Threshold of Soil Olsen-P in Greenhouses for Tomatoes and Cucumbers

Phosphorus (P) accumulation is a common phenomenon in greenhouse soil for vegetables. Excessive P accumulation in soil usually decreases the yield and quality of vegetables as well as potentially polluting water environments. Ninety-eight tomato and 48 cucumber greenhouses were investigated in the eight main vegetable production areas of Hebei Province, China. Soil Olsen-P, the electrical conductivity (EC), the pH value, the organic matter of the soil, and the cropping years of these greenhouses were investigated and analyzed in order to better understand the status of soil P accumulation and positively find effective ways to solve the excessive phosphate accumulation problem. The investigation showed that the ratio was above 70% for all of the greenhouses where the soil Olsen-P exceeded 90 mg·kg^?1 (upper bound of soil Olsen-P optimum value in greenhouse) in the 0–20 cm surface soil in the investigated greenhouses. There was a significant positive correlation between the soil Olsen-P content and the soil EC, between the soil Olsen-P and the cropping years, and the Olsen-P had a significant negative correlation with the soil pH value. It is concluded that supplying phosphate fertilizer excessively induced the soil EC to ascend and the pH value to descend, which increases the possibility of the soil secondary salinization and soil degeneration. The significant positive correlation between the soil organic content and the soil Olsen-P contents suggests that supplying organic fertilizer might mobilize soil residual phosphate. This also provides a good way to solve the problem of soil P accumulation. In order to further explore the threshold content of soil Olsen-P demanded by tomato and cucumber under the high soil Olsen-P condition, two tomato greenhouses (T1, T2) in Dingzhou and two cucumber greenhouses (C1, C2) in Wuqiang were researched. All of the greenhouses had ranges of soil Olsen-P content that were between 150 and 300 mg·kg^?1, which far exceeded the 90 mg·kg^?1 ideal. The P fertilizer application rates showed positive correlations with the soil Olsen-P contents and EC values in cucumber and tomato greenhouses in the current season. Analyzing T1 and T2 results showed that tomato was sensitive to the high soil Olsen-P contents ranging from 230.64 to 729.42 mg kg^?1 at the seedling stage (15 days after transplanting; DAT) and from 199.41 to 531.42 mg kg^?1 at the fruiting stage (90 DAT), because the yields correlated negatively with soil Olsen-P contents at each growth stage. It is suggested that the maximum soil Olsen-P threshold content for tomato should be lower than 230 mg·kg^?1 at the seedling stage and lower than 199 mg·kg^?1 at the fruiting stage. But cucumber yield did not change significantly as soil Olsen-P content rose from 248.75 to 927.62 mg kg^?1, 212.40 to 554.07 mg kg^?1, 184.48 to 455.90 mg kg^?1, and 128.42 to 400.96 mg kg^?1 at the seedling stage (15 DAT), early fruiting stage (50 DAT), middle fruiting stage (140 DAT), and late fruiting stage (235 DAT), respectively, suggesting that the maximal soil Olsen-P threshold content was lower than 249, 212, 185, and 128 mg·kg^?1 at each growth stage, respectively. The relationship between fruit qualities and soil Olsen-P contents at each growth stage was not evident. Activities of soil alkaline phosphatase (ALP) decreased as soil Olsen-P supply was raised in T1, T2, and C1 at the seedling stage. It is concluded that in an excess soil Olsen-P condition tomato yield decreases strongly as soil ALP activity decreases, whereas ALP activity has little direct effect on cucumber yield.     

Comparing Nutrient Availability in Low-Fertility Soils using Ion Exchange Resin Capsules

Assessing the nutrient status of low-input, low-fertility desert soils poses some unique challenges. Commonly used soil analysis procedures and resin capsules generally assess nutrient status of fertile agricultural soils. Ion-exchange resin capsules (Unibest Company, Bozeman, Mont.) provide a viable alternative. A study was conducted to determine effectiveness of resin capsules to extract low levels of nutrients applied to native soils. Loamy sand and sandy clay loam desert soils from Utah were treated with combinations of four rates of nitrogen (N) as ammonium nitrate (34–0–0), three rates of phosphorus (P) as phosphoric acid (0–72–0), and two rates of iron sulfate (FeSO₄·7H₂O) and zinc sulfate (ZnSO₄·7H₂O) (include an untreated control). Each soil treatment was implanted with a resin capsule placed into either 250 or 1000 cm³ of soil after addition of water equivalent to 50% field capacity and incubated for either 60 or 120 days at 25 °C. After the appropriate incubation time, capsules were washed and extracted using 2 M hydrochloric acid (HCl), and the extract was used to measure iron (Fe), ammonium (NH₄)-N, nitrate (NO₃)-N, sulfur (S), and zinc (Zn). Conventional soil tests were completed on incubated soils (60 or 120 days). Resin capsules reflected NH₄-N and P fertilizer applied at low rates in the loamy sand but not in the sandy clay loam. Neither Fe nor Zn application was reflected in resin capsules, but the accompanying S was clearly quantified. In comparison to conventional soil test procedures, resin capsule NH₄-N was clearly a better indicator than KCl-extractable NH₄-N; resin capsule NO₃-N was effective, but not as good an indicator as water extraction; and resin capsule P was reflective of soil applied P in loamy sand but not in sandy clay loam, whereas sodium bicarbonate was effective in both soils. Resin capsules show promise for use in low-input conditions, but additional understanding of interactions in variable soils is needed.     

