Can agroforestry improve soil fertility and carbon storage in smallholder banana farming systems?

Soil fertility depletion is a major constraint to agricultural production for smallholder farming households in many sub‐Saharan countries, and it is worsened by climate variability. In order to sustain food security for a growing population, measures have to be taken against C and nutrient losses from soils. This study examines whether banana–coffee agroforestry systems can improve soil fertility and C pools in smallholder farms in E Africa amidst observed climate variability. We selected 20 farms in Central Uganda, where soil samples were obtained from the top and subsoil layers. Samples were analyzed for several soil fertility parameters including soil organic matter (SOM), total soil organic C, pH, total N, plant‐available P, exchangeable K, texture, and bulk density. Soil C stocks were calculated based on soil organic C concentrations and bulky density. We measured tree diameter and height and calculated aboveground plant biomass using allometric equations. Belowground biomass was estimated using equations based on the respective aboveground plant biomass. Our results show that banana–coffee agroforestry farming systems had significantly higher total SOM and total N compared to the banana monoculture. Similar trends were observed for soil C stocks and total C pools. The former contained 1.5 times higher soil C stocks than the latter. Likewise, the mean total C pools for the banana–coffee agroforestry farm plots were 26% larger than that under banana monoculture. However, exchangeable K was higher in the soil of banana monocultures. Plant‐available P levels were limiting under both farming systems. The study demonstrates that beyond socio‐economic benefits banana–coffee agroforestry farming systems have beneficial effects on soil fertility and C sequestration compared to banana monocultures in the study area. However, precautions to avoid P depletion have to be taken under current climate conditions.     

勐海县甘蔗土壤养分空间分布特征及肥力评价

对勐海县10个甘蔗生产乡镇进行土壤调研取样,共采集0～20 cm土层样品200份,测定了土壤pH、有机质、碱解氮、有效磷、速效钾、交换性钙和交换性镁含量,运用ArcGIS的Kriging插值法分析了蔗区土壤肥力现状与空间分布特征,并采用改进后的Nemerow综合指数法评价了土壤的肥力等级.结果表明:勐海县蔗区土壤主要为...     

Effect of Long-Term Sugarcane (Saccharum Spp.) Cultivation on Chemical and Physical Properties of Soils in Belize

The sugarcane industry in Belize is one of the main economic drivers in the country and is therefore of crucial social and environmental importance. This study evaluated the degree of sustainability of commercial sugarcane production in Northern Belize by determining soil parameters (physical and chemical) in three soil layers (0–15, 15–30 and 30–50 cm) and crop profitability relative to years of sugarcane cultivation (4–25 years since land conversion). The parameters evaluated were organic matter (OM), total nitrogen (TN), cation exchange capacity (CEC), available phosphorus (P), potassium (K), pH, dry bulk density (DBD), porosity (?), and water-filled pore space (WFPS). Field interviews were conducted to document management practices, agricultural inputs, production costs, and yield. The results showed that OM and TN in all soil layers studied and CEC in the 30–50 cm layer decreased, and were negatively correlated, with years of sugarcane cultivation. This indicates that prolonged sugarcane cropping has detrimental effects on soil fertility. There was no clear pattern with years under sugarcane cultivation for P, pH, DBD, and K. Yield levels were maintained by intensification of cultivation, e.g. high inputs and regular replanting, providing short-term benefits at the expense of deterioration of soil fertility. The benefit to cost (B:C) ratio of sugarcane production in Northern Belize was marginal for American Sugar Refinery/Belize Sugar Industries (ASR/BSI), representative of intensive agriculture; and not profitable for small-scale farmers, 1.0 and 0.63 for plantation establishment and 1.2 and 1.0 average for the following six years of ratoon, respectively.     

