Nitrogen uptake and partitioning under alternate- and every-furrow irrigation

Alternate-furrow irrigation, combined with fertilizer placement in the non-irrigated furrow, has the potential to reduce fertilizer leaching in irrigated corn (Zea mays L.). The potential also exists, however, for reduced N uptake under alternate-furrow irrigation. This study examined the effects of fertilizer placement and irrigation treatment on N uptake, rootashootroot circulation, and partitioning between reproductive and vegetative tissues. Rainfall was above average in both years of the study, especially during May and June, so that root growth beneath the non-irrigated furrow was equal to root production beneath the irrigated furrow. Under those conditions, soil NO₃ concentration in the fertilized furrow during late-vegetative and reproductive growth was greater in the alternate-furrow compared with the every-furrow treatment, resulting in increased fertilizer N uptake during reproductive growth and increased N partitioning to reproductive tissues under alternate-furrow irrigation. About 80% of the fertilizer N found in roots had first been translocated to the shoot and then returned via the phloem to the root system. Nitrogen cycling from root to shoot to root was not affected by irrigation treatment. Alternate-furrow irrigation successfully increased N uptake and reduced the potential for NO₃leaching when environmental conditions allowed adequate root development in the non-irrigated furrow, and when the growing season was long enough to allow the crop to reach physiological maturity.     

A Global Meta-Analysis on the Impact of Management Practices on Net Global Warming Potential and Greenhouse Gas Intensity from Cropland Soils

Little is known about management practices that can simultaneously improve soil and environmental quality and sustain crop yields. The effects of novel and traditional management practices that included a combination of tillage, crop rotation, and N fertilization on soil C and N, global warming potential (GWP), greenhouse gas intensity (GHGI), and malt barley (Hordeum vulgarie L.) yield and quality were examined under non-irrigated and irrigated cropping systems from 2008 to 2011 in eastern Montana and western North Dakota, USA. In loamy soil under non-irrigated condition in eastern Montana, novel and traditional management practices were no-till malt barley-pea (Pisum sativum L.) with 80 kg N ha^-1 and conventional till malt barley-fallow with 80 kg N ha^-1, respectively. In sandy loam soil under irrigated and non-irrigated conditions in western North Dakota, novel and traditional management practices included no-till malt barley-pea with 67 (non-irrigated) to 134 kg N ha^-1 (irrigated) and conventional till malt barley with 67 (non-irrigated) to 134 kg N ha^-1 (irrigated), respectively. Compared with the traditional management practice, soil organic C (SOC) and total N (STN) at 0–120 cm were 5% greater with the novel management practice under non-irrigated condition in eastern Montana and under irrigated condition in western North Dakota, but were not different under non-irrigated condition in western North Dakota. In both places under irrigated and non-irrigated conditions, total applied N rate, residual soil NO₃-N content at 0–120 cm, global warming potential (GWP), and greenhouse gas intensity (GHGI) were 15 to 70% lower with the novel than the traditional management practice. Malt barley yield and quality were not different between the two practices in both places. Novel management practices, such as no-till malt barley-pea with reduced N rate_, can simultaneously enhance soil and environmental quality, reduce N input, and sustain crop yield compared with traditional practices in the northern Great Plains, USA.     

隔沟交替灌溉条件下玉米根系形态性状及结构分布

为揭示根系对土壤环境的适应机制,研究了隔沟交替灌溉条件下玉米根系形态性状及结构分布。以垄位和坡位的玉米根系为研究对象,利用Minirhizotrons法研究了根系（活/死根）的长度、直径、体积、表面积、根尖数和径级变化及其与土壤水分、土温和水分利用效率（WUE）的相关关系。结果表明,对于活根,在坡位非灌水区域复水后根系平均直径减小,而根系日均生长速率、单位面积土壤根系体积密度、根尖数和表面积均增大,并随灌水区域土壤水分的消退逐渐减小;对于死根,在坡位非灌水区域复水后根系日均死亡速率、根系体积密度、根尖数和表面积变化均减小,其中根系死亡速率和死根直径随土壤水分的消退逐渐降低,而死根体积密度、根尖数和表面积分布随土壤水分降低呈增大趋势;在垄位,根系形态分布趋势与坡位一致,除根系直径与与坡位比较接近外,其他根系形态值均小于坡位。将根系分成4个径级区间分析根系的形态特征,结果表明在根系长度和体积密度分布中以2.5－4.5 mm径级的根系所占比例最大,在根尖数和根系表面积分布中以0.0－2.5 mm径级的根系为主。通过显著性相关分析,死根直径、体积密度、活根表面积等根系形态与土壤含水率、土壤温度和WUE间均存在显著或极显著的正相关关系,部分根系形态指标（如根系的生长速率、活根体积密度）只与坡位土壤含水量、土壤温度具有明显的相关性,表明隔沟交替灌溉对坡位根系形态的调控作用比垄位显著。     

