than at 18 or 7 °C, for both conventional and no-till practices. At 25 °C, 42% of buried residue-¹⁵N was released over 210 days, at a smaller rate than 18 °C (49%) over 81 days. Lupine yield and N₂ fixation capacity were similar in plots that were not inoculated and those receiving the mixture of three rhizobia strains. White lupine had an efficient symbiosis with indigenous soil rhizobia at pod-filling (>99%, >100 kg N ha⁻¹ year⁻¹) which was not affected by tillage. At this stage, plant residue including visible roots and nodules accounted for a soil N input of +96 kg ha⁻¹ year⁻¹ (91% of crop N), showing the large soil N benefit by the crop at this stage. The lupine residue at pod-filling stage can be used as a green manure under the conditions of organic farming systems. The apparent N “harvest” index of the pulse at pod-filling was only 9% though at maturity phase it should result in a higher value and the legume will show a lower fertilizer N value.     

Nitrogen balance and losses through drainage waters in an agricultural watershed of the Po Valley (Italy)

Sustainable agriculture requires assessments of nitrogen fluxes and monitoring of potential nitrate losses. Watershed studies are particularly valuable to calculate nitrogen balances and quantify the relative importance of different sources of inputs and outputs. A nitrogen balance was calculated from September 2004 to October 2006 in an agricultural watershed named Valle Volta (Northern Italy) located in a Nitrate Vulnerable Zone. The area, consisting of 17.4 km² of arable land, with limited presence of urban areas and roads, is entirely below the sea level (3 m b.s.l. in average). Soils are typically Vertic Cambisols and Thionic Fulvisols with fine texture (silty clay or silty clay loam). About 45% of the agricultural soil is pipe-drained. The ground water level is maintained at 4.6 m b.s.l. by the activity of pumps that raise excess waters into a river. Water fluxes in and out from the basin were daily registered, and dissolved inorganic nitrogen concentration (N–NO₃ + N–NH₄) analyzed periodically. Data about fertilizers applications, seeds and crop yield were obtained from farmers’ interviews. Biological nitrogen fixation (BNF) was estimated on the base of dry matter yield. Major N inputs derived from fertilizers (174–188 Mg watershed⁻¹ year⁻¹), followed by BNF (126–131 Mg watershed⁻¹ year⁻¹). Maize was the crop receiving the highest fertilization rates, accounting for more than 40% of total fertilizer inputs. Saleable products were the main form of N leaving the watershed (317–338 Mg watershed⁻¹ year⁻¹). Nitrate was the main N form in irrigation and efflux water; its concentration was higher from autumn to spring, with peaks of 10–20 mg N L⁻¹ in efflux water, while it was low in summer. Nitrogen losses with efflux water were higher in spring and in autumn. Overall, losses of nitrate by efflux water were limited if compared with literature data. Water balance in the area remained near zero at the beginning and the end of the first year, confirming the suitability of the area for this kind of study. The potential net contribution of each hectare of agricultural soil of Valle Volta basin to the N load toward the Adriatic sea is about 5.5 kg N. Our study demonstrated that in the Valle Volta watershed, total N outputs and inputs are of similar magnitude, indicating that crop management and especially N fertilization techniques has reached good levels of ecological sustainability.     

Evaluation of the soil crop model STICS over 8 years against the “on farm” database of Bruyères catchment

The European Water Framework Directive (2000) offers a new challenge for farmers and water policy makers. It requires the establishment of quantitative environmental diagnosis of water quality. This can be done using crop models properly tested in the short and long-terms and taking into account current farming practices. The aim of this paper is to check the robustness of a crop model (STICS) for predicting the nitrogen uptake and nitrate leaching in various fields during 8 successive years. The model was evaluated on the soil–crop database of a small catchment in northern France. It includes data of crop production and N uptake, water and mineral nitrogen contents in soil measured three times a year at 36 sampling sites representative of crops (wheat, sugar beet, pea, barley, oilseed rape) and soil parent materials (loam, loamy clay and rocks, sandy loam and limestone, sand). A few crop parameters of STICS were recalibrated on independent databases in order to improve the predictions obtained with the standard parameterization. STICS was then evaluated either by resetting simulations each year (RS) or during continuous simulations (CS) over the 8 years. A reasonable agreement was obtained between observed and simulated values, except for soil N mineral content at harvest and N content in crop residues. The model efficiencies using CS mode were 0.53, 0.94 and 0.38 for N uptake, soil water and mineral N in late autumn, respectively. The mean calculated drainage was 192 mm y⁻¹ and N leaching was estimated at 20 kg N ha⁻¹ y⁻¹, respectively. Averaging the outputs according to soil and crop type improved the quality of fit. The outputs of CS simulations were close to those obtained with RS. The mean nitrate concentration in water drainage was estimated as 46 and 45 mg NO₃ l⁻¹ with RS and CS, respectively. Continuous simulations did not induce a substantial drift in mineral N in late autumn and can be trusted for predicting nitrate leaching. However, the leaching predictions were more sensitive to spatially variable parameters such as maximal rooting depth and potential mineralisation rate for CS than for RS. This emphasizes the difficulty in extrapolating the model over the long-term for large spatial areas. Another important uncertainty concerns fertiliser use efficiency, which had a small effect on leaching but a marked influence on gaseous N losses. Further assessments of the model will concern the whole N balance prediction over the long-term.     