Changes of chemical properties in an oxisol after clearing of native Cerrado vegetation for agricultural use in Vilhena, Rondonia State, Brazil

Native vegetation clearing in the Amazon Cerrado region for agricultural purposes may be modifying soil chemical characteristics. The extent of change depends on the management practices used. We evaluated changes in chemical properties of a clayey oxisol (dystrophic red yellow latosol) under no-tillage (NT) and conventional tillage (CT). Soil samples were taken randomly (n = 5) in July 2004 at 0–5 cm, 5–10 cm, 10–20 cm and 20–30 cm depths at six treatments: Cerrado with native vegetation, CT cultivated with rice for 1 year (1CT) and 2 years (2CT), and NT cultivated with soybean for 1 year (1NT), 2 years (2NT) and 3 years (3NT) in each case after a 2-year period of rice under CT. Soil pH (CaCl₂, KCl and water), ΔpH, total acidity (H⁺ + Al³⁺), total organic carbon (TOC), available P, exchangeable K, Ca, Mg, potential cation exchange capacity (CEC) and base saturation (V) were determined. The highest pH values were determined in topsoil layers at the older NT adoption. Under Cerrado pH was lower than under cultivation at all depths due to absence of lime application. Generally, negative values of ΔpH were observed at all sites in all layers indicating predominant presence of negative charges in the soil. Although not statistically significant it seems that the amount of negative charges was higher in deeper layers. Total acidity displayed the highest values throughout the soil profile under Cerrado and low pH and low concentrations of exchangeable bases. Cultivated systems with fertilizer generated considerable increases of P, K, Ca, and Mg compared to Cerrado. Soil macronutrient content and base saturation under NT gradually increased throughout the profile with time. Highest CEC values were calculated for the 0–5 cm and 5–10 cm layers under Cerrado and NT systems. For the 0–5 cm layer CEC was lower at the CT system compared to the Cerrado and the oldest year under NT system.

Alteration of TOC was more pronounced in the top 10 cm layer at all sites. The highest content was measured in the topsoil layer under Cerrado. Considering the future land use in Cerrado areas the NT system, if properly managed, appears to be the favourable management option of the existing croplands established after Cerrado clearing.     

Impact of sugarcane cultivation on soil carbon fractions, consistence limits and aggregate stability of a Yellow Latosol in Northeast Brazil

The effects of continuous sugarcane (Saccharum officinarum) cropping on the properties of a cohesive Yellow Latosol were studied in the region of the Coastal Tablelands, Northeast Brazil. Four areas were studied at Caeté mill, municipality of São Miguel dos Campos, Alagoas State, involving a native forest (Tn), and sugarcane fields cultivated for periods of 2 years (T2), 18 years (T18) and 25 years (T25). Samples were collected from each area at 0–0.2 and 0.2–0.4 m depth, to determine total organic C, physical fractionation of soil organic matter and consistence limits. Undisturbed samples were collected to determine wet aggregate mean weight–diameter, dry mean weight diameter and aggregate stability. In relation to the soil under native forest, total organic C and particulate organic matter contents were reduced after 2 years of cultivation. Sugarcane cropping for a longer period promoted a recuperation of soil organic matter content. The decrease of total organic C and reduction in aggregate stability and plastic limit after 2 years of sugarcane cultivation rendered the soil more susceptible to compaction.     

Nutrient concentrations and acidity in ferralitic soil under perennial cropping, fallow and primary forest in central Amazonia

The long‐term productivity on the acidic, nutrient‐poor upland soils of central Amazonia depends to a large extent on the chemical soil fertility as influenced by vegetation type and management. We compared soil and soil solution data from permanent cropping, fallow and primary forest on a Xanthic Ferralsol in central Amazonia to evaluate changes of soil fertility following forest conversion, agricultural use at different intensities and setting aside agricultural land. The agricultural systems included a perennial polyculture at two fertilizer inputs and a monoculture plantation. Soil and soil solution were collected to 2 m depth, and the soil solution was monitored over 2 years. Both soil and soil solution data showed decreasing soil fertility in the sequence: monoculture and polyculture at large input, polyculture at small input, forest and fallow. The soil solution data were more sensitive to effects of systems and fertilizer inputs on subsoil fertility. Fractionation of the N in the soil solution showed a larger proportion of dissolved organic N in the N‐poor fallow soil than in the soil under forest and agriculture. The soil under fallow, forest and low‐input agriculture had larger exchangeable acidity than that under high‐input agriculture, but the Al concentrations in the soil solution were very small because there were few cations with which to exchange and less nitrification. In high‐input agriculture, pronounced acidification peaks in the topsoil solution followed fertilization. The comparison of soil and soil solution data explained why the spontaneous vegetation thrives at very large exchangeable acidity in these soils, whereas agricultural systems often depend on liming to reduce the concentration of toxic Al in the soil.     

