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.     

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.     

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