黄土高原旱地轮作与施肥长期定位试验研究 Ⅱ.土壤酶活性与土壤肥力

本文分析了长期试验土壤酶活性与土壤有机C、全N、有效P含量、主要微生物类群之间的关系。相关分析表明,土壤脲酶、碱性磷酸酶、蛋白酶活性随土壤有机C含量的增加而增加,蔗糖酶、过氧化氢酶活性与有机C之间的关系因施肥种类及种植方式的不同而不同;微生物数量仅真菌与脲酶、蛋白酶活性之间的相关性达到显著水平。除过氧化氢酶外,其它4种酶的活性均与当年种植冬小麦处理的产量存在显著相关关系。利用主成分分析与通径分析揭示了土壤酶活性与养分之间的内在关系及酶活性对土壤养分的影响。根据主成分分析结果,旱地土壤肥力状况用脲酶、碱性磷酸酶、蛋白酶活性作为综合评价指标优于过氧化氢酶与蔗糖酶。     

Tillage effects on microbial biomass and nutrient distribution in soils under rain-fed corn production in central-western Mexico

Quantifying how tillage systems affect soil microbial biomass and nutrient cycling by manipulating crop residue placement is important for understanding how production systems can be managed to sustain long-term soil productivity. Our objective was to characterize soil microbial biomass, potential N mineralization and nutrient distribution in soils (Vertisols, Andisols, and Alfisols) under rain-fed corn (Zea mays L.) production from four mid-term (6 years) tillage experiments located in central-western, Mexico. Treatments were three tillage systems: conventional tillage (CT), minimum tillage (MT) and no tillage (NT). Soil was collected at four locations (Casas Blancas, Morelia, Apatzingán and Tepatitlán) before corn planting, at depths of 0–50, 50–100 and 100–150 mm. Conservation tillage treatments (MT and NT) significantly increased crop residue accumulation on the soil surface. Soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were highest in the surface layer of NT and decreased with depth. Soil organic C, microbial biomass C and N, total N and extractable P of plowed soil were generally more evenly distributed throughout the 0–150 mm depth. Potential N mineralization was closely associated with organic C and microbial biomass. Higher levels of soil organic C, microbial biomass C and N, potential N mineralization, total N, and extractable P were directly related to surface accumulation of crop residues promoted by conservation tillage management. Quality and productivity of soils could be maintained or improved with the use of conservation tillage.     

旱地长期定位施肥土壤剖面中有效硫累积及其影响因素

对设在黄土高原旱地黑垆土上不同N、P配比与用量的长期定位试验土壤剖面有效硫的分布与累积进行了研究。结果表明 ,长期施用不同量及不同配比的尿素与过磷酸钙肥料 ,对土壤剖面有效硫的含量影响明显 ,无硫投入的处理CK、N2、N4剖面有效硫含量低 ,平均分别为 7.73、10 .6 4、12 .16mg/kg ,分布均匀 ,而有硫投入的处理有效硫在剖面形成累积峰 ,最大含量可达 95.42mg/kg。大量的硫素随过磷酸钙施入土壤之后 ,部分以可溶无机硫酸盐形式被下渗水淋溶到土体的深层累积 ,累积量随施硫量的增加而增加 ,由于投入硫量大 ,在同一硫水平上 ,产量随氮肥用量增加而增加 ,但累积硫的量减少不多。石灰性土壤有效硫的下淋累积受作物、土壤、施肥、降水等多种因素影响 ,是长期的累积过程     

Short-term changes in nitrogen availability, gas fluxes (CO2, NO, N2O) and microbial biomass after tillage during pasture re-establishment in Rondônia, Brazil

Anthropogenic conversion of primary forest to pasture for cattle production is still frequent in the Amazon Basin. Practices adopted by ranchers to restore productivity to degraded pasture have the potential to alter soil N availability and N gas losses from soils. We examined short-term (35 days) effects of tillage prior to pasture re-establishment on soil N availability, CO₂, NO and N₂O fluxes and microbial biomass C and N under degraded pasture at Nova Vida ranch, Rondônia, Brazilian Amazon. We collected soil samples and measured gas fluxes in tilled and control (non tilled pasture) 12 times at equally spaced intervals during October 2001 to quantify the effect of tillage. Maximum soil NH₄⁺ and NO₃⁻ pools were 13.2 and 6.3 kg N ha⁻¹ respectively after tillage compared to 0.24 and 6.3 kg N ha⁻¹ in the control. Carbon dioxide flux ranged from 118 to 181 mg C–CO₂ m² h⁻¹ in the control (non-tilled) and from 110 to 235 mg C–CO₂ m² h⁻¹ when tilled. Microbial biomass C varied from 365 to 461 μg g⁻¹ in the control and from 248 to 535 μg g⁻¹ when tilled. The values for N₂O fluxes ranged from 1.22 to 96.9 μg N m⁻² h⁻¹ in the tilled plots with a maximum 3 days after the second tilling. Variability in NO flux in the control and when tilled was consistent with previous measures of NO emissions from pasture at Nova Vida. When tilled, the NO/N₂O ratio remained <1 after the first tilling suggesting that denitrification dominated N cycling. The effects of tilling on microbial parameters were less clear, except for a decrease in qCO₂ and an increase in microbial biomass C/N immediately after tilling. Our results suggest that restoration of degraded pastures with tillage will lead to less C matter, at least initially. Further long-term research is needed.     