Agronomic Considerations for Sweet Sorghum Biofuel Production in the South-Central USA

Sweet sorghum (Sorghum bicolor (L.) Moench) is currently recognized throughout the world as a highly promising biomass energy crop. Production systems and management practices for sweet sorghum have not been fully developed for the USA, although sporadic research efforts during recent decades have provided some insights into production of sweet sorghum primarily for fermentable sugar production. Field plot experiments were conducted at sites across Louisiana to assess biomass and sugar yield responses to N fertilizer, plant density, and selected cultivars. Although linear increases in stem biomass production and fermentable sugar yield were obtained with increasing N fertilizer rate under irrigated conditions, most of the increase was from the initial 45 kg N ha⁻¹ increment. Nitrogen fertilization increased stem biomass production but not fermentable sugar yield in some non-irrigated environments. Increased plant density contributed to fermentable sugar yield only under growth-limiting conditions, particularly under limited soil moisture. Location effects indicate that sweet sorghum may not be suitable for some sub-optimal cropland and pasture environments in Louisiana. During the primary growing season, cultivar did not affect fermentable sugar yields, although Dale was consistently high in sugar concentration during this period. Nitrogen fertilizer increased fermentable sugar yields only when moisture was not limiting. Overall results indicate that in environments where soil moisture limits plant growth, sugar yield responses are likely from increased plant density and not from increased N fertilization.     

Long‐term biochar application promotes rice productivity by regulating root dynamic development and reducing nitrogen leaching

Biochar is beneficial for improving soil quality and crop productivity. However, the long‐term effects of biochar addition on temporal dynamics of plant shoot and root growth, and the changes in soil properties and nitrogen (N) leaching are still obscure. Here, based on a long‐term (7 years) biochar field experiment with rice in northwest China, we investigated the effects of two biochar rates (0 and 9 t ha^?1 year^?1) and two N fertilizer rates (0 and 300 kg N ha^?1 year^?1) on shoot and root growth, root morphology, N leaching, and soil physicochemical properties. The results showed that both biochar and N fertilizer significantly promoted rice growth, with their interaction significant only in some cases. Both fertilizers enhanced rice shoot biomass and N accumulation in various growth stages as well as increased grain yield. Nitrogen fertilizer significantly promoted root growth regardless of biochar application. However, biochar application without N fertilizer increased root biomass and length during the whole growth period, except in the booting stage; biochar with N application promoted root growth at tillering, reduced root biomass but maintained root length with low root diameter and high specific root length during the jointing and booting stages, and then delayed root senescence in the grain filling stage. Long‐term applications of biochar and N fertilizer reduced 10%–12% bulk density of topsoil compared to the control treatment with no N fertilizer and no biochar. Long‐term biochar application also improved soil total organic carbon and concentrations of available N, phosphorus, and potassium. In addition, biochar and N fertilizer applied together significantly reduced nitrate and ammonium concentration in leachate at different soil depths. In conclusion, biochar could regulate root growth, root morphology, soil properties, and N leaching to increase rice N fertilizer‐use efficiency.     

Effects of partial root-zone irrigation on hydraulic conductivity in the soil-root system of maize plants