Soil chemical properties of an Indonesian red acid soil as affected by land use and crop management

In the middle terrace area of south Sumatra, Indonesia, where red acid soils poor in crop productivity are widely distributed, the effects of cropping pattern and cultivation techniques on physico-chemical properties of soil were investigated. Five patterns for cassava cropping, including monoculture, a rotation with annual food crops, and three intercroppings with differences in the combination with annual crops and in the planting density, were evaluated in Experiment I. In Experiment II, eight plots composed of the combinations of two tillage methods (no-tillage or conventional tillage), the presence or absence of surface mulch from crop residues, and two rates of chemical fertilizers were established for a maize–soybean–cowpea sequential cropping pattern. At the end of 3 years, there was no difference in total C and total N concentrations among the plots in Experiment I irrespective of the mulch treatment using crop residues. Soil organic matter (SOM) concentration was not affected even in the no-tillage plot where the maximum crop residues (20 t ha⁻¹) was given as surface mulch with the increased root residues due to higher rates of fertilizers (Experiment II). In Experiment I, available P concentration was highest in an intercropping with higher fertilizer rates and lowest cassava planting density. In Experiment II, an increase in available P was attained by mulching and the higher rate of fertilizers, and a minor positive effect of fertilizer was also observed in exchangeable Mg and K concentrations. Surface mulch resulted in less clay fraction compared with the non-mulch plots in both the experiments, suggesting its effect on the maintenance of soil particle distribution. An additional finding suggested no prominent influence of cassava monoculture on the level of SOM in this area based on the comparison with other major land uses, including secondary forest, rubber plantation, and mixed cultivation of fruits with crops. Nevertheless, the introduction of crop residue mulch and higher rates of fertilizers are recommended for sustaining soil quality and achieving higher crop yields.     

桂西北环境移民安置区新垦土地土壤质量与可持续利用研究——土壤肥力特征

本文对环江肯福环境移民安置示范区所采 88个表层土样及 4个剖面土样有机质 ,全氮 ,全磷 ,全钾 ,水解氮 ,速效磷 ,速效钾 ,pH等指标进行了测定。结果表明该区表层土壤有机质含量较高 ,土壤氮相对丰富 ,钾含量偏低 ,磷严重缺乏 ,pH偏酸性。土壤剖面发育完整 ,在土壤剖面中有机质、氮、速效磷、交换性钾主要聚集在 2 0cm的表层土壤中 ,全磷随深度的增加而降低 ,全钾和 pH值则随土壤深度增加而上升     

Arbuscular mycorrhizal fungi and soil aggregation in a no‐tillage system with crop rotation

Crop rotation adoption in no‐tillage systems (NTS) has been recommended to increase the biological activity and soil aggregation, suppress soil and plant pathogens, and increase the productivity aiming at the sustainability of agricultural areas. In this context, this study aimed to assess the effect of crop rotation on the arbuscular mycorrhizal fungi (AMF) community and soil aggregation in a soil cultivated for nine years under NTS. Treatments consisted of combinations of three summer crop sequences and seven winter crops. Summer crop sequences consisted of corn (Zea mays L.) monoculture, soybean (Glycine max L. Merrill) monoculture, and soybean–corn rotation. Winter crops consisted of corn, sorghum (Sorghum bicolor (L.) Moench), sunflower (Helianthus annuus L.), sunn hemp (Crotalaria juncea L.), pigeon pea (Cajanus cajan (L.) Millsp.), oilseed radish (Raphanus sativus L.), and millet (Pennisetum americanum (L.) Leeke). Soil samples were collected at a depth of 0–0.10 m for analyses of soil chemical, physical, and biological attributes. Spore abundance, total glomalin, and soil aggregate stability index were higher in the soil under corn monoculture. The highest values of aggregate mean weight diameter were observed in the soybean–corn rotation (3.78 mm) and corn monoculture (3.70 mm), both differing from soybean monoculture (3.15 mm), while winter crops showed significant differences only between sorghum (3.96 mm) and pigeon pea (3.25 mm). Two processes were identified in the soil under summer crop sequences. The first process was observed in PC1 (spore abundance, total glomalin, easily extractable glomalin, pH, P, and Mg²⁺) and was related to AMF; the second process occurred in PC2 (aggregate mean weight diameter, soil aggregate stability index, K⁺, and organic matter) and was related to soil aggregation. The nine‐year no‐tillage system under the same crop rotation adoption influenced AMF abundance in the soil, especially with corn cultivation in the summer crop sequence, which promoted an increased total external mycelium length and number of spores of AMF. In addition, it favored an increased soil organic matter content, which is directly related to the formation and stability of soil aggregates in these managements.     

