Are Partial Nutrient Balances Suitable to Evaluate Nutrient Sustainability of Land use Systems? Results from a Case Study in Central Sulawesi,Indonesia

Nutrient input–output balances are often used as indicators for the sustainability of land use systems. In a case study on plot scale in Central Sulawesi, Indonesia, we measured nutrient input–output balances of natural rainforest and two unfertilized land use systems (maize, and coffee/cacao agroforestry). These are the two major land use systems on converted rainforest sites in this part of Sulawesi. We wanted to test if (a) plant nutrient balances are negative, (b) which pathway is most important for losses of plant nutrients, and (c) if partial plant nutrient balances are suitable to evaluate sustainability of the land use systems. We measured nutrient inputs by precipitation and nutrient outputs by harvest export and leaching. We selected two locations, the first was situated on a fertile Cambisol developed on alluvial sediment soil, and the second on a less fertile Cambisol developed on weathered phyllite substrate. Nutrient losses through leaching were higher on sites with higher soil fertility. Nutrient balances in natural forest on fertile soils were negative for N, Ca, K and Mg. Inputs of P by precipitation and outputs by leaching were below detection limit. On less fertile soils, leaching of N and K in natural forest was lower than inputs by precipitation. As net nutrient losses were highest in agroforestry, followed by maize and natural forest stands, forest conversion into agricultural land will result in increased nutrient losses. Main output pathway of N, P and K was harvest, whereas main output pathway for Ca and Mg was through leaching. The annual losses of nutrients we measured were higher than in comparable studies on nutrient poor soils; however losses were only small fractions of available nutrient stocks. Our results showed negative partial nutrient balances in both agricultural systems. Nutrient balances in this study were more influenced by native soil fertility than by land use. Because we found indirect evidence that some nutrient pathways, which were not measured, may have significantly changed the overall balance (biological N fixation, weathering), we conclude that partial nutrient balances are no good indicators for sustainability of land use systems.     

Crop production,nitrogen recovery and water use efficiency in rice–wheat rotation as affected by non-flooded mulching cultivation (NFMC)

Non-flooded mulching cultivation (NFMC) for lowland rice, as a novel water-saving technique, has been practiced in many areas of China since the 1990s. However, the information on NFMC effects on crop production, nitrogen and water use in rice–wheat rotations is still limited. A field experiment using ¹⁵N-labeled urea was conducted to evaluate the impacts of NFMC on crop yield, fertilizer N recovery and water use efficiency in rice–wheat rotations. Plastic film mulching (PM), and wheat straw and plastic film double mulching (SPM) resulted in the same rice grain yield (7.2 t ha^–1) while wheat straw mulching (SM) and no mulching (NM) led to 5 and 10% yield reduction, compared with rice under traditional flooding (TF). In the rice–wheat rotation, crop productivity in PM, SM or SPM was comparable to that in TF but greater than in NM. Weed growth and its competition with rice for nitrogen were considered the main reason that led to yield decline in NM. Compared with TF, NFMC treatments did not obviously affect fertilizer N recoveries in plant and soil in both rice and wheat seasons. The total fertilizer N recoveries in crop, weed and soil in all treatments were only 39–44% in R–W rotations, suggesting that large N losses occurred following one basal N application for each growing season. Water use efficiency, however, was 56–75% greater in NFMC treatments than in TF treatment in the R–W rotation. The results revealed that NFMC (except NM) can produce comparable rice and wheat yields and obtain similar fertilizer N recovery as TF with much less water consumption.     