Effects of partial root-zone irrigation (PRI) on the hydraulic conductivity in the soil-root system (L(sr)) in different root zones were investigated using a pot experiment. Maize plants were raised in split-root containers and irrigated on both halves of the container (conventional irrigation, CI), on one side only (fixed PRI, FPRI), or alternately on one of two sides (alternate PRI, APRI). Results show that crop water consumption was significantly correlated with L(sr) in both the whole and irrigated root zones for all three irrigation methods but not with L(sr) in the non-irrigated root zone of FPRI. The total L(sr) in the irrigated root zone of two PRIs was increased by 49.0-92.0% compared with that in a half root zone of CI, suggesting that PRI has a significant compensatory effect of root water uptake. For CI, the contribution of L(sr) in a half root zone to L(sr) in the whole root zone was ～50%. For FPRI, the L(sr) in the irrigated root zone was close to that of the whole root zone. As for APRI, the L(sr) in the irrigated root zone was greater than that of the non-irrigated root zone. In comparison, the L(sr) in the non-irrigated root zone of APRI was much higher than that in the dried zone of FPRI. The L(sr) in both the whole and irrigated root zones was linearly correlated with soil moisture in the irrigated root zone for all three irrigation methods. For the two PRI treatments, total water uptake by plants was largely determined by the soil water in the irrigated root zone. Nevertheless, the non-irrigated root zone under APRI also contributed to part of the total crop water uptake, but the continuously non-irrigated root zone under FPRI gradually ceased to contribute to crop water uptake, suggesting that it is the APRI that can make use of all the root system for water uptake, resulting in higher water use efficiency.     

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

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

不同灌溉方式对玉米根毛生长发育的影响

在盆栽条件下,采用分根装置,在光学显微镜和电子显微镜下对均匀灌水、固定部分根区灌水和根系分区交替灌水3种方式下各1/2根区的根毛发育状况进行观察并采样照相,研究不同根区根毛的生长发育特征.结果表明：处理40 d时,固定部分根区灌水条件下,非灌水区的根毛有明显退化脱落现象,退化区所占比例为20.96%,明显大于其他根区;灌水区的根系发黄,有腐烂斑,且根分枝有退化现象,根毛密集区的密集程度不如非灌水区,但根毛退化区所占比例小（15.72%）,退化程度轻.均匀灌水根系的根毛发育状况与固定灌水的灌水区类似.交替灌水条件下,先灌水区和后灌水区根毛密集区的密集程度均较高,根毛退化脱落区分别占9.77%和10.38%,明显小于均匀灌水和固定灌水.说明采用交替灌水方式可促进根系根毛的生长发育,而持续湿润或干燥不利于根系根毛的生长发育.     

根区湿润方式对玉米根系生长发育的影响

将厚塑料紧密地固定在盆栽试验用桶壁和底的中央,玉米种子播种于厚塑料布的正上方,在均匀灌水、固定部分根区灌水和根系分区交替灌水3种方式下,分期测定两个1／2根区根系的长度、面积、干重以及单位面积的平均根长和比根长,研究不同根区根系的生长发育特征。结果表明,处理40d时,与其他根区相比,固定灌水非灌水区的比根长和单位面积平均根长明显增大,说明土壤水分减少使根系直径变小。根面积、长度以及干重的增长速率均表现为,处理0～5d内,与均匀灌水及其非灌水区相比,两种局部灌水的灌水区均显著增大;处理10～15d内,交替灌水的灌水区较其他根区明显增大,固定灌水的灌水区与均匀灌水相近。固定灌水时,灌水区根系的面积、长度、干重及其增长速率较之非灌水区显著增大;交替灌水时,两个根区的增长速率呈交替变化,其绝对数值随时间延长趋于相同。表明交替灌水不仅可刺激供水区根系的补偿生长,而且对恢复供水区也有补偿效应,并能够促使不同根区的根系均衡发展。     

Turnover of residual 15N-labelled fertilizer N in soil following harvest of oilseed rape (t Brassica napus L.)