Composition of organic C fractions in soils of different texture affected by sugarcane monoculture

ABSTRACT

Sugarcane is a strategic commodity in Indonesia. It is usually raised in a monoculture system. There is a lack of information about the effects of extended sugarcane monoculture on the soil carbon fraction. The aim of this study was to determine the relative changes in the soil organic C fractions in response to the duration of sugarcane monoculture on Entisols, Inceptisols, and Vertisols. The measured variables were the percentages of sand, silt, and clay, organic matter (OM), total nitrogen (TN), pH (H₂O), cation exchange capacity (CEC), NH₄ ⁺, NO₃ ^-, labile carbon fraction (soil carbon mineralization (C-Min), soil microbial carbon (C-Mic), and carbon particulate organic matter (C-POM)), and stable carbon fraction (humic and fulvic acids). Soil type with sugarcane monoculture period had significant influences on the percentages of clay, sand, silt, CEC, and pH (H₂O). Soil type and sugarcane monoculture period had no apparent significant effect on C-Min or C-POM but did significantly influence C-Mic. The humic and fulvic acid levels in all three soil types were affected by the duration of sugarcane monoculture. To establish the impact of long-term sugarcane monoculture on the physicochemical properties of soils with various textures, it is more appropriate to measure the soil stable carbon fractions such as humic and fulvic acid rather than the soil labile carbon fractions such as C-Min, C-POM, or C-Mic.     

我国中亚热带丘陵地区红壤的肥力恢复

There are about 1.27 million ha of upland red soils derived from Quaternary red clay facing the degradation in the low-hilly region of the middle subtropical China. From the aspects of chemistry, physics and microbiology, the processes of soil fertility restoration in the surface layer (0~20 cm) under three types of land use patterns (i.e. citrus orchard, tea garden and upland) in two provinces were studied in this work. Results showed that the reclamation of eroded waste land improved most of soil properties. Soil organic matter, total N and P, available P and K, and exchangeable Ca and Mg increased, but soil total K and exchangeable Al decreased. Soil pH decreased by 0.5 unit in the pure tea plantation for 20 years. Soil reclamation increased the percentage of soil microaggregates (<0.25 mm), especially those with a diameter of 0.02~0.002 mm. Soil total porosity increased in the cultivated lands with the increase of soil aeration and capillary porosity. The number of soil microorganisms increased with reclamation caused mainly by the huge increase of the total amount of bacteria. With the cultivation, the activity of soil urease and acid phosphatase increased, but that of invertase dropped.     

Assessment of soil quality monitoring indicators under long term rice cultivation in hot arid Ghaggar-flood plains of India

ABSTRACT

The evaluation of soil quality is essential in monitoring the long term effects of rice cultivation. Present study investigated the effects of long term rice cultivation on soil properties and organic C pools and identified indicators for monitoring soil quality in Ghaggar-flood plains of hot arid India. Soil samples were collected from fields with 0, 10, 20, 30 and 40 years of rice cultivation. The study revealed that electrical conductivity (EC) and exchangeable sodium percentage (ESP) increased after 30–40 years of rice cultivation. Available nutrients increased with increasing years of rice cultivation. The organic carbon pools namely, total organic carbon (TOC), Walkley Black carbon (WBC) and particulate organic carbon (POC) were increased above 50% in 20 and above years of rice cultivation. The TOC and POC were increased by 40.6 to 132.4% and 31.7% to 104.8% in 10 to 40 years of rice cultivation. Cation exchange capacity, WBC, ESP and CaCO₃ could serve as soil monitoring indicators of long term rice cultivation in arid region. The findings clearly indicated that long term rice cultivation could aggravate soil salinity and have negative impact on soil quality in arid environment.     