Effect of climate change on greenhouse gas emissions from arable crop rotations

The DAISY soil–plant–atmosphere model was used to simulate crop production and soil carbon (C) and nitrogen (N) turnover for three arable crop rotations on a loamy sand in Denmark under varying temperature, rainfall, atmospheric CO₂ concentration and N fertilization. The crop rotations varied in proportion of spring sown crops and use of N catch crops (ryegrass). The effects on CO₂ emissions were estimated from simulated changes in soil C. The effects on N₂O emissions were estimated using the IPCC methodology from simulated amounts of N in crop residues and N leaching. Simulations were carried out using the original and a revised parameterization of the soil C turnover. The use of the revised model parameterization increased the soil C and N turnover in the topsoil under baseline conditions, resulting in an increase in crop N uptake of 11 kg N ha^–1 y^–1 in a crop rotation with winter cereals and a reduction of 16 kg N ha^–1 y^–1 in a crop rotation with spring cereals and catch crops. The effect of increased temperature, rainfall and CO₂ concentration on N flows was of the same magnitude for both model parameterizations. Higher temperature and rainfall increased N leaching in all crop rotations, whereas effects on N in crop residues depended on use of catch crops. The total greenhouse gas (GHG) emission increased with increasing temperature. The increase in total GHG emission was 66–234 kg CO₂-eq ha^–1 y^–1 for a temperature increase of 4°C. Higher rainfall increased total GHG emissions most in the winter cereal dominated rotation. An increase in rainfall of 20% increased total GHG emissions by 11–53 kg CO₂-eq ha^–1 y^–1, and a 50% increase in atmospheric CO₂ concentration decreased emissions by 180–269 kg CO₂-eq ha^–1 y^–1. The total GHG emissions increased considerably with increasing N fertilizer rate for a crop rotation with winter cereals, but remained unchanged for a crop rotation with spring cereals and catch crops. The simulated increase in GHG emissions with global warming can be effectively mitigated by including more spring cereals and catch crops in the rotation.     

Residual phosphorus effects and nitrogen × phosphorus interactions in soybean–maize rotations on a P-deficient Ferralsol

Legume-cereal rotations are an essential component of integrated soil fertility management in low-input cropping systems, but strategies are needed to increase phosphorus (P) fertilizer use efficiency in such systems. These may include preferential targeting of P to one of the crops in the rotation cycle, the use of P-efficient genotypes, and the optimization of the rates of P fertilizer used. A field trial was conducted to evaluate the effects of increasing P fertilizer rates (0, 11, 22 and 44 kg P ha^?1, added as triple super phosphate) applied to three soybean genotypes grown on a P-deficient Ferralsol, on the nitrogen (N) and P nutrition of a subsequent maize crop. In addition, a greenhouse trial was set up to assess N, P and other rotation effects of three soybean genotypes on a subsequent maize crop relative to a maize–maize rotation at high and low P supply. In the field trial, soybean did not respond to increasing P rates, but residual P effects improved maize grain yields by up to 90 %. Ear leaf (field trial) and shoot (pot trial) P concentrations increased by applying N to maize, demonstrating important N × P interactions. The pot trial did not reveal a positive rotation effect of soybean on maize beyond the mere N-benefit, showing that soybean was not able to improve P availability to maize after correcting for the N-effect. No variation in rotation effects on maize among soybean genotypes was observed. Because of the absence of effects of the soybean crop on P availability to maize, opportunities to increase P fertilizer use efficiency in soybean–maize rotations mainly reside in maximizing P uptake by each crop separately and in matching P fertilizer rates with crop demand.     

Can the Synchrony of Nitrogen Supply and Crop Demand be Improved in Legume and Fertilizer-based Agroecosystems? A Review

Asynchrony between nitrogen (N) supply and crop demand is the source of many environmental hazards associated with excess N in the biosphere. In this review, we explore some of the complexity of the synchrony issue in agroecosystems that obtain N via legume rotations or synthetic fertilizers. Studies that have simultaneously compared the fate of both sources of N suggest that in rainfed agricultures, crops recover more N from fertilizer, but a higher proportion of the legume N is retained in the soil and N losses tend not to differ greatly from either source. However, investigations from irrigated cropping systems indicate that legume N is generally less susceptible to loss processes than fertilizers. Such general conclusions need to be qualified by acknowledging that not all comparative studies have used ȁ8best management practices’ when applying the fertilizer or legume residues. When information-intensive management approaches are used, fertilizer-based systems can potentially out-perform the synchrony achieved by legume-based rotations. We suggest that the inclusion of perennials in cropping systems may hold the greatest promise for decreasing the risk of N losses in future farming systems.     

