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Field and greenhouse pot experiments were conducted to evaluate the potential to use intercropping as an alternative method to increase glucosinolates in Brassicas by manipulating nitrogen (N) and sulfur (S) balance by intercropping with lettuce (Lactuca sativa L. var. capitata). In both experiments, four combinations of N and S fertilization were used. In the field experiment no effect of intercropping on the total glucosinolate concentration was found as the growing lettuce was strongly inhibited by the presence of broccoli (Brassica oleracea L. var. italic). In contrast to this, in the pot experiment both total and individual glucosinolate concentrations in red leaf mustard (Brassica juncea L.) increased by intercropping. Fertilization treatments influenced glucosinolate concentrations in both experiments, and an interaction between N and S fertilization was noticed.

The hypothesis that delayed addition of nutrient rich material to compost would influence the mineralisation pattern was investigated by studying N turnover in compost based on wheat straw and clover-grass hay. After 712 weeks of composting almost twice as much N was mineralised when the addition of some of the N-rich clover-grass hay was postponed, suggesting that this influenced the microbial succession. The delayed addition resulted in a second temperature peak and a decline in the pH. Despite the altered conditions no significant effect was observed on the weight loss or loss of C and N. In conclusion, compost processes can in a simple way be affected by delayed substrate application leading to a higher nutrient availability without altering other parameters significantly.

Determining genotypic responses to soil fertility may assist selection of cultivars that can be adapted to varied soil fertility regimes, and such selection under field conditions is still limited. A two-year field experiment was conducted in long-term field trials to investigate wheat genotype effects on early growth, yield and nutrient accumulation as affected by varied long-term soil fertility managements and nitrogen (N) fertilization. Results show that the early growth, grain yield and nutrient accumulation of spring wheat plants were strongly affected by soil fertility managements and genotypes. Early shoot and root biomass of singly grown plants and leaf canopy growth under standard growth density was associated with subsequent grain yield of plants under standard growth density across the gradient in soil fertility levels. Taifun and Thasos had stable higher yield and N and phosphorus (P) uptake across varied soil fertility regimes compared with other genotypes. Økilde, however, increased yield by 8–34% and N and P accumulation by 1–22% only when grown in the high organic manure treatment compared with other genotypes, indicating that it is more adapted to high organic fertility regimes. Therefore, the different responses and adaptations of genotypes to soil fertility regimes should be included during selection of cultivars. [ABSTRACT FROM AUTHOR]

We present a 2-D model for simulation of root density and plant nitrogen (N) uptake for crops grown in agricultural systems, based on a modification of the root density equation originally proposed by Gerwitz and Page in J Appl Ecol 11:773–781, (). A root system form parameter was introduced to describe the distribution of root length vertically and horizontally in the soil profile. The form parameter can vary from 0 where root density is evenly distributed through the soil profile, to 8 where practically all roots are found near the surface. The root model has other components describing root features, such as specific root length and plant N uptake kinetics. The same approach is used to distribute root length horizontally, allowing simulation of root growth and plant N uptake in row crops. The rooting depth penetration rate and depth distribution of root density were found to be the most important parameters controlling crop N uptake from deeper soil layers. The validity of the root distribution model was tested with field data for white cabbage, red beet, and leek. The model was able to simulate very different root distributions, but it was not able to simulate increasing root density with depth as seen in the experimental results for white cabbage. The model was able to simulate N depletion in different soil layers in two field studies. One included vegetable crops with very different rooting depths and the other compared effects of spring wheat and winter wheat. In both experiments variation in spring soil N availability and depth distribution was varied by the use of cover crops. This shows the model sensitivity to the form parameter value and the ability of the model to reproduce N depletion in soil layers. This work shows that the relatively simple root model developed, driven by degree days and simulated crop growth, can be used to simulate crop soil N uptake and depletion appropriately in low N input crop production systems, with a requirement of few measured parameters. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents simulations of the soil–plant–atmosphere model DAISY based on an organic crop rotation with incorporation of different catch crops following pea as a leguminous cash crop. Special emphasis was placed on the simulation of nitrogen (N)-mineralisation/immobilisation and of soil microbial biomass N. The DAISY model was able to simulate soil mineral N and soil microbial biomass N after soil incorporation of catch crop plant residues to some extent only. Several processes need further attention and should be integrated into the DAISY model: (1) soil tillage induced mobilisation of organic material including considerable amounts of organic N; (2) winter killing of sensitive plant species and varieties; (3) decomposition of plant residues at the soil surface; (4) decomposition of easily decomposable plant residues at low temperatures, both with respect to the temperature modifier function and to the linkage of C and N turnover; (5) furthermore, reliable criteria for the subdivision of green plant residues into an easily decomposable pool and a more recalcitrant pool have to be developed. [Copyright &y& Elsevier]