灌溉水盐度和施氮量对棉花根系分布影响研 究简

 通过田间小区试验,研究了不同灌溉水盐度和施氮量对滴灌棉花根系分布的影响。试验设置3种灌溉水盐度;0.35、4.61和8.04 dS·m^-1（分别代表淡水、微咸水和咸水三种灌溉水类型）;施氮量为0、240、360和480 kg·hm^-2。结果表明,按质量计,棉花的根主要分布在0~20 cm,此部分占根总质量的85%~90%。微咸水和咸水灌溉棉花根的总质量显著降低,分别较淡水灌溉减少10%和36%,尤其在土壤表层0~20 cm和下层60~100 cm显著降低;施用氮肥可以显著增加棉花根的质量。以长度计,棉花根集中分布在0~60 cm,此部分占总根长的87%~96%;60 cm以下根长密度明显降低。微咸水灌溉棉花根长密度最大,其次是咸水,淡水灌溉最低;淡水灌溉下,根长密度随施氮量增加显著降低;微咸水和咸水灌溉下,根长密度随施氮量增加呈先增后降趋势,其中施氮240 kg·hm^-2最高。棉花根表面积表现为微咸水>淡水>咸水,平均根直径为微咸水>咸水>淡水,而不同灌溉水处理间根体积的差异不显著。随着施氮量的增加,根表面积、根体积和平均直径均显著降低。     

Optimized single irrigation can achieve high corn yield and water use efficiency in the Corn Belt of Northeast China

Decreasing the corn (Zea mays L.) gap between the potential yield and farm yield and reducing the risk of grain yield of drought are very important for corn production in the Corn Belt of Northeast China (CBNC). To achieve a high and stable corn yield, the effects of supplementary irrigation on yield, water use efficiency (WUE) and irrigation water use efficiency (IWUE) were studied using a modelling approach. The Root Zone Water Quality Model 2 was parameterized and evaluated using two years of experimental data in aeolian sandy soil and black soil. The evaluated model was then used to investigate responses to various irrigation strategies (rainfed, full irrigation and 12 single irrigation scenarios) using long-term weather data from 1980 to 2012. Full irrigation guarantees a high and stable corn grain yield (12.92 Mg ha⁻¹ and has a coefficient of variation (CV) of 14.8% in aeolian sandy soil; 12.30 kg Ma⁻¹ and CV of 11.1% in black soil), but has a low water use efficiency (19.92 and 21.81 kg ha⁻¹ mm⁻¹) and a low irrigation water use efficiency (10.01 and 11.03 kg ha⁻¹ mm⁻¹). A single irrigation can increase corn yields by 3–35% for aeolian sandy soil and 5–35% for black soil over different irrigation dates compared with no irrigation. The most suitable single irrigation date was during late June to early July for aeolian sandy soil (yield = 10.73 Mg ha⁻¹ and WUE = 27.94 kg ha⁻¹ mm⁻¹) and early to mid-July for black soil (yield = 11.20 Mg ha⁻¹ and WUE = 27.70 kg ha⁻¹ mm⁻¹). The lowest yield risk of falling short of the yield goal of 8, 9, and 10 Mg ha⁻¹ were 9.1%, 18.2%, and 33.33% in aeolian sandy soil and 3.0%, 15.25, and 21.2% in black soil when an optimized single irrigation was applied in late June or early July, respectively. Therefore, an optimized single irrigation should be applied in late June to early July with the irrigation amount to refill soil water storage of root zone to field capacity in CBNC.     