Phosphorus and potassium balance in a corn–soybean rotation under no-till and chiseling

Nutrient use efficiency has become an important issue in agriculture, and crop rotations with deep vigorous rooted cover crops under no till may be an important tool in increasing nutrient conservation in agricultural systems. Ruzigrass (Brachiaria ruziziensis) has a vigorous, deep root system and may be effective in cycling P and K. The balance of P and K in cropping systems with crop rotations using ruzigrass, pearl millet (Pennisetum glaucum) and ruzigrass + castor bean (Ricinus communis), chiseled or not, was calculated down to 0.60 m in the soil profile for 2 years. The cash crops were corn in the first year and soybean in the second year. Crop rotations under no-till increased available P amounts in the soil–plant system from 80 to 100 %, and reduced K losses between 4 and 23 %. The benefits in nutrient balance promoted by crop rotations were higher in the second year and under without chiseling. Plant residues deposited on the soil surface in no-till systems contain considerable nutrient reserve and increase fertilizer use efficiency. However, P release from ruzigrass grown as a sole crop is not synchronized with soybean uptake rate, which may result in decreased yields.     

Does nonlinear dynamic matrix control provide integral control?

Nonlinear dynamic matrix control guarantees integral control if the output horizon is infinite, and may fail to provide integral control if the output horizon is finite, the input weight is nonzero, and dh(u)/du=0 for some u= , where y=h(u) describes the steady-state input–output behavior. Possible modifications to the algorithm to guarantee integral control are discussed.     

Changes in soil available NPK in multiple cropping systems based on short duration sugarcane crops relative to a conventional sugarcane cropping system

Changes in soil available NPK were studied in four intensive crop rotations based on short duration (8 months) sugarcane crops (1. short duration plant cane/1st ratoon/2nd ratoon; 2. short duration plant cane/1st ratoon/finger millet/cotton; 3. finger millet/short duration plant cane/1st ratoon/wheat; and 4. finger millet/maize/short duration plant cane/1st ratoon). These rotations were compared with the conventional duration (12 months) sugarcane crop sequence (one plant + one ratoon) in a cycle of 24 months.Soil available nitrogen (SAN) declined when 100 or 150 kg N ha^–1 was applied in the short duration sugarcane based systems, but was either maintained or improved at a higher N application rates (200 or 250 kg ha^–1). The conventional system showed a sharp decline in SAN of about 14% from its original status at the end of the sequence. Close row spacing (60 cm) of sugarcane improved the soil N level over that in the conventionally spaced rows (90 cm) probably through greater rhizosphere biomass additions.Available P declined sharply from its original level in the soil in sequence 2, the decline being marked after cotton. In all the other short duration based sequences it was maintained. The conventional system also showed reduced soil available P at the end of the sequence. Soil available K declined in all crop sequences.Nitrogen uptake was far less than additions made by fertilizer. The actual soil N balance was much lower than the expected balance thus indicating large losses of N from the soil. Phosphorus removal was also less than the additions made and thus there were improvements in the soil available P status at the end of the crop cycle. In all the sequences, there was a negative potassium balance due to greater removal by the various crops when compared to K additions. However, in the system as a whole there were net gains of K as larger amounts were recovered than had been added.     

Simulating phosphorus responses in annual crops using APSIM: model evaluation on contrasting soil types

Crop simulation models have been used successfully to evaluate many systems and the impact of change on these systems, e.g. for climatic risk and the use of alternative management options, including the use of nitrogen fertilisers. However, for low input systems in tropical and subtropical regions where organic inputs rather than fertilisers are the predominant nutrient management option and other nutrients besides nitrogen (particular phosphorus) constrain crop growth, these models are not up to the task. This paper describes progress towards developing a capability to simulate response to phosphorus (P) within the APSIM (Agricultural Production Systems Simulator) framework. It reports the development of the P routines based on maize crops grown in semi-arid eastern Kenya, and validation in contrasting soils in western Kenya and South-western Colombia to demonstrate the robustness of the routines. The creation of this capability required: (1) a new module (APSIM SoilP) that simulates the dynamics of P in soil and is able to account for effectiveness of alternative fertiliser management (i.e. water-soluble versus rock phosphate sources, placement effects); (2) a link to the modules simulating the dynamics of carbon and nitrogen in soil organic matter, crop residues, etc., in order that the P present in such materials can be accounted for; and (3) modification to crop modules to represent the P uptake process, estimation of the P stress in the crop, and consequent restrictions to the plant growth processes of photosynthesis, leaf expansion, phenology and grain filling. Modelling results show that the P routines in APSIM can be specified to produce output that matches multi-season rotations of different crops, on a contrasting soil type to previous evaluations, with very few changes to the parameterization files. Model performance in predicting the growth of maize and bean crops grown in rotation on an Andisol with different sources and rates of P was good (75–87% of variance could be explained). This is the first published example of extending APSIM P routines to another crop (beans) from maize. Dr R. J. Delve has recently left CIAT and joined Catholic Relief Services, Kenya.     