No-till effects on organic matter, pH, cation exchange capacity and nutrient distribution in a Luvisol in the semi-arid subtropics

No-till (NT) system for grain cropping is increasingly being practised in Australia. While benefits of NT, accompanied by stubble retention, are almost universal for soil erosion control, effects on soil organic matter and other soil properties are inconsistent, especially in a semi-arid, subtropical environment. We examined the effects of tillage, stubble and fertilizer management on the distribution of organic matter and nutrients in the topsoil (0–30 cm) of a Luvisol in a semi-arid, subtropical environment in southern Queensland, Australia. Measurements were made at the end of 9 years of NT, reduced till (RT) and conventional till (CT) practices, in combination with stubble retention and fertilizer N (as urea) application strategies for wheat (Triticum aestivum L.) cropping.

In the top 30 cm depth, the mean amount of organic C increased slightly after 9 years, although it was similar under all tillage practices, while the amount of total N declined under CT and RT practices, but not under NT. In the 0–10 cm depth, the amounts of organic C and total N were significantly greater under NT than under RT or CT. No-till had 1.94 Mg ha⁻¹ (18%) more organic C and 0.20 Mg ha⁻¹ (21%) more total N than CT. In the 0–30 cm depth, soil under NT practice had 290 kg N ha⁻¹ more than that under the CT practice, most of it in the top 10 cm depth. Microbial biomass N was similar for all treatments. Under NT, there was a concentration gradient in organic C, total N and microbial biomass N, with concentrations decreasing from 0–2.5 to 5–10 cm depths.

Soil pH was not affected by tillage or stubble treatments in the 0–10 cm depth, but decreased significantly from 7.5 to 7.2 with N fertilizer application. Exchangeable Mg and Na concentration, cation exchange capacity and exchangeable Na percentage in the 0–10 cm depth were greater under CT than under RT and NT, while exchangeable K and bicarbonate-extractable P concentrations were greater under NT than under CT.

Therefore, NT and RT practices resulted in significant changes in soil organic C and N and exchangeable cations in the topsoil of a Luvisol, when compared with CT. The greater organic matter accumulation close to the soil surface and solute movement in these soils under NT practice would be beneficial to soil chemical and physical status and crop production in the long-term, whereas the concentration of nutrients such as P and K in surface layers may reduce their availability to crops.     

Soil degradation and management under intensive sugarcane cultivation in North Queensland

Abstract. Sugarcane yields in the Herbert Valley in North Queensland have been declining over the past 15 years. Better yields are obtained where crops are grown on previously unused land. Soils under cane are more compacted, more acid, contain less organic matter and are lower in cation exchange capacity and exchangeable cations. These differences reflect soil degradation caused by intensive cultivation.
Contributing factors to the degradation of soils include soil compaction and structural breakdown occurring during harvest and cultivation operations, losses of organic matter due to burning of crop residues and acidification of soils due to large applications of nitrogen fertilizers.
Soil management practices should aim to increase soil organic matter levels, provide a more favourable biological environment, reduce physical damage to soils during harvesting and cultivation, reduce soil acidity and improve the effectiveness of fertilizing practices.     

A comparison of soil degradation under smallholder farming and large-scale irrigation land use in Kano State,Northern Nigeria

Changes in soil properties under two land use types: smallholder farms and large-scale irrigated agriculture were investigated over a period of 13 and 14 years respectively using the following parameters: particle size distribution, soil pH, exchangeable cations, cation exchange capacity, total organic carbon and nitrogen and total and available potassium and phosphorus. Results indicate that more adverse changes took place in soils under large-scale irrigation than in those under smallholder farms during the periods under consideration. Agricultural sustainability is more likely to be achieved for smallholder farms than for large-scale irrigation where soil degradation resulting from loss of fine soil particles through erosion can be a serious hindrance to long-term land use. In order to achieve agricultural sustainability in Kano State, it is recommended that chemical fertilizers be incorporated into the smallholder farming system, while the adoption of suitable soil conservation practices would make the large-scale irrigation systems more stable and sustainable.     