Spatial distribution of soil water,soil temperature,and plant roots in a drip-irrigated intercropping field with plastic mulch

Intercropping and drip irrigation with plastic mulch are two agricultural practices used worldwide. Coupling of these two practices may further increase crop yields and land and water use efficiencies when an optimal spatial distribution of soil water contents (SWC), soil temperatures, and plant roots is achieved. However, this coupling causes the distribution of SWCs, soil temperatures, and plant roots to be more complex than when only one of these agricultural practices are used. The objective of this study thus was to investigate the effects of different irrigation treatments on spatial distributions of SWCs, soil temperatures, and root growth in a drip-irrigated intercropping field with plastic mulch. Three field experiments with different irrigation treatments (high T1, moderate T2, and low T3) were conducted to evaluate the spatial distribution of SWCs, soil temperatures, and plant roots with respect to dripper lines and plant locations. There were significant differences (p < 0.05) in SWCs in the 0–40 cm soil layer for different irrigation treatments and between different locations. The maximum SWC was measured under the plant/mulch for the T1 treatment, while the minimum SWC was measured under the bare soil surface for the T3 treatment. This was mainly due to the location of drippers and mulch. However, no differences in SWCs were measured in the 60 100 cm soil layer. Significant differences in soil temperatures were measured in the 0 5 cm soil layer between different irrigation treatments and different locations. The soil temperature in the subsoil (15 25 cm) under mulch was higher than under the bare surface. The overlaps of two plant root systems in an intercropping field gradually increased and then decreased during the growing season. The roots in the 0 30 cm soil layer accounted for about 60% 70% of all roots. Higher irrigation rates produced higher root length and weight densities in the 0 30 cm soil layer and lower densities in the 30 100 cm soil layers. Spatial distributions of SWCs, soil temperatures, and plant roots in the intercropping field under drip irrigation were significantly influenced by irrigation treatments and plastic mulch. Collected experimental data may contribute to designing an optimal irrigation program for a drip-irrigated intercropping field with plastic mulch.     

Solar radiation interception and canopy expansion of sweet corn in response to phosphorus

Insufficient phosphorus (P) availability decreases the yield of Zea mays, particularly for sweet corn crops grown in cool environments. This research examined the mechanisms of yield reductions with initial emphasis on canopy expansion processes that affect the interception of solar radiation. Experiments in two consecutive seasons (2001/2002 and 2002/2003) were grown at a low P site (Olsen P = 6 μg ml⁻¹) at Lincoln, New Zealand. Each experiment contained five rates of P application. In 2001/2002 rates of 0, 50, 100, 150, or 200 kg P ha⁻¹ were applied. In 2002/2003 an additional 0, 0, 10, 20 or 40 kg P ha⁻¹ was applied to the same plots producing total P treatments of 0, 50, 110, 170 or 240 kg P ha⁻¹ summed over the two seasons.When P availability was limited (0 or 50 kg P ha⁻¹) the rates of leaf tip and fully expanded leaf appearance were slower in both seasons. Phyllochrons (°Cd leaf tip⁻¹) were 5 °Cd longer in crops that received 0 kg P ha⁻¹ than those fertilised with ≥100 kg P ha⁻¹. The area of individual leaves was also reduced by low P inputs but the ranking of leaf area by main stem leaf position was conservative. The leaf area of the largest leaf of the unfertilised crops was at least 22% less than the maximum measured leaf area in both seasons. In contrast, P fertiliser application had no effect on leaf senescence.The rate of leaf appearance per plant, individual leaf area and plant population were integrated to calculate green leaf area index (GLAI) and to estimate accumulated radiation interception (RI_cum) for these crops. The total RI_cum throughout the season in the unfertilised crops was 12–28% less than for those crops that received ≥100 kg P ha⁻¹ in both seasons. This difference partly explained the differences in crop biomass production in response to P availability. A sensitivity analysis showed that RI_cum was equally sensitive to changes of the rate of leaf appearance and the area of individual leaves in response to P supply. Both processes need to be incorporated in mechanistic models of P effects on Z. mays which can be used to design efficient P fertiliser strategies.     