Ureolytic Activity of Soybean and Corn Residue Extracts

The enzyme urease is responsible for the rapid hydrolysis of urea in agroecosystems where more than 50% of the applied nitrogen (N) can be lost via ammonia volatilization. The objectives of the study were to (1) extract urease from corn (Zea mays L.) and soybean (Glycine max L.) and (2) compare the urease activity from soybean and corn residues to Jackbean (Canavalia ensiformis) urease using Fourier transform infrared spectroscopy (FTI-R). Concentrations of urea and sodium bicarbonate ranging from 0 to 200 mM were analyzed with FTI-R to determine the correlation to peak height. Bicarbonate produced the most responsive peaks to concentration at 1,362 cm^?1. Urease extracted from soybean residue was active, producing a bicarbonate peak at 1362 cm^?1, whereas no urease activity was observed in corn residue. Variation among urease activities in crop residues could suggest a need for more precise nitrogen management in conservation tillage agroecosystems to reduce ammonia volatilization.     

Nitrogen effects on cantaloupes

Abstract

The NO₃ levels in cantaloupe (Cucumis melo L.) petioles relate closely to N treatment and reflect the N status of the cantaloupe plant. Suggested levels of petiole NO₃ in cantaloupes grown in Arizona are presented. Nitrogen treatment had little effect on melon size, earliness, or most storage quality factors that were evaluated except that deficiencies resulted in lower netting, poor general appearance and an increase in cull melons.     

Volumetric soil measures for routine soil testing

Abstract

The design, dimensiors and materials for constructing volumetric soil measures for routine soil testing use are presented. Scoop calibration techniques are also described. Reproducibility of results obtained under routine laboratory, conditions are shown. The measures include volumes of 1.0‐, 2.5‐, 5.0‐ and 10‐ cm³ respectively.     

几种保护性耕作措施在黄土高原旱作农田的实践

自2001年起,甘肃农业大学的研究者在甘肃省定西市安定区李家堡镇布设了不同保护性耕作措施下春小麦→豌豆和豌豆→春小麦轮作系统的定位试验,以研究免耕不覆盖(NT)、传统耕作秸秆还田(TS)、免耕秸秆覆盖(NTS)、传统耕作地膜覆盖(TP)和免耕地膜覆盖(NTP)等保护性耕作措施在黄土高原旱作农田生态系统中的效应。本文就近10年依托该试验获取的相关研究结果进行综述,重点阐述特定土壤、气候、农作制度下土壤理化性状、土壤微生物及其酶活性、土壤温室气体排放、作物生理生态等对上述几种保护性耕作措施的响应。初步得到免耕秸秆覆盖措施有助于形成良好的土壤结构、减少土壤侵蚀、改善土壤持水特性、提高土壤养分利用效率、改善土壤微生物区系、增强作物光合效能、增加作物产量等结论,对筛选出当地适宜的耕作模式、改善区域土壤质量、促进农业可持续发展有重要意义。在此基础上,提出目前该项研究存在的问题和今后重点关注的方向:1)保护性耕作土壤碳循环机理;2)覆盖方式的创新;3)温室气体排放测量方法的改进与完善。     

紫色土坡耕地氮素淋失通量的实测与模拟

氮淋失是氮素循环研究中最重要的环节之一,获得准确的氮淋失通量是当今农田氮循环研究中必不可少而又较为困难的工作之一。紫色土土层薄,土壤氮素难以蓄存,加之降水丰富,下伏透水性较弱的母岩,淋溶水达到母岩后难以垂直下渗而沿土壤岩石界面出流、汇流形成壤中流,紫色土氮素淋失主要表现为氮素随壤中流迁移流失。DNDC模型是基于过程的一种土壤碳氮循环模型,常用于农田温室气体排放模拟,但其应用于氮素淋溶的验证与测试不足。本文利用大型坡地排水采集器(lysimeter),测定紫色土坡耕地淋溶水量(壤中流流量)和氮素淋失通量,并利用观测数据对DNDC模型进行验证。结果表明,紫色土坡耕地小麦玉米季累积淋溶水通量为323.6 mm,径流系数33.3%,氮素淋失量为36.93 kg.hm 2,占全年氮素施用量的13.2%。壤中流流量与氮素淋失量实测值和模拟值的Pearson相关系数分别为0.944(P<0.05)和0.972(P<0.05),Theil不等系数分别为0.07和0.1,降雨量、土壤孔隙率和施氮水平是氮流失模拟的高敏感性参数。DNDC模型应用于紫色土坡耕地氮素淋失通量的模拟具有较高的可靠性,同时DNDC基于过程模型的优势可以描述持续降雨条件下的氮淋失过程,未来可通过进一步的验证,测试DNDC模型应用于氮淋失过程及区域氮淋失评估的可行性。     