Soil organic matter quality as influenced by tillage,lime, and phosphorus

In Eastern Canada, cereal yields are often restricted by soil acidity and low fertility. Continuous cereal production can also lead to soil structural degradation. The addition of lime and fertilizers and the adoption of conversation tillage practices are proposed solutions which may have a positive impact on soil quality. The objective of the present work was to assess the impact of 3 years of different tillage practices and P additions, and of a single lime addition on organic C and total N, microbial biomass C, and on N mineralization at the surface layer (0–7.5 cm) of a Courval sandy clay loam (Humic Gleysol). The easily mineralizable N, total amount of N mineralized in 22.1 weeks, the rate of N mineralization, and microbial biomass C were significantly greater in the minimum tillage than in the moldboard plow treatment. Chisel plow treatment showed intermediate values. The ratios of potentially mineralizable N and of easily mineralizable to total soil N were also significantly larger under minimum tillage and chisel plowing than under moldboard plowing. The lime and P treatments had no significant effect on the measured soil quality parameters. The total amount of N mineralized per unit of biomass C decreased as the tillage intensity increased, suggesting a decrease in the efficiency of the biomass in transforming organic N into potentially plant-available forms and thus a loss in soil organic matter quality. The results of this study indicate that conservation tillage practices such as rototilling and chisel plowing are efficient ways of maintaining soil organic matter quality when old pastures are brought back into cultivation.     

Applications of reduced tillage in hills of central Nepal

Conventional tillage practices on steep and fragile landscape of Himalayan hills result in significant loss of topsoil during rainy season. Soil erosion in Nepal mid-hills is the most critical during pre-monsoon season. Many reviews argue that reduced tillage could be an option to tackle this problem. However, very few field experiments to evaluate reduced tillage systems have to date been conducted in this region. Thus, a field experiment was initiated in factorial randomized complete block design on acidic sandy loam soil (Lithic Dystochrept) during the summer season of 2001 at Kathmandu University (1500 masl) to assess the effects of tillage and cropping patterns on soil and nutrient losses, crop yield and soil fertility. Two main treatments viz. conventional and reduced till, and two sub-treatments viz. sole maize (Zea mays) and maize + soybean (Glycine max) were considered. Soil organic carbon (OC), total nitrogen (N), plant available phosphorus (P) and exchangeable potassium (K) were determined for the original soil and eroded sediment using standard methods. Two years of data indicated annual soil and nutrient losses to be significantly lowered by reduced till as compared to conventional till. Total annual soil loss from conventional and reduced till was 16.6 and 11.1 Mg/ha, respectively. Similarly, annual nutrient losses associated with the eroded sediment were 188 kg OC/ha, 18.8 kg N/ha, <1 kg P/ha and 3.8 kg K/ha for conventional till and 126 kg OC/ha, 11.8 kg N/ha, <1 kg P/ha and 2.4 kg K/ha for reduced till. Soil OC and N losses were significantly higher in conventional till and this may be one of the major causes of fertility depletion in the Nepalese hills. Soil chemical properties did not differ due to tillage and cropping systems; however, over years pH, N and P were increased irrespective of treatments. Although treatments were at par for maize grain yield, conventional till + soybean produced highest grain yield (4.0 Mg/ha) followed by reduced till + soybean (3.9 Mg/ha) and conventional till sole maize (3.8 Mg/ha). Mixed cropping of legumes and maize do not help conserve soil and nutrient loss in hills of central Nepal. Thus, reduced till could be a viable option for minimizing soil and nutrient losses without sacrificing economic yields in central hills of Nepal.     

热带农业生态系统土壤肥力与植物养分综合管理研究进展

The greatest challenge for tropical agriculture is land degradation and reduction in soil fertility for sustainable crop and livestock production.Associated problems include soil erosion,nutrient mining,competition for biomass for multiple uses,limited application of inorganic fertilizers,and limited capacity of farmers to recognize the decline in soil quality and its consequences on productivity.Integrated soil fertility management(ISFM) is an approach to improve crop yields,while preserving sustainable and long-term soil fertility through the combined judicious use of fertilizers,recycled organic resources,responsive crop varieties,and improved agronomic practices,which minimize nutrient losses and improve the nutrient-use efficiency of crops.Soil fertility and nutrient management studies in Ethiopia under on-station and on-farm conditions showed that the combined application of inorganic and organic fertilizers significantly increased crop yields compared to either alone in tropical agro-ecosystems.Yield benefits were more apparent when fertilizer application was accompanied by crop rotation,green manuring,or crop residue management.The combination of manure and NP fertilizer could increase wheat and faba bean grain yields by 50%–100%,whereas crop rotation with grain legumes could increase cereal grain yields by up to 200%.Although organic residues are key inputs for soil fertility management,about 85% of these residues is used for livestock feed and energy;thus,there is a need for increasing crop biomass.The main incentive for farmers to adopt ISFM practices is economic benefits.The success of ISFM also depends on research and development institutions to provide technical support,technology adoption,information dissemination,and creation of market incentives for farmers in tropical agro-ecosystems.     