不同水氮处理对豫麦49-198籽粒抗氧化物含量的影响

2012-2013年度, 在温县和郑州大田条件下, 研究不同水氮处理对冬小麦品种豫麦49-198籽粒总酚、类黄酮、类胡萝卜素含量及抗氧化活性的影响。结果表明, 在施纯氮0~300 kg hm^–2范围内, 所有观测指标均随施氮量的增加而增加, 以施氮300 kg hm^–2处理最高。随灌水次数(0~2次)的增加, 总酚、类黄酮含量和抗氧化活性呈先增加后降低趋势, 以灌拔节水处理最高;类胡萝卜素含量在不同试点间表现不一致。水氮耦合, 以灌拔节水+施氮240~300 kg hm^–2处理的抗氧化物含量及抗氧化活性较高, 而总酚、类黄酮及类胡萝卜素的积累量则以灌拔节和开花水+施氮240~300 kg hm^–2处理较高。相关分析表明, 籽粒总酚、类黄酮含量与抗氧化活性均呈显著正相关, 表明总酚、类黄酮含量增加可以提高小麦籽粒抗氧化活性;不同深度土层土壤水分含量及硝态氮含量与籽粒抗氧化物质含量的相关性存在差异, 总体而言, 氮含量有助于总酚及类胡萝卜素含量的积累, 而水分含量可能有助于类黄酮含量的提高。     

Root decomposition at high and low N supply throughout a crop rotation

Soil nitrogen (N) dynamics can be modified by cover crops in rotations with cereals. Although, roots are a major source of N, little is known about the dynamics of root decomposition of cash and cover crops. The objective of this study was to assess the effects that cover crop species have on i) the decomposition of spring wheat roots during the growth of cover crops, and ii) the decomposition of cover crop roots during the growing season of spring wheat. The experiment aimed also at comparing three non-winter hardy cover crops of varying shoot C/N ratios under low and high N input levels of 6 and 12 g N m⁻² y⁻¹, respectively. The experiment included spring wheat (Triticum aestivum L.) as the main crop and non-winter hardy cover crops (yellow mustard (Sinapis alba L.), phacelia (Phacelia tanacetifolia Benth), and sunflower (Helianthus annuus L.) as well as bare soil fallow treatment. Minirhizotrons were used to non-destructively assess the spatial and temporal patterns of root growth and decomposition from 0.10 to 1.00 m. Simultaneously, we grew all crops in soil columns to measure destructively C and N content in the roots. We concluded that wheat root decomposition was not affected by cover crop species. In contrast, during the growing season of wheat root decomposition of yellow mustard was on average twice as high for phacelia and sunflower as a consequence of a higher production of roots with a significantly higher C/N ratio compared to the other cover crops.     

Response of giant reed (Arundo donax L.) to nitrogen fertilization and soil water availability in semi-arid Mediterranean environment

The aim of the present work was to evaluate the effect of soil water availability and nitrogen fertilization on yield, water use efficiency and agronomic nitrogen use efficiency of giant reed (Arundo donax L.) over four-year field experiment.After the year of establishment, three levels for each factor were studied in the following three years: I₀ (irrigation only during the year of establishment), I₁ (50% ETm restitution) and I₂ (100% ETm restitution); N₀ (0 kg N ha⁻¹), N₁ (60 kg N ha⁻¹) and N₂ (120 kg N ha⁻¹).Irrigation and nitrogen effects resulted significant for stem height and leaf area index (LAI) before senescence, while no differences were observed for stem density and LAI at harvest.Aboveground biomass dry matter (DM) yield increased following the year of establishment in all irrigation and N fertilization treatments. It was always the highest in I₂N₂ (18.3, 28.8 and 28.9 t DM ha⁻¹ at second, third and fourth year growing season, respectively). The lowest values were observed in I₀N₀ (11.0, 13.4 and 12.9 t DM ha⁻¹, respectively).Water use efficiency (WUE) was significantly higher in the most stressed irrigation treatment (I₀), decreasing in the intermediate (I₁) and further in the highest irrigation treatment (I₂). N fertilization lead to greater values of WUE in all irrigation treatment.The effect of N fertilization on agronomic nitrogen use efficiency (NUE) was significant only at the first and second growing season.Giant reed was able to uptake water at 160–180 cm soil depth when irrigation was applied, while up to 140–160 cm under water stress condition.Giant reed appeared to be particularly suited to semi-arid Mediterranean environments, showing high yields even in absence of agro-input supply.     