横坡和顺坡耕作对紫色土土壤团聚体稳定性的影响

通过径流小区试验,分析探讨了紫色土横坡和顺坡两种耕作模式下表层(0~20 cm)土壤水稳性团聚体及有机碳含量的特征,为紫色土区坡耕地的有效改造和综合利用提供科学依据。试验结果表明,横坡耕作下土壤水稳性指数K值比顺坡耕作高38.99%,而土壤分散性D值为顺坡耕作的1.64倍,横坡耕作抗蚀性大于顺坡耕作。横坡耕作>0.25 mm水稳性团聚体含量比顺坡耕作增加3.62%,>5 mm、5~3 mm、3~2 mm水稳性团聚体含量横坡耕作均高于顺坡耕作,横坡耕作显著提高>2 mm水稳性团聚体含量。横坡耕作下团聚体结构体破坏率较顺坡耕作减少3.05%,团聚体平均重量直径为顺坡耕作的1.39倍。2种耕作模式下0.5~2 mm团聚体有机碳含量均最高,>0.25 mm不同粒级团聚体有机碳含量百分数均随粒径的减小而减小,均在0.5~0.25 mm粒级下达到最小。横坡和顺坡耕作模式下2~1 mm团聚体有机碳含量无显著差异。横坡耕作较顺坡耕作能够显著增加紫色土>2 mm水稳性团聚体含量,且对有机碳的固持作用更好,有利于土壤结构的改善。     

蜡样芽孢杆菌菌株X5强化的生物有机肥能有效控制根结线虫(Meloidogyne sp.)

The efficacy of Bacillus cereus X5 as a potential biological control agent against root-knot nematodes was evaluated in vitro by examining second-stage juvenile mortality and egg hatching rate under addition of culture filtrate and in planta by application of bio-organic fertilizers enhanced with B. cereus X5, B. thuringiensis BTG, or Trichoderma harzianum SQR-T037 alone or together in greenhouse and field experiments. The biofumigation of the root-knot nematode-infested soil with organic materials (chicken manure, pig manure and rice straw) alone or in combination with B. cereus X5 was also conducted in greenhouse experiments. In laboratory, the filtrate of B. cereus X5 more effectively reduced egg hatching rates during the incubation period for 14 d and more effectively killed the second-stage juvenile during the incubation period of 24 h than that of B. thuringiensis BTG. The highest dry shoot weights for greenhouse tomatoes and field muskmelons were found in both the treatment consisting of the bio-organic fertilizer enhanced with the three biocontrol agents and the treatment consisting of the bio-organic fertilizer enhanced only with B. cereus X5. The two bio-organic fertilizers achieved better nematicidal effects than those enhanced only with B. thuringiensis BTG or T. harzianum SQR-T037. B. cereus X5 also enhanced effect of biofumigation, which resulted in increased plant biomass and reduced nematode counts in the roots and rhizosphere soil. Therefore, these results suggested that biological control of root-knot nematodes both in greenhouses and fields could be effectively achieved by using B. cereus X5 and agricultural wastes.     

滩涂土壤有机碳空间分布与围垦年限相关性分析

中国具有治理和修复潜力的滨海滩涂盐土面积约为2000hm2。滨海滩涂盐土作为新成土壤,土体发育不明显、理化性状差、肥力水平低下。该文通过对东台境内表层土壤有机碳的采样分析,在ArcGIS地理信息系统及SPSS16.0系统平台上,利用地统计分析模块中的克里格法分析东台市表层土壤有机碳的空间变异规律,并分析不同滩涂围垦年限下表层土壤有机碳、总氮、pH值、EC1:5的变化特征及其相关关系,结果显示滨海表层土壤有机碳含量与总氮、围垦年限呈极显著正相关,相关系数r分别为0.959和0.749,与pH值、电导率EC1:5呈极显著负相关,相关系数r分别为-0.478和-0.649。围垦3a以上表层土壤有机碳可增加0.24%左右,总氮质量分数增加0.02%左右;围垦时间大于52a,有机碳质量分数自0.1%增加到1.6%,全氮质量分数自0.03%增加到0.12%,养分等级也相应从6级增加到3级。该文研究表明,滨海盐土随着围垦年限的增长,土壤碳储量与总氮含量随之增加、pH值与EC1:5随之降低,耕地质量也相应提高。