Increasing nutrient inputs into terrestrial ecosystems affect not only plant communities but also associated soil microbial communities. Studies carried out in predominantly unmanaged ecosystems have found that increasing nitrogen (N) inputs generally decrease soil microbial biomass; less is known about long-term impacts in managed systems such as agroecosystems. The objective of this paper was to analyze the responses of soil microorganisms to mineral fertilizer using data from long-term fertilization trials in cropping systems. A meta-analysis based on 107 datasets from 64 long-term trials from around the world revealed that mineral fertilizer application led to a 15.1% increase in the microbial biomass (Cmic) above levels in unfertilized control treatments. Mineral fertilization also increased soil organic carbon (Corg) content and our results suggest that Corg is a major factor contributing to the overall increase in Cmic with mineral fertilization. The magnitude of the effect of fertilization on Cmic was pH dependent. While fertilization tended to reduce Cmic in soils with a pH below 5 in the fertilized treatment, it had a significantly positive effect at higher soil pH values. Duration of the trial also affected the response of Cmic to fertilization, with increases in Cmic most pronounced in studies with a duration of at least 20 years. The input of N per se does not seem to negatively affect Cmic in cropping systems. The application of urea and ammonia fertilizers, however, can temporarily increase pH, osmotic potential and ammonia concentrations to levels inhibitory to microbial communities. Even though impacts of fertilizers are spatially limited, they may strongly affect soil microbial biomass and community composition in the short term. Long-term repeated mineral N applications may alter microbial community composition even when pH changes are small. How specific microbial groups respond to repeated applications of mineral fertilizers, however, varies considerably and seems to depend on environmental and crop management related factors.

Long-term effects of mineral fertilizers on soil microorganisms – A review

This article provides a synthesis of literature values to trace the fate of 150 Tg/yr anthropogenic nitrogen applied by humans to the Earth's land surface. Approximately 9 TgN/yr may be accumulating in the terrestrial biosphere in pools with residence times of ten to several hundred years. Enhanced fluvial transport of nitrogen in rivers and percolation to groundwater accounts for approximately 35 and 15 TgN/yr, respectively. Greater denitrification in terrestrial soils and wetlands may account for the loss of approximately 17 TgN/yr from the land surface, calculated by a compilation of data on the fraction of N(2)O emitted to the atmosphere and the current global rise of this gas in the atmosphere. A recent estimate of atmospheric transport of reactive nitrogen from land to sea (NO(x) and NH(x)) accounts for 48 TgN/yr. The total of these enhanced sinks, 124 TgN/yr, is less than the human-enhanced inputs to the land surface, indicating areas of needed additional attention to global nitrogen biogeochemistry. Policy makers should focus on increasing nitrogen-use efficiency in fertilization, reducing transport of reactive N to rivers and groundwater, and maximizing denitrification to its N(2) endproduct.

https://www.pnas.org/content/pnas/106/1/203.full.pdf

On the fate of anthropogenic nitrogen

Potassium is one of the principle plant nutrients underpinning crop yield production and quality determination. While involved in many physiological processes, potassium's impact on water relations, photosynthesis, assimilate transport and enzyme activation can have direct consequences on crop productivity. Potassium deficiency can lead to a reduction in both the number of leaves produced and the size of individual leaves. Coupling this reduced amount of photosynthetic source material with a reduction in the photosynthetic rate per unit leaf area, and the result is an overall reduction in the amount of photosynthetic assimilates available for growth. The production of less photosynthetic assimilates and reduced assimilate transport out of the leaves to the developing fruit greatly contributes to the negative consequences that deficiencies of potassium have on yield and quality production. Goals aimed toward increasing crop productivity and improved quality dictate either increased potassium supply or more efficient use of potassium. Developing plants that more efficiently use potassium might be a worthwhile goal for geneticists.

Potassium influences on yield and quality production for maize, wheat, soybean and cotton.

Preface Part I. Farming Systems and Their Biological Components: 1. Agricultural systems 2. Trophic chains 3. Community concepts 4. Genetic resources 5. Development Part II. Physical and Chemical Environments: 6. Aerial environment 7. Soil resources Part III. Production Processes: 8. Nitrogen processes 9. Water relations 10. Photosynthesis 11. Respiration and partitioning Part IV. Resource Management: 12. Soil management 13. Strategies and tactics for rainfed agriculture 14. Water management in irrigated agriculture 15. Energy and labor Part V. Farming, Then, Now and in the Future: 16. Evolution of wheat farming systems in southern Australia 17. Technological change in high-yield agriculture 18. The future of agriculture Species list Conversions and constants useful in crop ecology Index.

Crop Ecology: Productivity and Management in Agricultural Systems

Soil management is fundamental to all agricultural systems and fertilization practices have contributed substantially to the impressive increases in food production. Despite the pivotal role of soil microorganisms in agro-ecosystems, we still have a limited understanding of the complex response of the soil microbiota to organic and mineral fertilization in the very long-term. Here we report the effects of different fertilization regimes (mineral, organic and combined mineral and organic fertilization), carried out for more than a century, on the structure and activity of the soil microbiome. Organic matter content, nutrient concentrations and microbial biomass carbon were significantly increased by mineral, and even more strongly by organic fertilization. Pyrosequencing revealed significant differences between the structures of bacterial and fungal soil communities associated to each fertilization regime. Organic fertilization increased bacterial diversity, and stimulated microbial groups (Firmicutes, Proteobacteria and Zygomycota) that are known to prefer nutrient-rich environments, and that are involved in the degradation of complex organic compounds. In contrast, soils not receiving manure harbored distinct microbial communities enriched in oligotrophic organisms adapted to nutrient-limited environments, as Acidobacteria. The fertilization regime also affected the relative abundances of plant beneficial and detrimental microbial taxa, which may influence productivity and stability of the agroecosystem. As expected, the activity of microbial exoenzymes involved in carbon, nitrogen and phosphorous mineralization were enhanced by both types of fertilization. However, in contrast to comparable studies, the highest chitinase and phosphatase activities were observed in the solely mineral fertilized soil. Interestingly, these two enzymes showed also a particular high biomass-specific activities and a strong negative relation with soil pH. As many soil parameters are known to change slowly, the particularity of unchanged fertilization treatments since 1902 allows a profound assessment of linkages between management and abiotic as well as biotic soil parameters. Our study revealed that pH and TOC were the majors, while nitrogen and phosphorous pools were minors, drivers for structure and activity of the soil microbial community. Due to the long-term treatments studied, our findings likely represent permanent and stable, rather than transient, responses of soil microbial communities to fertilization.