Fractions of organic carbon in soils under different crop rotations, cover crops and fertilization practices

We investigated the long-term effects (13–48 years) of crop rotations, cover crops and fertilization practices on soil organic carbon fractions. Two long-term experiments conducted on a clay loam soil in southeastern Norway were used. From the crop rotation experiment, two rotations, one with two years grain + four years grass and the second with grain alone (both for 6 years), were selected. Each rotation was divided into moderate fertilizer rate (30–40 kg N ha^–1), normal fertilizer rate (80–120 kg N ha^–1) and farmyard manure (FYM 60 Mg ha^–1 + inorganic N at normal rate). Farmyard manure was applied only once in a 6-year rotation, while NPK was applied to every crop. The cover crop experiment with principal cereal crops consisted of three treatments: no cover, rye grass and clover as cover crops. Each cover crop was fertilized with 0 and 120 kg ha^–1 N rates. Soil samples from both experiments were taken from 0–10 cm and 10–25 cm depths in the autumn of 2001. The classical extraction procedure with alkali and acid solution was used to separate humic acid (HA), fulvic acid (FA) and humin fractions, while H₂O₂ was used to separate black carbon (BC) from the humin fraction. The rotation of grain + grass showed a significantly higher soil organic carbon (SOC) compared with grain alone at both depths. Farmyard manure application resulted in significantly higher SOC than that of mineral fertilizer only. However, cover crops and N rates did not affect SOC significantly. Organic carbon content of FA, HA and humin fractions accounted for about 29%, 25% and 44% of SOC, respectively. The rotation of grain+grass gave a higher C content in HA and humin fractions, and a lower C in the FA fraction as compared with the rotation with grain alone. Farmyard manure increased HA and humin fractions more than did chemical fertilizers. Clover cover crop increased the C proportion of humin more than rye grass and no cover crop. No significant differences in C contents of FA, HA and humin fractions were observed between N rates. Effects of cover crop and N rates as well as fertilization with NPK on black carbon (BC) content were significant only at 10–25 cm depths. Farmyard manure increased the BC fraction compared with chemical fertilizers. Clover crop also enhanced the accumulation of the BC fraction. Application of 120 kg N ha^–1 resulted in a significant increase of the BC fraction.     

Gross nitrogen mineralization in pulse-crop rotations on the Northern Great Plains

Pulse crops represent an ever-increasing proportion of cropping systems in the Northern Great Plains. Previous studies have noted apparent benefits associated with pulse crop production that extend beyond the reduced need for N fertilizer in the year of production; these benefits have been attributed to the quality of pulse residues and their effects on N dynamics in subsequent years. This study used isotope dilution techniques to quantify the N-cycling effects of pulse crops in the rotation. Gross N mineralization was measured over three growing seasons at two Agriculture and Agri-Food Canada research sites in Saskatchewan, Canada: Scott (four rotations; one with pulse crop) and Swift Current (three rotations; one with pulse crop). Gross nitrification and the relative contribution of nitrification vs. denitrification to N₂O emissions were also measured. Across all dates and rotations, the average gross mineralization rate at Scott was 2.0 ± 4.0 mg NH₄ ⁺-N kg^?1 soil d^?1 and at Swift Current was 1.4 ± 3.9 mg NH₄ ⁺-N kg^?1 soil d^?1. At both sites, rates were highly variable across the growing season, but tended to be higher at anthesis than either pre-seeding or post-harvest. The only significant difference among rotations was at Swift Current, where the fertilized continuous wheat rotation had the highest gross mineralization rates (rotation average: 2.3 mg NH₄ ⁺-N kg^?1 soil d^?1). The lack of difference among most rotations was particularly notable given the differences in residue quantity among the crops. Ultimately, the lower quantity of residues produced by pulse crops appears to be offset by their higher quality.     