Soil fertility properties on Agave angustifolia Haw. plantations

This study examined the variations in soil physical, chemical and biological properties from Agave angustifolia fields in three sites with different topographic conditions (valley, hill and mountain), in Oaxaca, Mexico, associated with the tillage systems, disk ploughing (DP), animal drawn ploughing (ADP) and minimum tillage (MT), respectively. Plant ages were 1.5–3.5 years (class 1), 3.6–5.5 years (class 2) and 5.6–7.5 years (class 3). Soil samples were taken at two soil depths (0–20 and 21–40 cm) from plots of 4000 m² within each site and plant age classes, during the spring of 2005. The main changes in soil properties were found in the mountain site. Soil bulk density (2.0 g cm⁻³), cone penetration resistance (CPR) (3.96 MPa), 0.7 and 1.0 mm water stable aggregates (WSA) (28.3 g kg⁻¹ and 102.2 g kg⁻¹, respectively) were higher in the mountain site than in the hill and valley fields. This result is consistent with the rocky substrate beneath the shallow soil. Soil organic carbon (SOC) (23.9 g kg⁻¹), available N (23.1 mg kg⁻¹) and soil microbial biomass carbon (SMBC) (969.6 μg g⁻¹) at the mountain site showed the highest values, suggesting that MT practiced in this topographic condition favours the organic matter accumulation and biological activity. Soil microbial biomass carbon and SOC seem to be the soil properties that were mainly affected by the sites and soil management associated with them. For the three sites, SOC, P_Olsen, available N, exchangeable Na⁺ and SMBC were higher at 0–20 cm depth than at 21–40 cm depth within each site. Exchangeable Ca²⁺ and K⁺, P_Olsen and CPR increased with plant age. In contrast, available N decreased. Soil chemical properties were more affected by the age of the plant than physical and biological properties. Results reported here represent a reference of the fertility properties of soils cultivated with A. angustifolia, which could be used in further studies focused on management and tillage systems.     

Fungal biomass in pastures increases with age and reduced N input

Previous studies have shown that soil fungal biomass increases towards more natural, mature systems. Shifts to a fungal-based soil food web have previously been observed with abandonment of agricultural fields and extensification of agriculture. In a previous field experiment we found increased fungal biomass with reduced N fertilisation. Here, we explore relationships between fungi, bacteria, N input and grassland age on real dairy farms in the Netherlands. We hypothesised that also in pastures that are still in production there is a negative relationship between fungal biomass and fertilisation, and that fungal biomass increases with grassland age in pastures that are still in production. We expected the fungal/bacterial biomass ratio to show the same responses, as this ratio has often been used as an indicator for management changes. We sampled 48 pastures from eight organic dairy farms. Sites differed in age and fertilisation rate. We determined fungal and bacterial biomass, as well as ergosterol (a fungal biomarker). Fungal and bacterial biomass and ergosterol, showed a negative relationship with N application rate, and correlated positively with organic matter percentage. In old pastures, fungal biomass and ergosterol were higher than in younger pastures. Because bacterial biomass responded in the same way as fungal biomass, the F/B ratio remained constant, and can therefore—in our data set—not be used as an indicator for changing management. We conclude that the changes in fungal and bacterial biomass were driven by changes in organic matter quality and quantity. The negative relationship we found between N application rate and fungal biomass adds to earlier work and confirms the presence of this relationship in pastures with relatively small differences in management intensities. Earlier studies on shifts in fungal biomass focused on ex-agricultural fields or restoration projects. Here we show that fungal biomass is also higher in older agricultural pastures.     