We studied the fate of ¹⁵N-labelled fertilizer nitrogen in a sandy loam soil after harvest of winter oilseed rape (Brassica napus L. cv. Ceres) given 100 or 200 kg N ha^-1 in spring, with or without irrigation. Our main objective was to quantify the temporal variations of the soil mineral N, the extractable soil organic N and soil microbial biomass N, and fertilizer derived N in these pools during autumn and winter. Nitrogen use efficiency of the oilseed rape crop varied from 47% of applied N in the 100N, irrigated treatment to 34% in the 200N, non-irrigated treatment. However, only in the latter treatment did we find significantly higher fertilizer derived soil mineral N than in the three other treatments which all had low soil mineral N contents at the first sampling after harvest (8 days after stubble tillage). Between 31% and 42% of the applied N could not be accounted for in the harvested plants or 0-15 cm soil layer at this first sampling. Over the following autumn and winter none of the remaining fertilizer derived soil N was lost from the 0–5 cm depth, but from the 5–15 cm depth a marked proportion of N derived from fertilizer was lost, probably by leaching. Negligible amounts of fertilizer derived extractable soil organic and mineral N (<1 kg N ha^-1, 0-15 cm) were found in all treatments after the first sampling.Soil microbial biomass N was not significantly affected by treatments and showed only small temporal variability (±11% of the mean 76 kg N ha^-1, 0- 15 cm depth). Surprisingly, the average amount of soil microbial biomass N derived from fertilizer was significantly affected by the treatments, with the extremes being 5.5 and 3.1 kg N ha^-1 in the 200N, non-irrigated and 100N, irrigated treatments, respectively. Also, the estimated exponential decay rate of microbial biomass N derived from fertilizer, differed greatly (2 fold) between these two treatments, indicating highly different microbial turnover rates in spite of the similar total microbial biomass N values. In studies utilising ¹⁵N labelling to estimate turnover rates of different soil organic matter pools this finding is of great importance, because it may question the assumption that turnover rates are not affected by the insertion of the label.     

Tracer studies on the balance and chemical distribution of applied nitrogen under different moisture regimes using lysimeter

Summary Tracer studies were made on balance and chemical distribution of added fertilizer under field conditions using a modified type of lysimeter at different moisture regimes. A modified chemical method was also used for the determination of different forms of organic N.An average of 25 per cent of the isotope enriched nitrogen applied to soil could not be accounted for at the end of the 3 years of experiment. The amount of residual added N in soil was around 33 per cent of which 27 per cent was in 0–20 cm layers and only 6 per cent was found in 20–50 cm layers. The average crop recoveries were around 43 per cent. Only 0.18 per cent of NO₃–N was leached from the irrigated plots.The alkali-stable N (amino acid-N) fraction was higher for irrigated (19 per cent) than nonirrigated plots (15 per cent). There were no difference in the amounts of fixed NH₄, non-hydrolyzed and alkali-labile N fractions for irrigated and non-irrigated plots. Only an average of 1.5 per cent of total fertilizer N was found as fixed NH₄–N form but the total fixed NH₄–N was higher (10–13 per cent) than that reported by other workers for surface soil layers. The sum of different soil-nitrogen fractions were always higher than the total nitrogen in soil.     

半干旱地区膜垄和土垄的集雨效率和不同集雨时期土壤水分比较

于 2 0 0 2年 4月～ 8月在兰州大学干旱农业生态榆中试验站进行研究 ,在平地上形成沟垄相间的微地形 ,采用 3种沟垄比和两种下垫面材料 ,垄作为径流区 ,沟作为集水区 (沟内不种任何作物 )。采用平均产流率法分析了不同垄型集水面的集水效率 ,结果表明 ,膜垄的平均集水效率为 90 % ,土垄的平均集水效率为 16 .8% ;通过对不同垄型集水面垄中、沟边、沟中的土壤水分进行比较发现 ,对于膜垄在集雨的各个时期沟中的土壤含水量高于垄中 ,沟边的土壤含水量介于沟中和垄中土壤含水量两者之间。如 7月 14日测定 ,沟中、沟边和垄中 0～ 2 0 0 cm土层土壤平均含水量分别为 10 .39%、10 .2 4 %和 9.4 2 % ;对于土垄 ,在集雨前期和集雨中期 ,沟中和沟边的土壤含水量相差不大 ,沟中和沟边的土壤含水量均低于垄中的土壤含水量 ,表现出和膜垄完全不一样的特性 ,如 7月 14日测定 ,沟中、沟边和垄中 0～ 12 0 cm土层土壤平均含水量分别为 8.98%、8.6 8%和 10 .0 3% ,在集雨后期 ,沟边和沟中的土壤含水量大于垄中土壤含水量 ,如 8月 13日测定 ,沟中、沟边和垄中 0～ 12 0 cm土层土壤平均含水量分别为 9.76 % A、9.38% B和 7.94 % C,该试验表明土垄在集雨后期 ,在集雨和土壤水分分配方面表现出和膜垄的相似的特性     

Temporal and spatial profiling of root growth revealed novel response of maize roots under various nitrogen supplies in the field