Alternatives for nitrogen nutrition of crops in tropical agriculture

The development of sustainable agricultural systems for the tropics requires among other technologies, alternatives for nitrogen fertilizers which are often limited in availability for financial reasons and also represent a major source of groundwater and air pollution. There are many new alternatives for the development of agricultural systems which make use of biological processes in soil. Biological nitrogen fixation (BNF), that is, the biological conversion of atmospheric dinitrogen into mineral N, is the most important alternative among them. Examples are given of the impact of various technologies used in Brazil. Soybean, introduced into the country 30 years ago, is now the second most important export crop, reaching 24 million tons annually with no N fertilizer application. Consequently, Brazil today is the country in the world which uses the lowest amounts of nitrogen fertilizers in relation to phosphate. Alternatives for crop rotations and pastures are also discussed. Possibilities of expanding BNF to cereals and other non-legume crops are gaining new credibility due to the identification of endophytic associations with diazotropic bacteria. The definite proof of substantial BNF in sugar cane with N balance and¹⁵N methods in certain genotypes selected under low N fertilizer applications opens up new alternatives for sustainable agriculture and will be the key to viable bio-fuel programmes.     

Effects of input level and crop diversity on soil nitrate-N,extractable P,aggregation, organic C and N,and nutrient balance in the Canadian Prairie

A field experiment was conducted from 1995 to 2006 on a Dark Brown Chernozem (Typic Boroll) loam soil at Scott, Saskatchewan, Canada to determine the influence of input level and crop diversity on accumulation and distribution of nitrate-N and extractable P in the soil profile, and soil pH, dry aggregation, organic C and N, and nutrient balance sheets in the second 6-year rotation cycle (2001–2006). Treatments were combinations of three input levels (organic input under conventional tillage—ORG; reduced input under no-till—RED; and high input under conventional tillage—HIGH), three crop diversities (fallow-based rotations with low crop diversity—LOW; diversified rotations using annual cereal, oilseed and pulse grain crops—DAG; and diversified rotations using annual grain and perennial forage crops—DAP), and six crop phases including green manure (GM), chem-fallow or tilled-fallow (F). Amount of nitrate-N in 0-240 cm soil was usually highest under the HIGH input-LOW crop diversity treatment and lowest under the ORG input-DAP crop diversity treatment. The distribution of nitrate-N in various soil depths suggested downward movement of nitrate-N up to 240 cm depth, especially with LOW crop diversity compared to DAP crop diversity, and with HIGH input. In some years, the ORG input systems had higher nitrate-N than the RED or HIGH input systems, which was attributed to low extractable P in soil for optimum crop growth and reduced nutrient uptake with ORG input management. Extractable P in soil was higher by a small margin for HIGH or RED input relative to ORG input in the 0–15 cm layer, suggesting little downward movement of P. Crop diversity did not affect extractable soil P due to the low baseline levels of P in this soil. The proportion of fine dry aggregates (<1.3 mm, erodible fraction) in 0–5 cm soil was highest with LOW crop diversity-HIGH input system, and lowest with DAG diversity-RED input system. The opposite was true for large aggregates (>12.7 mm). Wet aggregate stability was higher for RED input compared to ORG and HIGH input, which was attributed to the increase in the concentration of organic C in aggregates in the RED input system. Amount of light fraction organic matter (LFOM), light fraction organic C (LFOC) and light fraction organic N (LFON) in 0–15 cm soil was higher for RED input compared to ORG and HIGH inputs, and higher for DAG and DAP crop diversities than for LOW crop diversity. Soil N and P were usually deficient under ORG input management, but large amounts of N and P were unaccounted for, or in surplus, under RED and HIGH inputs, despite a marked increase in plant N and P uptake and crop yield compared to ORG input. Overall, our findings suggest that soil quality can be improved and nutrient accumulation in the soil profile can be minimized by increasing cropping frequency, reducing/eliminating tillage, and using appropriate combinations of fertilizer input and diversified cropping.     