/pdf/mineral-vs-organic-amendments-microbial-community-structure-4wb4rxzsqn.pdf

Mineral vs. Organic Amendments: Microbial Community Structure, Activity and Abundance of Agriculturally Relevant Microbes Are Driven by Long-Term Fertilization Strategies

Smart poultry management: Smart sensors, big data, and the internet of things

Yield of both cultivars was closely associated with leaf K concentration and soil K availability, but response curves indicated a lower leaf and soil K requirement for the K-use-efficient cultivar. The K-use-efficient cultivar had a higher K uptake rate during fruit development and greater total K accumulation, particularly at low soil K levels. Defining the physiological bases for such large genetic variation in K use efficiency will help to identify why the cotton plant is more sensitive to K limitation than other crops and will aid breeding efforts to develop germplasm more tolerant of a limited soil K supply

Differential Response of Two Cotton Cultivars to Fertilizer and Soil Potassium

Acala (Gossypium hirsutum L.) and Pima (G. barbadense L.) cotton growth, lint yield, and fiber quality responses to N in the San Joaquin Valley, CA were evaluated. Numerous reasons, including adaptation of N fertilization guidelines to modern production practices, recent increases in energy costs, and growing concerns about NO3 contamination of ground water, led to the initiation of this study. Acala was grown for 3 yr on a Panoche day loam [fine-loamy, mixed (calcareous), thermic Typic Torriorthents] and a Wasco sandy loam (coarseloamy, mixed, nonacid, thermic Typic Torriorthents). Pima was grown for 2 yr on the Panoche clay loam. Four N treatments were established in a randomized complete block design: 56, 112, 168, and 224 kg N ha -1 . Three-year average aboveground dry matter production of Acala was 7800 and 12 600 kg ha -1 on the Panoche clay loam and 8500 and 11 900 kg ha -1 on the Wasco sandy loam for the 56 and 168 kg N ha -1 treatments, respectively. The equivalent 2-yr averages for Pima were 7600 (56 kg N ha -1 ) and 10 800 kg ha -1 (168 kg N ha -1 ). Linear increases in lint yield with increased N fertility level occurred for Acala on Panoche clay loam in every year. Maximum lint yield averaged over 3 yr was 1842 kg ha -1 in the 224 kg N ha -1 treatment. The response of Acala lint yield to N management on the Wasco sandy loam was smaller than on Panoche clay loam, with a maximum lint yield of 1666 kg ha -1 (224 kg N ha -1 , 3-yr average). Pima lint yield responded to N management in a quadratic fashion with maximum yields in the 168 kg N ha -1 treatment in both years (1638 kg ha -1 , 2-yr average). Acala gin turnouts were greater at the Panoche than at the Wasco site. Decreases in gin turnout with increasing N were significant on the Panoche clay loam (Acala and Pima) but not on the Wasco sandy loam (Acala). There was a generally positive relationship between increasing N fertilization and yield; however, efficient N management should include an assessment of available soil residual N, soil type, and yearly climatic conditions.

Response of Irrigated Acala and Pima Cotton to Nitrogen Fertilization

Although results from in vitro ovule culture studies have demonstrated a specific K requirement for fiber growth, a direct association between the K status of the cotton (L.) plant and fiber quality has not been established under field conditions. To evaluate this relationship, a single cultivar (1985) and two cultivars (1986 and 1987) were grown with 0, 120, 240, or 480 kg K ha in 10 blocked replicates of each K level on an irrigated, vermiculitic soil. There was a significant seed-cotton yield response to applied K in each year. Lint yield, however, increased relatively more than seed yield, resulting in a greater lint percentage as plant K supply increased. The greater lint percentage reflected increased fiber length and secondary wall thickness (measured as a micronaire index) obtained from plants that received fertilizer K. For both cultivars, the fiber length, micronaire index, fiber strength and percent elongation, and fiber length uniformity ratio (dependent variables) were each positively related to (i) fiber K concentration at maturity, (ii) leaf K concentration at early bloom, and (iii) an index of soil K availability as independent variables in regression analyses. Comparison of cultivar regressions, however, indicated that fiber quality of ‘Acala GC510’ was higher than that of ‘Acala SJ2’ at low fiber, leaf, or soil K levels. We conclude that K supply to cotton fruit is an important determinant of fiber quality under field conditions, and that the K requirement for producing high lint yield with acceptable quality may differ among genotypes.

Bruce A. Roberts

Papers

Smart poultry management: Smart sensors, big data, and the internet of things

Differential Response of Two Cotton Cultivars to Fertilizer and Soil Potassium

Response of Irrigated Acala and Pima Cotton to Nitrogen Fertilization

Potassium Nutrition Effects on Lint Yield and Fiber Quality of Acala Cotton

Soil Potassium Balance and Cumulative Cotton Response to Annual Potassium Additions on a Vermiculitic Soil