Search

Background: In a long‐term rotation experiment (2016–2022) with different nitrogen (N) fertilizer levels in subtropical South‐India, crop yields of low N plots were unexpectedly high. We therefore hypothesized that in the absence of mineral N application, these yields are largely due to N inputs by N2 fixation in the component crops. To assess the diazotrophic N2‐fixation of lablab (Lablab purpureus L. Sweet) and possible associative N2‐fixation of finger millet (Eleusine coracana L. Gaertn), a controlled experiment was conducted during the 2021 monsoon season within the above‐mentioned long‐term field study. Two approaches were used to estimate the quantity of N derived from the atmosphere (Ndfa): the dilution method using a 15N‐labeled fertilizer and the natural abundance method. Method: For the 15N dilution method irrigated maize (Zea maize L.), finger millet and lablab were labeled with two split applications of 10% 15N fertilizer (50:50 15N‐urea and 15N‐ammonium sulfate) amounting to a total of 15 kg N ha−1. Maize was selected as the non‐fixing reference plant to estimate diazotrophic N2‐fixation. The entire aboveground biomass of the labeled plants was harvested at maturity and analyzed for total DM, N concentration, and the 15N isotope ratio. Results: N2 fixation efficiency for lablab was 52%–69% depending on the calculation method, corresponding to 40–53 kg N ha−1. For finger millet, the natural abundance method resulted in an estimated N2‐fixation of 5 kg N ha−1, which was suggested by the results of the dilution method whereby the reference plant maize was only poorly labeled. Conclusion: Labeling of maize might have been diluted due to unexpected associative N2‐fixation or N‐uptake from unlabeled deep soil N pools. The data underline the importance of symbiotic N2‐fixation in crop rotation systems of South‐India. [ABSTRACT FROM AUTHOR]

Background: In practical farming, there is often a need for short‐term availability of information on the soil nutrient status. Aims: To develop a new express method for the extraction of major plant‐available nutrients and measurement of soil nutrients. In future, this method shall serve for in‐field measurements of soil samples with an ion‐sensitive field‐effect transistor (ISFET). Methods: Various extraction conditions such as type of extractant, soil‐to‐solution ratio, time, and intensity were investigated on a broad selection of dried soil samples in the laboratory. Based on 83 field‐moist soil samples with varying clay contents, these conditions were compared to standard laboratory methods. Results: With increasing extraction time, the nutrient concentrations increased. When the soil‐to‐solution ratio was reduced, a greater share of nutrients was extracted, independent of soil type. H2O and 0.01 M CaCl2 and standard calcium‐acetate‐lactate (CAL) solution proved to be too weak in the short period to reach the ISFET sensor measurement range. Higher concentrated CAL solutions performed much better. Finally, a 5‐min CaCl2 extraction followed by the removal of an aliquot for the determination of soil pH and NO3− was found to be effective. The remaining solution was then mixed with 0.20 M CAL solution for the analysis of H2PO4− and K+ at 10 min of extra extraction time. This extraction method showed very good correlations with the values based on the German laboratory reference methods for pH (R2 = 0.91) and for nitrate (R2 = 0.95). For phosphorus and potassium, we obtained an R2 of 0.70 and 0.81, respectively, for all soils. When soils were grouped according to clay content higher correlations were found. Conclusions: A new express method based on a wet‐chemical approach with a soil preparation procedure was successfully developed and validated. This seems to be a valuable basis for future in‐field measurements via ISFET. [ABSTRACT FROM AUTHOR]

Background: Pig slurries account for a large proportion of the organic manure available worldwide. Because of the large range of slurry compositions, farmers need fast and accurate alternatives to laboratory methods to assess nutrient concentrations in these farm‐based fertilizers. In this way, nutrient emissions into the environment can be reduced and targeted nutrition of crops can be implemented, while mineral fertilizers can be saved. Aim: The objective was to evaluate whether it is possible to rapidly determine ammonium and potassium concentrations in pig slurries on‐farm using ion‐selective electrodes (ISE) and to compare the measurement with established methods. Methods: A total of 391 pig slurry samples were collected from farms in north‐west Germany, and ammonium and potassium concentrations were analyzed in the laboratory. Then the composition of pig slurries was measured with ISE, the Quantofix‐N‐Volumeter (QV) and an electrical conductivity (EC) meter and regression models were used to evaluate the on‐farm quick tests. Results: For the 391 pig slurries studied, regressions with an R2 of 0.92 for ammonium and 0.91 for potassium were achieved for concentrations measured with the ISE in comparison with laboratory analyzes. The model fits for the electrodes were significantly higher than those based on the EC for ammonium and potassium, and it was equivalent to the QV method for the assessment of the ammonium concentration. Conclusion: Due to the simple and rapid measurement, ISE offer high potential for on‐farm quantification of ammonium and potassium concentrations in pig slurries. [ABSTRACT FROM AUTHOR]