ICBM regional model for estimations of dynamics of agricultural soil carbon pools

Swedish arable land covers 3 Mha and its topsoil contains about 300 Mton C. The mineral soils seem to be close to steady-state, but the organic soils (about 10% of total arable land) have been estimated to lose ca. 1 Mton/year. We have devised a conceptual model (ICBMregion), using national agricultural crop yield/manuring statistics and allometric functions to calculate annual C input to the soil together with a five-parameter soil carbon model (ICBMr), calibrated using long-term field data. In Sweden, annual yield statistics are reported for different crops, for each of eight agricultural regions. Present topsoil carbon content and regional distribution of soil types have recently been measured. We use daily weather station data for each region together with crop type (bulked from individual crop data) and soil type to calculate an annual soil climate parameter for each crop/soil type permutation in each region. We use 14 soil types and 9 crop types, which gives 126 parameter sets for each year and region, each representing a fraction of the region's area. For each year, region, crop and soil type, ICBMregion calculates the change in young and old soil carbon per hectare, and sums up the changes to, e.g., national changes. With eight regions, we will have 1008 parameter sets per year, which easily can be handled, and what-if scenarios as well as comparisons between benchmark years are readily made. We will use the model to compare the soil C pools between the IPCC benchmark year 1990 and the present. In principle, we use inverse modelling from the sampled, recent soil C pools to estimate those in 1990. In the calculations, soil climate and yield for each year from 1990 onwards are taken into account. Then we can project soil C balances into the future under different scenarios, e.g., business as usual, land use change or changes in agricultural crops or cultivation practices. Projections of regional climate change are also available, so we can quite easily make projections of soil C dynamics under, e.g., different climate scenarios. We can follow the dynamic effects of carbon sequestration efforts – and estimate their efficiency. The approach is conceptually simple, fairly complete, and can easily be adapted to different needs and availability of data. However, perhaps the greatest advantage is that the results from this comprehensive approach used for, e.g., a 10-year period, can be condensed into a very simple spreadsheet model for calculating effects of management/land use changes on C stocks in agricultural soils.     

The role of legume fallows in intensified upland rice-based systems of West Africa

Traditional upland rice-based cropping systems in West Africa rely on periods of fallow to restore soil fertility and prevent the build-up of insect pests and weeds. Demographic growth and increased demand for land is forcing many farmers to intensify their rice production systems. Declining fallow length and increasing number of crops before leaving the land to extended fallow result in a significant yield reduction. Promising cropping system alternatives include the use of site specific, weed-suppressing, multi-purpose cover legumes as short duration fallows. Constraints to rice production related to intensification were determined in 209 farmers' fields in four agro-ecological zones during 1994 and 1995. Nitrogen accumulation and weed suppression were evaluated in 54 legume accessions, grown for six months during the dry season, under a range of hydrological and soil conditions in 1994/95. Their effect on the yield of upland rice was determined in 1995. To increase benefits from improved fallow technology, the timing of legume establishment in relation to rice and the effect on crop and weed growth of removing, burning, mulching, or incorporating fallow residues prior to the rice crop were determined. Intensified land use resulted in a significant plot-level yield reduction that was highest in the derived savanna and the bimodal forest zones where it was associated with a doubling of the weed biomass in rice and a significant reduction in soil N supply. Legume fallows appear to offer the potential to sustain rice yields under intensified cropping. Legume biomass was in most instances significantly greater than in the weedy fallow control and several legume species suppressed weed growth. Nitrogen accumulation by legumes varied between 1–200 kg N ha-1 with 30–90% Ndfa. Rice grain yield following legume fallows increased by an average of 0.2 mg ha-1 or 29% above the weedy fallow control. Relay establishment substantially increased legume biomass. However, seeding of the legume at 28 days or earlier significantly reduced grain yield due to interspecific competition. Incorporating or mulching of fallow residues provided no significant yield advantage as compared to burning. Absolute effects varied as a function of site, legume species, and management practice.     