A challenge for Chinese agriculture is to limit the overapplication of nitrogen (N) without reducing grain yield. Roots take up N and participate in N assimilation, facilitating dry matter accumulation in grains. However, little is known about how the root system in soil profile responds to various N supplies. In the present study, N uptake, temporal and spatial distributions of maize roots, and soil mineral N (N(min)) were thoroughly studied under field conditions in three consecutive years. The results showed that in spite of transient stimulation of growth of early initiated nodal roots, N deficiency completely suppressed growth of the later-initiated nodal roots and accelerated root death, causing an early decrease in the total root length at the rapid vegetative growth stage of maize plants. Early N excess, deficiency, or delayed N topdressing reduced plant N content, resulting in a significant decrease in dry matter accumulation and grain yield. Notably, N overapplication led to N leaching that stimulated root growth in the 40-50 cm soil layer. It was concluded that the temporal and spatial growth patterns of maize roots were controlled by shoot growth and local soil N(min), respectively. Improving N management involves not only controlling the total amount of chemical N fertilizer applied, but also synchronizing crop N demand and soil N supply by split N applications.     

Key processes of the nitrogen cycle in an irrigated and a non-irrigated grazed pasture

The paper presents integrated measurements of N fixation, net mineralisation, pasture yield and change in soil mineral N over a 12 month period for dairy pastures on a sandy loam soil in the South East of South Australia. The two adjacent pastures studied were an irrigated perennial white clover-ryegrass and an annual non-irrigated subterranean clover with mixed annual grasses. This produced the most comprehensive mineral N balance reported for grazed pastures, to the authors' knowledge, allowing calculation of gaseous and leaching losses of N (210 kg ha^–1 in the irrigated and paddock and 81 kg ha^–1 in the non irrigated paddock) primarily from urine patches. In both paddocks these losses were about three times the N yield in milk (61 and 28 kg N ha^–1 respectively) and were replenished by biological N fixation (294 and 100 kg N ha^–1). However, mineralisation of soil organic N, excretal N and pasture residues (687 and 438 kg N ha^–1) was the major source of mineral N for cycling and losses. The results demonstrate the enormous impact of pasture management on N fluxes and reinforce the importance of livestock urine on the magnitude of N fluxes including gaseous and leaching losses.     

根区交替控制灌溉条件下玉米根系吸水规律

为了阐明根区交替控制灌溉(CRDAI)条件下玉米根系吸水规律,通过田间试验,在沟灌垄植模式下采用根区交替控制灌溉研究玉米根区不同点位(沟位、坡位和垄位)的根长密度(RLD)及根系吸水动态。研究表明,根区土壤水分的干湿交替引起玉米RLD的空间动态变化,在垄位两侧不对称分布,并存在层间差异;土壤水分和RLD是根区交替控制灌溉下根系吸水速率的主要限制因素。在同一土层,根系吸水贡献率以垄位最大,沟位最低;玉米营养生长阶段,10—30 cm土层的根系吸水速率最大;玉米生殖生长阶段,20—70 cm为根系吸水速率最大的土层,根系吸水贡献率为43.21%—55.48%。研究阐明了交替控制灌溉下根系吸水与土壤水分、RLD间相互作用的动态规律,对控制灌溉下水分调控机理研究具有理论意义。     

Decline of Globodera rostochiensis as Influenced by Potato Root Diffusate Movement and Persistence in Soil

Decline of Globodera rostochiensis populations occurring naturally in soil and those added to potato hills and furrow centers in nylon bags was correlated with root weight of Hudson, Rosa, and Katahdin potatoes at two locations in New York. Cysts in bags were added to soil at planting and at 1, 3, 5, 7, and 9 weeks after emergence (AE). Fallow decline required only 2-4 weeks in soil and did not increase with time. Decline due to growing potatoes was greater in hills than in furrow centers, and resistant Hudson potatoes stimulated greater nematode hatch for longer times in both hills and furrows than did resistant Rosa and susceptible Katahdin. Potato root diffusate (PRD) was produced in highest concentration early in the season; decreased egg hatch with time was probably the result of declining PRD production and inactivation of PRD in soil. Decreasing potato row spacing from 92 cm to 46 and 23 cm between rows increased G. rostochiensis decline in furrow centers, with the majority of decline occurring within 1-3 weeks AE. Replanting potatoes after 1 week of trap crop growth failed to favor population reduction over a single full season crop.     