Background: Optimum potassium (K) nutrition is essential for high sugar yield and quality of beet crops. Aims: We quantified the effect of potassium deficiency on sugar beet dry matter and sugar yield formation during the growing season. Methods: Sugar beets were grown on low, medium, and high soil K concentrations in a long‐term K fertilizer field experiment on a silt loam alluvial soil. Plants were harvested at four time points during the growing season, including the final harvest. At each harvest, the dry matter yield and K concentration of leaves and beets (when applicable) were recorded, allowing us to study their growth rates in different growth phases. At the final harvest, sugar concentration and internal beet quality were measured. Results: Low soil K concentrations resulted in an approximately 10% lower sugar yield compared to high soil K supply. Interestingly, retarded growth of low K plants already occurred during the germination phase and in the first weeks thereafter, whereas later on, growth rates were similar. Higher soil K levels led to an increased K uptake rate and thus a higher final total K uptake. High K plants showed rapid youth growth and reached their maximum growth rates earlier than plants grown under low K conditions. The initial differentiation between the low and high K treatments persisted because the plants subsequently grew at similar growth rates at both low and high soil K supplies. Conclusion: The early growth reduction in the low K treatment was probably caused by the low amount of K stored in sugar beet seeds in combination with low K availability in the soil. It is concluded that under overall low soil K conditions, adequate amounts of K fertilizer should be applied to meet the demand of sugar beet seedlings for maximum growth and final sugar yield. Banded K fertilizer application next to the plant rows is supposed to be efficient for this purpose. [ABSTRACT FROM AUTHOR]

Under the hot and moist conditions of irrigated agriculture in the arid subtropics, turnover of organic matter is high, which can lead to considerable carbon (C) and nitrogen (N) losses. Therefore, sustainable use of these soils requires regular manure application at high rates. To investigate the contribution of consecutive manure applications to an arid sandy soil to various soil N pools, goat manure was isotopically labeled by feeding 15N‐enriched Rhodes grass hay and applied to the soil during a two‐year field experiment. In the first year, soils received 15N‐labeled manure to distinguish between soil‐derived and manure‐derived N. In the second year, these plots were split for the application of either 15N‐labeled or unlabeled manure to discriminate N derived from previous (first year) and recent (second year) manure application. Soil samples (of control and 15N‐manured soil) were collected at the end of the first and the second year, and incubated in two laboratory experiments with labeled or unlabeled manure. At the beginning of Experiment 1, 7% of total N, 11% of K2SO4 extractable N, and 16% of microbial biomass N were derived from previously field‐applied manure. While the application of manure during incubation increased microbial biomass N by 225% and 410% in the control soil and the previously field‐manured soil, respectively, N2O emissions were more affected on the control soil, releasing considerable amounts of the soil N‐pool (80% of total emissions). In Experiment 2, 4% of total N, 7% of K2SO4 extractable N, and 7% of microbial biomass N derived from previously applied manure, and 4%, 8%, and 3% from recently applied manure, respectively. Microbial biomass N and N2O‐N derived from manure declined with time after manure application, whereas in Experiment 1 this tendency was only observed for microbial biomass N. [ABSTRACT FROM AUTHOR]

