Long-Term Soil Ecosystem Studies

Changes in topsoil C content were measured in 60 experiments on soddy-podzolic soils in the Russian Federation, Belarus, Ukraine, Lithuania and Latvia with different management characteristics. The data were compiled with a range of actual climatic parameters for the years of the experiments. The combined impact of different management practices (inorganic fertilizers, organic manure and different rotations), climate gradients and soil properties (initial soil C, clay content) was analysed using a static model. The importance of initial C level interactions with the soil and climatic variables are demonstrated as one of the major factors of soil organic matter (SOM) dynamics. The effect of different treatments for seven long-term experiments at the same site (Barybino, theMoscow Region) was explored using both static and dynamic modeling approaches. The SUNDIAL dynamic model was used to estimate the dynamics of different C pools for the whole 35-year experimentation period. Some adjustments to parameters were necessary to obtain satisfactory results. The management practices tested lead to changes not only in total SOM but also in SOM quality parameters. This was established using a complex of chemical and biological methods. For cropping systems with 50% of row crops manure application increased steady state C values by about 0.2%. High inorganic N fertilization decreased the steady state C values. The negative effect of high inorganic N fertilization was seen to be more pronounced on soil with a higher C content. This influence might be a result of increased organic C mineralization after autumn application of mineral N where there may be no crop present to utilize the fertilizer, resulting in adverse changes in SOM quality. The mineral fertilization contributes significantly to the formation of labile humic substances at the expense of Ca-forms of SOM which are more resistant to microbial decomposition and act as the binding agents of aggregate stability.

Productivity of grain crops and grazed pastures inevitably declines without soil nutrient replacement and may eventually make these enterprises unprofitable. We monitored these declines in north-eastern Australia during 23 years after clearing 2 of 3 adjacent brigalow catchments, in order to define the productivity levels of developed brigalow land over time. One catchment (11.7 ha) was used for grain production and another (12.7 ha) for beef production from a sown buffel grass pasture. There was no upward or downward trend in annual rainfall amounts throughout the study period. In the cropped catchment, grain yield from 14 winter crops without added nutrients declined significantly in 20 years from 2.9 to 1.1 t/ha.year on the upper-slope clay soil (92 kg/ha.year) and from 2.4 to 0.6 t/ha.year on the Sodosol (88 kg/ha.year). Crop production per year declined by 20% between 2 successive 10-year periods. Wheat grain protein content also declined with time, falling below the critical value for adequate soil N supply (11.5%) 12 years after clearing on the Sodosol and 16 years after clearing on the clay soil. Such declines in grain quantity and quality without applied fertiliser reduce profitability. The initial pasture dry matter on offer of 8 t/ha had halved 3 years after clearing, and a decline in cattle liveweight gain of 4 kg/ha.year was observed over an 8-year period with constant stocking of 0.59 head/ha. Due to fluctuating stocking rate levels of 0.3–0.7 head/ha over the trial period, liveweight productivity trends are attributed to the multiple effects of stocking rate changes and fertility decline. The amount of nitrogen exported from the cleared catchments was 36.1 kg/ha.year in grain but only 1.6 kg/ha.year in cattle (as liveweight gain). Total soil N at 0–0.3m declined by 84 kg/ha.year under cropping but there was no significant decline under grazing. The soil nutrients removed during grain and beef production need to be replaced in order to avert productivity decline post-clearing

Crop–pasture rotations (CPR) are unusual around the world but have been the predominant cropping system in Uruguay since the 1960s. Uruguay has a temperate sub-humid climate, 80% of its landscape (16 Mha) is climax grasslands C3 and C4 species. Beef, wool, and dairy are the main commodities. Crops occupy a portion of the remaining 20% land area, primarily on Argiudolls and Vertisols, rotated with seeded grass and legume pastures. Continuous cropping (CC) with conventional tillage (CT) has proven unsustainable due to decreased soil productivity. Seeded pasture periods increased soil productivity. CPR adoption created less variable inter-annual economic results, but soil degradation remained a major concern during the crop cycle using CT. Farmers and technicians became interested in no-till (NT) to reduce erosion and production cost. Currently, approximately 52% of crop producing farms and 25% of dairy farms have adopted NT. This paper synthesizes research results (mainly from long-term experiments) contrasting CC versus CPR with CT (1960–1990) and NT (from 1990). Soil erosion was reduced more than six times with NT in CC, and almost three times in CPR compared with CC using CT; but combining the use of CPR and NT resulted in the same low erosion rate as under natural pasture. The transition from CT to NT is not always easy. The time between herbicide application to pasture and planting of the first crop of the rotation crop cycle with NT is a critical transition factor to optimize N and water availability, and soil tilth. Chiseling or paraplowing can alleviate plow-pans inherited by NT from previous CT; but higher soil strength at the soil surface under NT contributes to better forage utilization under grazing. Soil organic carbon (SOC) content in CC decreased with CT, and was maintained with NT only if grain was harvested. In CC systems with harvested forage, SOC decreased even with NT. CPR with NT maintained or increased the original SOC content. The paper concludes with a discussion on the relative sustainability of CC versus CPR with NT. Both are sustainable from the soil quality and productivity standpoints. But compared with CC, CPR is a more economically and climatically buffered system, due to higher diversity. Also, CPR systems are more environmentally sustainable since fuel and agrochemicals usage is reduced approximately 50%.

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 centralwestern, 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, Apatzinga´n and Tepatitla´n) 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 NTand 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. # 2002 Elsevier Science B.V. All rights reserved.

Intensive monocropping of maize is widely practised in densely populated regions of west Africa. A wide range of tillage systems are used for seedbed preparation without the benefits of research information from long-term experiments relating tillage method to soil properties. Soil chemical effects of eight tillage and residue management treatments were studied for 8 years or 16 consecutive maize monoculture crops for a western Nigerian soil with a coarse-textured surface horizon. Treatments established on a newly cleared land were: (1) notill +/- crop residue mulch, (2) notill +/- chiselling in the row zone at 50 cm depth, (3) mouldboard ploughing +/- harrowing, (4) disc ploughing +/- rotovation, (5) notill - residue mulch, (6) mouldboard ploughing at the end of rains or summer ploughing, (7) mouldboard ploughing +/- residue mulch, and (8) mouldboard ploughing and harrowing +/- ridging or ridge till. Soil chemical properties of the 0-5-cm and 5-10-cm depths were measured during the dry season every year beginning with base line characterization soon after land clearing in 1980. Soil pH declined with cultivation duration from 6.6 in 1981 to 5.4 in 1987 for the 0-5-cm depth, and from 6.5 in 1981 to 5.5 in 1987 for the 5-10-cm depth. Mean soil pH for the 0-5-cm depth declined from 6.7 to 5.6 in notill +/- residue mulch, and from 6.7 to 5.4 with mouldboard ploughing. Soil content of Bray P increased with cultivation duration due to application of phosphatic fertilizers. There occurred a significant decrease in soil organic carbon (SOC) and total soil nitrogen (TSN), and an increase in C:N ratio with cultivation duration. Mean SOC content in 1987 of the 0-5-cm depth was 13.9 g kg(-1) for the notill treatment compared with 11.0 g kg(-1) for the plough-based methods. Soil concentration Ca and Mg and total cation exchange capacity (CEC) increased with cultivation duration. Maize grain yield was significantly correlated with SOC, exchangeable Ca2+, and CEC. Continuous cropping decreased soil chemical quality, and the rate of decreases was more with plough-based than notill methods. (C) 1997 Elsevier Science B.V.