条带深松对不同密度玉米群体根系空间分布的调节效应

为探究条带深松耕作(SS)对密植玉米群体根系空间分布与容纳量的调节效应,本试验设置3个种植密度(低密：4.50万株 hm^-2、中密：6.75万株 hm^-2、高密：9.00万株 hm^-2),以土壤免耕(NT)为对照,利用小立方原位根土取样器,通过“3D monolith”根系空间取样方法,比较研究玉米个体与群体根系的空间分布对种植密度与土壤耕作方式的响应。结果表明,单株根长受种植密度影响显著,在0~50 cm土层中(每10 cm为一土层),高密种植的单株根长较低密种植减少110.31、43.18、15.73、10.49和17.45 m;在高密种植条件下,与土壤免耕比,条带深松耕作增加20~30 cm、30~40 cm、40~50 cm土层中的单株根长13.32%、19.80%、47.20%;单株根干重与单株根长的变化一致。种植密度对群体总根长的影响不显著,却显著影响群体根系的空间分布。与低密种植比,高密种植的植株中心根长密度在0~10 cm、10~20 cm土层中分别降低3.82 cm cm^-3、0.62 cm cm^-3,但植株之间的根长密度在0~10 cm、10~20 cm、20~30 cm、30~40 cm土层中分别增加1.13 cm cm^-3、0.18 cm cm^-3、0.06 cm cm^-3、0.05 cm cm^-3;在高密种植条件下对土壤进行条带深松耕作,与土壤免耕比,植株中心的根长密度在0~10 cm土层中降低16.10%,在10~20 cm、20~30 cm土层中却分别增加47.45%和13.37%,植株之间的根长密度在20~30 cm、30~40 cm、40~50 cm土层中分别增加50.26%、30.72%和106.15%;条带深松耕作显著提高密植玉米群体下层根系的容纳量。高密条件下条带深松耕作增加了群体根干重、深层根系量、植株间根系分布及根表面积,进而增加了地上部群体叶面积指数及地上部干重,最终促进产量显著提高。说明密植群体通过条带深松耕作改善了群体的根系空间分布,减弱了上层根系的拥挤,通过增加深层土壤根系量及植株之间根系量增加了群体根系容纳量,发挥了密植群体根系功能,实现了密植群体的高产。     

Water use efficiency among dry bean landraces and cultivars in drought-stressed and non-stressed environments

The agricultural use of water is higher than 85% in the western USA, resulting in an increasing water deficit in the region; this situation is commonly encountered throughout the world where irrigated and irrigation-assisted production systems are operational. The objective of this study was to examine differences among dry bean (Phaseolus vulgaris L.) landraces and cultivars in terms of water use efficiency (WUE), subsequently identifying those with a high water use efficiency. Six medium-seeded (25–40 g 100 seed wt⁻¹) landraces and cultivars of pinto and red market classes were evaluated in intermittent drought-stressed (DS) and non-stressed (NS) environments at Kimberly, Idaho, USA in 2003 and 2004. Each market class comprised one each of a landrace and old and new cultivars. Mean evapotranspiration (ET) in the NS environment was 384 mm in 2003 and 432 mm in 2004; the respective ET values in the DS environment were 309 and 268 mm. Mean seed yield was higher in the DS (2678 kg ha⁻¹) and NS (3779 kg ha⁻¹) environments in 2004 than in 2003 (688 and 1800 kg ha⁻¹, respectively). Under severe drought stress in 2003, WUE in the pinto bean ranged from 1.5 for the Common Pinto landrace to 4.4 kg ha⁻¹ mm⁻¹ water for cv. Othello. The Common Red Mexican landrace had the highest WUE (3.7), followed by cvs. NW 63 (2.8) and UI 259 (1.4) in the red market class. Under favorable milder climatic conditions in 2004, the mean WUE value was 10 kg ha⁻¹ mm⁻¹ water in the DS environment and 8.7 kg ha⁻¹ mm⁻¹ water in the NS environment. We conclude that dry bean landraces and cultivars with high WUE should be used to reduce dependence on irrigation water and to develop drought-resistant cultivars to maximize yield and WUE.     