Abstract: Nitrogen (N) surpluses from fertilizer application can cause major environmental harm including pollution of surface water, groundwater, and air. To assess such negative externalities, N balances are a complex but useful tool to predict surpluses and to measure effects of nutrient optimization strategies in agriculture. The Yaqui Valley in north‐western Mexico is representative for thousands of square kilometres of intensive, irrigated wheat production under arid conditions worldwide and has been targeted for conservation agriculture in recent years. For these cropping systems, detailed N balances are scarce and often incomplete. To help fill this knowledge gap, data from a long‐term experiment were collected in 2013/14 on a Vertisol to examine the impact of three tillage‐straw management practices (CTB: conventionally tilled beds; PB‐straw: permanent raised beds with residue retention; PB‐burn: permanent raised beds with residue burning) on N dynamics. Tillage had significant effects on soil NO3‐N, NH4‐N, and total N contents across the cropping period. Soil total N content was at all sampling depths lowest in CTB. Soil NO3‐N in the 0–90 cm profile was highest in PB‐burn over the cropping period and ranged from 77 kg ha−1 in the bed before pre‐planting fertilizer application up to 269 kg ha−1 in the furrow after the second fertilizer application. Annual simple N balances were +59 kg N ha−1 in CTB, +39 kg N ha–1 in PB‐straw, and +46 kg N ha−1 in PB‐burn. Residual mineral soil N was significantly affected by tillage‐straw management and lowest for PB‐straw (+205 kg N ha−1) and highest for CTB, and for PB‐burn (+283 kg N ha−1 each) in the 0–90 cm soil profile. Soil NO3‐N moved out of the effective wheat root zone, as indicated by the high residual NO3‐N content at 30–90 cm depth, which is an important pathway of N leaching. Quantifiable N losses through leaching and volatilization averaged 100 kg N ha−1. Our findings suggest that there is potential for substantial reductions in N inputs in all tillage‐straw systems to decrease N losses and to reduce mineral residual soil N, but care should be taken to avoid reducing grain protein content, which in PB straw was already below the quality standard. A knowledge transfer of the European “Nmin” concept is advisable in this region to regulate N fertilizer over‐application. [ABSTRACT FROM AUTHOR]

Enhancing crop water-use efficiency (WUE) is a major research objective in water-scarce agroecosystems. Potassium (K) enhances WUE and plays a crucial role in mitigating plant stress. Here, effects of K supply and PEG-induced water deficit on WUE of spring wheat ( Triticum aestivum L. var. Sonett), grown in nutrient solution, were studied. Plants were treated with three levels of K supply (0.1, 1, 4 mM K+) and two levels of PEG (0, 25%). WUE was determined at leaf level (WUEL), at whole-plant level (WUEP), and via carbon isotope ratio (δ13C). Effects of assimilation and stomatal conductance on WUEL were evaluated and compared with effects of biomass production and whole-plant transpiration (EP) on WUEP. Adequate K supply enhanced WUEP up to 30% and by additional 20% under PEG stress, but had no effect on WUEL. EP was lower with adequate K supply, but this effect may be attributed to canopy microclimate. Shoot δ13C responded linearly to time-integrated WUEL in adequately supplied plants, but not in K-deficient plants, indicating negative effects of K deficiency on mesophyll CO2 diffusion. It is concluded that leaf-scale evaluations of WUE are not reliable in predicting whole-plant WUE of crops such as spring wheat suffering K deficiency. [ABSTRACT FROM AUTHOR]

The increasing probability of seasonal droughts and freshwater scarcity emphasizes the importance of crop traits such as water-use efficiency (WUE) and its relation to nutrient management. In an earlier study using soil substrate in a pot experiment, we reported significant positive effects of N supply on biomass WUE of tobacco. However, there was a debate that the latter may be due to indirect effects of N supply (hidden drought), most likely because plants supplied with adequate N generally have greater biomass and hence faster depletion of soil water in the root zone. In pot and in field situation, therefore, it is difficult to relate any variation in leaf or biomass WUE to the direct effect of N supply. In this context, the aim of the current study was to re-examine to what extent N fertilization directly affects biomass WUE and related parameters under non-limiting water supply in hydroponics. About 2 weeks after the transfer of tobacco seedlings into nutrient solution containing 2 mM N, plants were treated with high-N or low-N in the form of NH4NO3. A marked decrease in CO2 assimilation with low-N supply compared to high-N supply was measured already 5 d after onset of treatments (DAO). In contrast, three different experiments clearly showed that stomatal conductance (gs) remained almost constant until 5 DAO resulting in significantly lower leaf WUE under low-N compared to high-N. Leaf WUE decreased gradually (up to 42% lower leaf WUE) at later stages. Surprisingly, biomass WUE and whole-plant δ13C values were not affected by N supply at any harvest date, which is in contrast to our earlier report where we observed clearly positive effects of N supply on biomass WUE of the same tobacco variety in a pot experiment with soil substrate. Night-time respiration and transpiration rates (measured by gas exchange and thermal imaging) were significantly higher with high-N supply than with low-N supply. The data show that 48.6% and 9.8% of the beneficiary effect of N on daytime leaf WUE were lost when nocturnal stomatal conductance and night-time respiration of the same leaves were taken into consideration. Thus, we conclude that earlier reports showing positive effects of N supply on biomass WUE and δ13C values in soil or field experiments may be due to indirect effect of N supply ( e.g., hidden/mild drought). [ABSTRACT FROM AUTHOR]