The phenology of fine root growth in a maple-dominated ecosystem: relationships with some soil properties

A two-year study was undertaken in a maple-dominated watershed of southern Québec, Canada, to examine relationships between trends in fine root growth, stem diameter growth, soil moisture, soil temperature, mineralized-N and extractable-P. Until September, soil temperature was consistently higher in 1995 than in 1994. Apart from the first sampling in mid-May, soil moisture was higher in 1994 than in 1995. In 1994, most fine roots were produced before leaf expansion, whereas in 1995, fine root production peaked in July. Annual fine root production was estimated to be 2.7 times higher in 1994 than in 1995. Stem growth was strongly associated with the seasonal and annual variation in soil temperature. Root and diameter growth were asynchronous in 1994 but not in 1995. Fine root production was associated with two groups of variables: a soil fertility (mineralized-N and extractable-P) group and a physical soil environment (moisture and temperature) group. Our results are consistent with the negative effect of high soil-N fertility on fine root production but are inconclusive as to the positive effect of high soil-P fertility. Soil conditions that are detrimental to root growth such as high N availability and anaerobiosis could modify the normal dynamics of fine root growth.     

Water deficit, root demography, and the causes of internal blackening in field-grown tomatoes:(Lycopersicon esculentum Mill.)

An internal blackening disorder may cause substantial losses in the value of tomatoes grown for processing. The disorder resembles an internal form of blossom-end rot and appears to be more common in dry seasons. In an experiment to test whether the internal blackening is caused by water deficit and whether it is indeed blossom-end rot, plots of cv. Cannery Row were irrigated to keep the soil moisture deficit <50 mm and others were sheltered from rain and not irrigated from early flowering onwards. Shoot growth (total and fruit dry mass) was measured destructively at intervals, and root growth and death nondestructively using minirhizotrons. There was a greater incidence of internal blackening and blossom-end rot, and lower Ca concentrations, in the fruit of non-irrigated plants. Root growth and root death were accelerated in these plants around the time that internally-blackened fruit were set. Although the internal blackening syndrome shared some features with blossom-end rot some differences were apparent in this experiment. It is suggested that internal blackening could have resulted from increased root competition for photosynthate, leading to abnormal seed development. Root turnover was appreciable (30–40% of the roots survived 28 days). This suggests there may be substantial errors in contemporary models of dry matter partitioning in tomato crops.     

Whey utilization in furrow irrigation: effects on aggregate stability and erosion

Improving soil structure often reduces furrow erosion and maintains adequate infiltration. Cottage cheese whey, the liquid byproduct from cottage cheese manufacture, was utilized to stabilize soil aggregates and reduce sediment losses from furrow irrigation. We applied either 2.4 or 1.9L of whey per meter of furrow (3.15 or 2.49Lm(-2), respectively) by gravity flow without incorporation to two fields of Portneuf silt loam (Durinodic Xeric Haplocalcid) near Kimberly, ID. Furrows were irrigated with water beginning four days later. We measured sediment losses with furrow flumes during each irrigation and measured aggregate stability by wet sieving about 10 days after the last irrigation. Overall, whey significantly increased aggregate stability 25% at the 0-15mm depth and 14% at 15-30mm, compared to controls. On average, whey reduced sediment losses by 75% from furrows sloped at 2.4%. Whey increased the aggregate stability of structurally degraded calcareous soil in irrigation furrows.     

水肥异区交替灌溉对夏玉米生理指标的影响

以夏玉米品种‘户单4号'为材料,通过防雨棚内微区试验研究了两种灌水量(450 m~3/hm~2和900 m~3/hm~2)条件下水肥异区交替灌溉和均匀灌溉对夏玉米生长以及某些生理指标的影响.结果显示:(1)在节水50%的条件下,水肥异区交替灌溉与高灌水量均匀灌溉的夏玉米生物量、产量均无显著差异.(2)低灌水量时,水肥异区交替灌溉下的玉米根系伤流液、叶片可溶性蛋白含量、硝酸还原酶活性、光合速率、蒸腾速率等均高于均匀灌溉施肥处理,而植株全氮含量及叶片水分利用效率与均匀灌溉施肥的差异不显著.(3)高灌水量时,水肥异区交替灌溉处理除根系活力、光合速率以及蒸腾速率高于均匀灌溉处理外,其他指标均低于后者.研究表明,在低灌水量条件下,水肥异区交替灌溉能使夏玉米保持较高的根系活力和正常生理代谢,提高其叶片水分利用效率,从而达到了节水增产的目的.