Carbon sequestration in soil aggregates under different crop rotations and nitrogen fertilization in an inceptisol in southeastern Norway

Effects of crop rotation and fertilization (nitrogen and manure) on concentrations of soil organic carbon (SOC) and total soil nitrogen (TSN) in bulk soil and in soil aggregates were investigated in a long-term field experiment established in 1953 at Ås, Norway. The effect of these management practices on SOC sequestration was estimated. The experiment had three six-course rotations: (I) continuous spring grain, (II) spring grain for 3 years followed by root crops for 3 years, and (III) spring grain for 2 years followed by meadow for 4 years. Three fertilizer treatments compared were: (A) 30–40 kg N ha^–1; (B) 80–120 kg N ha^–1; and (C) a combination of B and 60 Mg farmyard manure (FYM) ha^–1. All plots received a basal rate of PK fertilizer. Soil samples from these treatments were collected in autumn 2001 and analyzed for aggregate size, SOC and TSN concentrations. There were significant increases in 0.6–2 mm and < 0.6 mm aggregate size fractions, and reduction in the 6–20 mm and the > 20 mm sizes for rotation III only. There were also significant differences among rotations with regard to water stable aggregation. The order of increase in stability was II < I < III. Fertilizer treatment had no effect on aggregation or aggregate size distribution, but there was a slight tendency of increased stability with the application of FYM. Aggregate stability increased with increasing concentration of SOC (r2 = 0.53). The SOC and TSN concentrations in bulk soil were significantly higher in rotation III than in rotations II and I. Application of FYM increased SOC and TSN concentrations significantly in the 0–10 cm soil depth, but there were few significant differences between fertility treatments A and B. There was a trend of increase in concentration of SOC and TSN with decreasing aggregate size, but significant differences in these parameters in different aggregate size fractions were found only in few cases. The SOC and TSN concentrations were higher in >0.25 mm than in < 0.25 mm aggregates. The SOC sequestration rate was 77–167 kg SOC ha^–1 yr^–1 by increasing the N rate and 40–162 kg SOC ha^–1 yr^–1 by applying FYM. The SOC sequestration rate by judicious use of inorganic fertilizer was the greatest in the grain–meadow rotation, while that by application of FYM was the greatest in the all grain rotation.     

Nitrogen management in organic farming: comparison of crop rotation residual effects on yields,N leaching and soil conditions

After 3 years of different crop rotations in an organic farming experiment on a sandy soil in northwest Germany, spring triticale was cultivated on all plots in the fourth year to investigate residual effects on yield, nitrogen (N) leaching and nutrient status in the soil. Previous crop rotations differed in the way N was supplied, either by farmyard manure (FYM, 100 and 200 kg N ha⁻¹ year⁻¹) or by arable legumes like grass-red clover and field beans, or as a control with no N. Other crops in the rotations were maize, winter triticale and spring barley. Additional plots had a 3-year grass-clover ley, that was ploughed-in for spring triticale in the fourth year. Yields of spring triticale were moderate and largest for ploughed-in grassland leys and grass-red clover and plots that had previously received farmyard manure. The former crop rotation, including grassland break-up, had a significant effect on most yield and environmental parameters like residual soil mineral nitrogen (SMN) and N leaching and on the level of available K in the soil. The single crop harvested in the year before spring triticale had a significant effect on yield parameters of spring triticale, less so on SMN and N leaching in the fourth year and no effect on available nutrients (P, K, Mg) and pH in the soil. We conclude that the effects of arable legumes were rather short lived while ploughing of 3-year grassland leys had a profound influence on mineralization processes and subsequently on yield and N losses.     

Nitrogen leaching and crop availability in manured catch crop systems in Sweden

Results are presented from five years (1990–1995) of a field leaching experiment on a sandy soil in south-west Sweden. The aim was to study N leaching, change in soil organic N and N mineralization in cropping systems with continuous use of liquid manure (two application rates) and catch crops. N leaching from drains, N uptake in crops and mineral N in the soil were measured. Simulation models were used to calculate the N budget and N mineralization in the soil and to make predictions of improved fertilization strategies in relation to manure applications and changing the time for incorporation of catch crops. In treatments without catch crops, a normal and a double application of manure increased average N leaching by 15 and 34%, respectively, compared to treatment with commercial fertilizer. Catch crops reduced N leaching by, on average, 60% in treatments with a normal application of manure and commercial fertilizer, but only by 35% in the treatment with double the normal application rate of manure. Incorporation of catch crops in spring increased simulated net N mineralization during the crop vegetation period, and also during early autumn. In conclusion, manured systems resulted in larger N leaching than those receiving commercial fertilizer, mainly due to larger applications of mineral N in spring. More careful adaptation of commercial N fertilization with respect to the amounts of NH₄-N applied with manure could, according to the simulations, reduce N leaching. Under-sown ryegrass catch crops effectively reduced N leaching in manured systems. Incorporating catch crop residues in late autumn instead of spring might be preferable with respect to N availability in the soil for the next crop, and would not increase N leaching.     