Energy and water balance measurements for water productivity analysis in irrigated mango trees, Northeast Brazil

Crop water parameters, including actual evapotranspiration, transpiration, soil evaporation, crop coefficients, evaporative fractions, aerodynamic resistances, surface resistances and percolation fluxes were estimated in a commercial mango orchard during two growing seasons in Northeast Brazil. The actual evapotranspiration (E_a) was obtained by the eddy covariance (EC) technique, while for the reference evapotranspiration (E₀); the FAO Penman–Monteith equation was applied. The energy balance closure showed a gap of 12%. For water productivity analysis the E_a was then computed with the Bowen ratio determined from the eddy covariance fluxes. The mean accumulated E_a for the two seasons was 1419 mm year⁻¹, which corresponded to a daily average rate of 3.7 mm day⁻¹. The mean values of the crop coefficients based on evapotranspiration (K_c) and based on transpiration (K_cb) were 0.91 and 0.73, respectively. The single layer K_c was fitted with a degree days function. Twenty percent of evapotranspiration originated from direct soil evaporation. The evaporative fraction was 0.83 on average. The average relative water supply was 1.1, revealing that, in general, irrigation water supply was in good harmony with the crop water requirements. The resulting evapotranspiration deficit was 73–95 mm per season only. The mean aerodynamic resistance (r_a) was 37 s m⁻¹ and the bulk surface resistance (r_s) was 135 s m⁻¹. The mean unit yield was 45 tonne ha⁻¹ being equivalent to a crop water productivity of 3.2 kg m⁻³ when based on E_a with an economic counterpart of US$ 3.27 m⁻³. The drawback of this highly productive use of water resources is an unavoidable percolation flux of approximately 300 mm per growing season that is detrimental to the downstream environment and water users.     

Improving wood volume predictions in dry tropical forest in the semi-arid Brazil

The volumetric variability of dry tropical forests in Brazil and the scarcity of studies on the subject show the need for the development of techniques that make it possible to obtain adequate and accurate wood volume estimates. In this study, we analyzed a database of thinning trees from a forest management plan in the Contendas de Sincorá National Forest, southwestern Bahia State, Brazil. The data set included a total of 300 trees with a trunk diameter ranging from 5 to 52 cm. Adjustments, validation and statistical selection of four volumetric models were performed. Due to the difference in height values for the same diameter and the low correlation between both variables, we do not suggest models which only use the diameter at breast height (DBH) variable as a predictor because they accommodate the largest estimation errors. In comparing the best single entry model (Hohenald-Krenn) with the Spurr model (best fit model), it is noted that the exclusion of height as a predictor causes the values of 136.44 and 0.93 for Akaike information criterion (AIC) and adjusted determination coefficient (R2 adj), which are poorer than the second best model (Schumacher-Hall). Regarding the minimum sample size, errors in estimation (root mean square error (RMSE) and bias) of the best model decrease as the sample size increases, especially when a larger number of trees with DBH≥15.0 cm are randomly sampled. Stratified sampling by diameter class produces smaller volume prediction errors than random sampling, especially when considering all trees. In summary, the Spurr and Schumacher-Hall models perform better. These models suggest that the total variance explained in the estimates is not less than 95%, producing reliable forecasts of the total volume with shell. Our estimates indicate that the bias around the average is not greater than 7%. Our results support the decision to use regression methods to build models and estimate their parameters, seeking stratification strategies in diameter classes for the sample trees. Volume estimates with valid confidence intervals can be obtained using the Spurr model for the studied dry forest. Stratified sampling of the data set for model adjustment and selection is necessary, since we find significant results with mean error square root values and bias of up to 70% of the total database.     

Exploiting chemical ecology to manage hyperparasitoids in biological control of arthropod pests

Insect hyperparasitoids are fourth trophic level organisms that commonly occur in terrestrial food webs, yet they are relatively understudied. These top‐carnivores can disrupt biological pest control by suppressing the populations of their parasitoid hosts, leading to pest outbreaks, especially in confined environments such as greenhouses where augmentative biological control is used. There is no effective eco‐friendly strategy that can be used to control hyperparasitoids. Recent advances in the chemical ecology of hyperparasitoid foraging behavior have opened opportunities for manipulating these top‐carnivores in such a way that biological pest control becomes more efficient. We propose various infochemical‐based strategies to manage hyperparasitoids. We suggest that a push‐pull strategy could be a promising approach to ‘push’ hyperparasitoids away from their parasitoid hosts and ‘pull’ them into traps. Additionally, we discuss how infochemicals can be used to develop innovative tools improving biological pest control (i) to restrict accessibility of resources (e.g. sugars and alternative hosts) to primary parasitoid only or (ii) to monitor hyperparasitoid presence in the crop for early detection. We also identify important missing information in order to control hyperparasitoids and outline what research is needed to reach this goal. Testing the efficacy of synthetic infochemicals in confined environments is a crucial step towards the implementation of chemical ecology‐based approaches targeting hyperparasitoids. © 2019 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.