Impact of Water Stress on Maize Grown Off-Season in a Subtropical Environment

During the last decade, the production of off‐season maize has increased in several regions of Brazil. Growing maize during this season, with sowing from January through April, imposes several climatic risks that can impact crop yield. This is mainly caused by the high variability of precipitation and the probability of frost during the reproduction phases. High production risks are also partially due to the use of cultivars that are not adapted to the local environmental conditions. The goal of this study was to evaluate crop growth and development and associated yield, yield components and water use efficiency (WUE) for maize hybrids with different maturity ratings grown off‐season in a subtropical environment under both rainfed and irrigated conditions. Three experiments were conducted in 2001 and 2002 in Piracicaba, state of São Paulo, Brazil with four hybrids of different maturity duration, AG9010 (very short season), DAS CO32 and Exceler (short season) and DKB 333B (normal season). Leaf area index (LAI), plant height and dry matter were measured approximately every 18 days. Under rainfed conditions, the soil water content in the deeper layers was reduced, suggesting that the extension of the roots into these layers was a response to soil water limitations. On average, WUE varied from 1.45 kg m⁻³ under rainfed conditions to 1.69 kg m⁻³ under irrigated conditions during 2001. The average yield varied from 4209 kg ha⁻¹ for the hybrids grown under rainfed conditions to 5594 kg ha⁻¹ under irrigated conditions during 2001. Yield reductions under rainfed conditions were affected by the genotype. For the hybrid DKB 333B with a normal maturity, yield was reduced by 25.6 % while the short maturity hybrid Exceler was the least impacted by soil water limitations with a yield reduction of only 8.4 %. To decrease the risk of yield loss, the application of supplemental irrigation should be considered by local farmers, provided that this practice is not restricted by either economic considerations or the availability of sufficient water resources.     

Long-term effects of N fertilization on cropping and growth of olive trees and on N accumulation in soil profile

Two experiments were conducted for 13 years in two olive groves of southern Spain to study the long-term effect of nitrogen (N) fertilization on trees and soil. In the first experiment, 12-year-old ‘Picual’ olive trees were arranged in a split plot design with method of N application (soil versus a 50% soil:50% foliar combination) as the whole plot factor, and amount of N applied annually (0, 0.12, 0.25, 0.5 or 1.0 kg N tree⁻¹) as the subplot factor. In the second experiment, N application to 50-year-old ‘Picual’ trees was based on the previous season's leaf N concentration. Urea was the source of N in both experiments. During the last 4 years, soil samples were taken at 0–20, 20–40, 40–60, 60–80, and 80–100 cm depth to evaluate the effect of N application on soil eutrophication. Fertilization with N had no significant effects on yield, fruit characteristics, and growth of olive trees for the 13 years of study, even when leaf N concentration increased with the amount of fertilizer N applied. Combining soil and foliar application may reduce the amount of fertilizer N necessary to correct a possible N deficiency because our experiments showed this practice to be more effective in increasing leaf N that applying N only to the soil. Our results question the established deficiency threshold of 1.4% of N in dried leaf because no reduction in yield or growth was observed for lower concentrations. However, leaf N concentration did not drop below 1.2% after 13 years with no N application, probably because of N inputs from rainfall and the mineralization of organic N. Whereas under natural conditions of the non-fertilized treatments NH₄⁺–N represented the dominant fraction of mineral N in soil, accumulation of high amounts of NO₃⁻–N in the soil profile occurred in the fertilized plots, which represents a high risk of N leaching from soil. All these results suggest that annual applications of fertilizer N are unnecessary to maintain high productivity and growth in olive. Applying N only when the previous season's leaf analysis indicates that leaf N concentration is below the deficiency threshold, is thus a recommended practice to optimize N fertilization in olive orchards and to reduce N losses by leaching.     

氮素对花铃期短期渍水棉花根系生长的影响

于2005—2006年在江苏南京农业大学卫岗试验站进行盆栽试验,设置正常灌水(土壤含水量为田间持水量的75%左右)和棉花花铃期土壤短期渍水处理(将正常灌水的棉花增加灌水至盆内有可见明水,持续8 d,然后用导管排除表面水层,使盆内土壤含水量逐渐恢复到田间持水量的75%左右),每个水分处理设置3个氮素水平(0、3.73、7.46 g N pot^-1,分别相当于大田0、240、480 kg N hm^-2),研究氮素对花铃期短期渍水棉花根系生长的影响。结果表明,在渍水处理结束时,与正常灌水处理相比,根干重和根冠比(R∶S)均降低;根系可溶性蛋白含量、超氧化物歧化酶(SOD)和过氧化氢酶(CAT)活性降低,过氧化物酶(POD)活性升高,丙二醛(MDA)含量升高;棉花根系活力和单株光合速率(CAP)显著降低。增加施氮可降低渍水棉花根系SOD活性,提高POD和CAT活性,以3.73 g N pot^-1(240 kg N hm^-2)施氮水平下的棉花根干物重最大,根系MDA含量最低,根系活力最强,单株光合速率(CAP)最高,相应籽棉产量最高。渍水停止15 d后,渍水棉花根系抗氧化酶活性和MDA含量与正常灌水处理的差异较小;施氮仍可提高棉花根系POD与CAT活性,降低MDA含量,增强根系活力,提高CAP。