长期稻虾共作模式提高稻田土壤生物肥力的机理

  【目的】  长期稻虾共作是提高稻田肥力的有机生态途径。研究该模式对稻田土壤有机碳库和土壤酶活性的影响,为该模式的可持续应用提供理论依据。  【方法】  基于连续10年 (2005—2015) 中稻单作和稻虾共作的田间定位试验,于2015年10月中旬水稻收获后,按照0—10 cm、10—20 cm、20—30 cm、30—40 cm 土层采集土样,分析不同土层中总有机碳 (total organic carbon,TOC)、土壤微生物量碳 (microbial biomass carbon,MBC)、可溶性有机碳 (dissolved organic carbon,DOC)、易氧化有机碳 (easily-oxidized organic carbon,EOC) 和颗粒有机碳 (particulate organic carbon,POC) 含量,测定不同土层土壤水稳性团聚体中有机碳的含量,计算了土壤碳库管理指数,同时分析了与土壤碳、氮和磷代谢有密切关系的纤维素酶、蔗糖酶、脲酶和酸性磷酸酶活性。  【结果】  1) 相对于中稻单作,稻虾共作显著增加了各土层中TOC、POC和DOC含量,增加30—40 cm土层中MBC含量以及10—40 cm土层中EOC含量;2) 稻虾共作显著提高了10—30 cm土层中土壤碳库管理指数,碳库管理指数在10—20 cm和20—30 cm土层中较中稻单作模式分别提高了52.7%和58.2%;3) 稻虾共作模式下,0—20 cm土层中小于0.053 mm粉–黏团聚体的有机碳含量显著高于中稻单作模式,而在20—30 cm土层各粒级团聚体的有机碳含量均显著高于中稻单作模式;4) 与中稻单作相比,稻虾共作土壤脲酶活性在10—20 cm土层显著降低了16.7%,而在20—30 cm土层纤维素酶活性显著提高了28.0%;5) 除DOC外,TOC、POC、MBC与纤维素酶、蔗糖酶、脲酶和酸性磷酸酶活性均呈显著正相关。  【结论】  长期稻虾共作提高了稻田土壤有机碳及其活性组分含量,特别是提高了20—30 cm土层纤维素酶活性,促进了根茬等有机物的分解,提高了该层次各粒级团聚体内的有机碳含量,改善了土壤结构,加大了水稻根系的下扎深度,改善了固持速效养分的能力,从而提升了稻田土壤生物肥力。     

Loss of soil organic matter and related soil properties under long-term sugarcane production on two contrasting soils

The effects of increasing periods under sugarcane monoculture (managed with preharvest burning) on soil organic matter content and related soil properties were investigated in the 0- to 10-cm layer of a sandy coastal Ochric Cambisol (Glenrosa soil) and a red Rhodic Ferralsol (Hutton soil) from the sugar belt of the South African province of KwaZulu-Natal. The organic C content at both sites under undisturbed vegetation was between 40 and 50 g C kg^-1. This declined exponentially with increasing years under sugarcane. For the Glenrosa site it reached a new equilibrium level after about 30-40 years. After 20-30 years of sugarcane, organic C content had declined to about 33 g kg^-1 for the Hutton soil and 17 g kg^-1 for the Glenrosa soil. The higher organic matter content maintained at the Hutton site was attributed mainly to clay protection of organic matter since the clay content of the Hutton soil was 62% compared to 18% for the Glenrosa soil. For the same reason, aggregate stability was also generally higher in the Hutton than Glenrosa soil. The loss of soil organic matter under sugarcane resulted in a concomitant decline in soil microbial biomass C, percentage of organic C present as microbial biomass, basal respiration, fluorescein diacetate hydrolytic activity and aggregate stability. At the Glenrosa site, the natural '¹³C abundance in soils was used to calculate the loss of forest-derived, native soil C and the concomitant input of sugarcane-derived C. Sugarcane-derived organic C increased over time until it accounted for about 61% of organic C in the surface 10 cm in soils that had been under sugarcane for greater than 50 years. It was concluded that sugarcane production can cause a large decline in soil organic matter content and that practices such as green cane harvesting, zero tillage and use of green crops should be promoted to help ameliorate the problem.