Investigates the use of catch crops and green manure as biological tools in nitrogen management in temperate zones. Nitrogen effects of catch crops in agriculture; Growth and uptake potential of nitrogen; Relationship between soil depletion and nitrate leaching; Effect of catch crop on nitrogen supply for subsequent crops.

We examined the decomposition of Medicago lupulina, Melilotus alba and Poa pratensis at 3, 9, and 25 deg. C during 4 weeks. There was a strong temperature effect on the rate of CO2 evolution, and thus the extent of energy exhaustion from the added substrates. However, there was no concomitant retardation of N mineralisation at lowtemperatures. In the analysis of variance of mineralized N the residue type gave a 10 times larger contribution to the regression than the temperature (T), whereas for CO2 evolution residue type and temperature were equally important contributors. This indicates that although the temperature has a statistically significant effect on N-mineralisation it is substantially less than compared with the effect on carbon mineralisation in the materials examined. The retardation of carbon mineralisation was least strong in Melilotus alba that had a relatively low cellulose content, and a higher content of low molecular compounds. Though more research will be necessary to consolidate and explain this phenomena, it is likely that an important factor is a decrease in the bioavailability of C-rich polymers at low temperatures, and thus a preferential utilization of N-rich low molecularsubstances. Nitrification was not effectively deterred at 3 deg. C.Thus, in terms of management, it is pertinent to reconsider the timing of green manure and catch crop incorporation in cool temperate climate regions, since the rapid release of nitrogen, coupled with the relatively undeterred nitrification may result in a high N leaching risk by early incorporation, but a low risk for N immobilization at late incorporation, if N rich residues are used. [ABSTRACT FROM AUTHOR]

Models play an important role in optimizing fertilizer use in agriculture to maintain sustainable crop production and to minimize the risk to the environment. In this study, we present a new Simulation Model for Crop Response to Nitrogen fertilizer (SMCR_N). The SMCR_N model, based on the recently developed model EU-Rotate_N for the N-economies of a wide range of crops and cropping systems, includes new modules for the estimation of N in the roots and an associated treatment of the recovery of soil mineral N by crops, for the reduction of growth rates by excessive fertilizer-N, and for the N mineralization from soil organic matter. The validity of the model was tested against the results from 32 multi-level fertilizer experiments on 16 different crop species. For this exercise none of the coefficients or parameters in the model was adjusted to improve the agreement between measurement and simulation. Over the practical range of fertilizer-N levels model predictions were, with few exceptions, in good agreement with measurements of crop dry weight (excluding fibrous roots) and its %N. The model considered that the entire reduction of soil inorganic N during growth was due to the sum of nitrate leaching, retention of N in fibrous roots and N uptake by the rest of the plant. The good agreement between the measured and simulated uptakes suggests that in this arable soil, losses of N from other soil processes were small. At high levels of fertilizer-N yields were dominated by the negative osmotic effect of fertilizer-N and model predictions for some crops were poor. However, the predictions were significantly improved by using a different value for the coefficient defining the osmotic effect for saline sensitive crops. The developed model SMCR_N uses generally readily available inputs, and is more mechanistic than most agronomic models and thus has the potential to be used as a tool for optimizing fertilizer practice. [Copyright &y& Elsevier]