The effect of nitrogen source and crop rotation on the growth and yield of processing tomatoes

Four crop rotation and management systems were studied in 1994 and 1995 in relation to growth and yield of irrigated processing tomatoes (Lycopersicon esculentum Mill.). The four treatments were three four-year rotation systems [conventional (conv-4), low input and organic] and a two-year rotation system [conventional (conv-2)]. The four-year rotation was tomato-safflower-corn-wheat(or oats+vetch)/beans, and the two-year rotation was tomato-wheat. Purple vetch (Vicia sativa L.) was grown as a green manure cover crop preceeding tomatoes in the low input and organic systems. Nitrogen was supplied as fertilizer in the conventional systems, as vetch green manure plus fertilizer in the low input system and as vetch green manure plus turkey manure in the organic system. Tomato cv. Brigade was direct-seeded in the conventional systems and transplanted to the field in the low input and organic systems. In both years the winter cover crop was composed of a mixture of vetch and volunteer oats with N contents of 2.2% in 1994 and 2.7% (low input) or 1.8% (organic) in 1995. In 1994 yields were higher in conventionally grown tomatoes because a virus in the nursery infected the transplants used in the low input and organic systems. In 1995 tomatoes grown with the low input and conv-4 systems had similar yields, which were higher than those of tomatoes grown with the conv-2 and organic systems. N uptake by the crop was greater than 200 kg N ha^–1 for high yield (> 75 t ha^–1) and uptake rates of 3 to 6 kg N ha^–1 day^–1 during the period of maximum uptake were observed. The lower yield with the organic system in 1995 was caused by a N deficiency. The main effect of the N deficiency was a reduced leaf area index and not a reduction of net assimilation rate (NAR) or radiation use efficiency (RUE). Nitrogen deficiency was related to low concentration of inorganic N in the soil and slow release of N from the cover crop + manure. A high proportion of N from the green manure but only a low proportion of N from the manure was mineralized during the crop season. In the conventional systems, the estimated mineralized N from the soil organic matter during the crop season was around 85 kg ha^–1. A hyperbolic relationship between N content and total dry weight of aboveground biomass was observed in procesing tomatoes with adequate N nutrition. Lower yields with the conv-2 than with the conv-4 system were due to higher incidence of diseases in the two year rotation which reduced the NAR and the RUE. Residual N in the soil in Oct. (two months after the incorporation of crop residues) ranged between 90 and 170 kg N ha^–1 in the 0–90 cm profile.Department of Vegetable Crops.     

Improved fallow: growth and nitrogen accumulation of five native tree species in Brazil

Nitrogen (N) is the most important yield-limiting factor in agricultural systems, however, N application can lead to emissions and environmental problems such as global warming (N₂O) and groundwater contamination (NO₃ ^?). This study analyses the N balance, nitrogen-use efficiency, and N loss potential of conventional farming systems (arable farming, improved arable farming, and agroforestry) and organic farming systems (mixed farming, arable farming, and agroforestry) based on long-term field experiments in southern Germany. The effects of the conversion of farm structure and N management are identified. The conventional farming systems in this study were high N-input and high N-output systems. The conventional arable farming system had the lowest nitrogen-use efficiency and the highest N surplus. An optimised N management and the use of high-yielding crop varieties improved its nitrogen-use efficiency. The establishment of conventional agroforestry resulted in the reduction of N input, N output and N surplus, while maintaining high yields. The organic mixed farming system is characterised by a relatively high N input and N output, the accumulation of soil organic nitrogen, the highest nitrogen-use efficiency, and the lowest N surplus of all analysed systems. These good results can be attributed to the intensive farm N cycle between soil–plant–animal. The shift from organic mixed farming to organic arable farming system extensified the N cycle, reduced N input, crop yield and N output. The change from organic arable farming to organic agroforestry reduced the N input, increased the biomass yield, and remained the N surplus within an optimal range.