Exploring Overwintered Cover Crops as a Soil Management Tool in Upper-midwest High Tunnels

High tunnels are an important season extension tool for horticultural production in cold climates, however maintaining soil health in these intensively managed spaces is challenging. Cover crops are an attractive management tool to address issues such as decreased organic matter, degraded soil structure, increased salinity, and high nitrogen needs. We explored the effect of winter cover crops on soil nutrients, soil health and bell pepper (Capsicum annuum) crop yield in high tunnels for 2 years in three locations across Minnesota. Cover crop treatments included red clover (Trifolium pratense) monoculture, Austrian winter pea/winter rye biculture (Pisum sativum/Secale cereale), hairy vetch/winter rye/tillage radish (Vicia villosa/S. cereale/Raphanus sativus) polyculture, and a bare-ground, weeded control. Cover crop treatments were seeded in two planting date treatments: early planted treatments were seeded into a standing bell pepper crop in late Aug/early September and late planted treatments were seeded after bell peppers were removed in mid-September At termination time in early May, all cover crops had successfully overwintered and produced biomass in three Minnesota locations except for Austrian winter pea at the coldest location, zone 3b. Data collected include cover crop and weed biomass, biomass carbon and nitrogen, extractable soil nitrogen, potentially mineralizable nitrogen, microbial biomass carbon, permanganate oxidizable carbon, soil pH, soluble salts (EC), and pepper yield. Despite poor legume performance, increases in extractable soil nitrogen and potentially mineralizable nitrogen in the weeks following cover crop residue incorporation were observed. Biomass nitrogen contributions averaged 100 kg·ha−1 N with an observed high of 365 kg·ha−1 N. Cover crops also reduced extractable soil N in a spring sampling relative to the bare ground control, suggesting provision of nitrogen retention ecosystem services.

Identifying Sustainable Nitrogen Management Practices for Tea Plantations

Tea (Camellia sinensis L.) is the most widely consumed beverage in the world. It is mostly grown in the tropics with a heavy dependence on mineral nitrogen (N) fertilisers to maintain high yields while minimising the areas under cultivation. However, N is often applied in excess of crop requirements, resulting in substantial adverse environmental impacts. We conducted a systematic literature review, synthesising the findings from 48 studies to assess the impacts of excessive N application on soil health, and identify sustainable, alternative forms of N management. High N applications lead to soil acidification, N leaching to surface and groundwater, and the emission of greenhouse gases including nitrous oxide (N2O). We identified a range of alternative N management practices, the use of organic fertilisers, a mixture of organic and inorganic fertilisers, controlled release fertilisers, nitrification inhibitors and soil amendments including biochar. While many practices result in reduced N loading or mitigate some adverse impacts, major trade-offs include lower yields, and in some instances increased N2O emissions. Practices are also frequently trialled in isolation, meaning there may be a missed opportunity from assessing synergistic effects. Moreover, adoption rates of alternatives are low due to a lack of knowledge amongst farmers, and/or financial barriers. The use of site-specific management practices which incorporate local factors (for example climate, tea variety, irrigation requirements, site slope, and fertiliser type) are therefore recommended to improve sustainable N management practices in the long term.

Sorghum Agronomic Performance and Soil Chemical and Microbiological Properties as Influenced by Burkina Faso Phosphate Rock-Enriched Composts

Purpose The low availability of phosphorus (P) severely limits crop production in sub-Saharan Africa. We evaluated phosphate rock-enriched composts on soil properties and sorghum growth for use as environment-friendly fertilizers. Methods Treatments were sorghum straw, compost (Comp), Phosphate Rock (BPR), BPR-enriched compost (P-Comp), BPR-soil-enriched compost (P-Comp-Soil), nitrogen-phosphorus-potassium (NPK, 60-90-30), and control without phosphorus and organic material (CT). Sorgum straw and composts were applied at 1.34 tons ha-1. The amounts of nitrogen, phosphorus, and potassium in treatments, except in CT, were adjusted to 60, 90, 30 kg ha-1, with urea, BPR, and KCl, respectively. Sorghum vr. Kapelga was cultivated and soil samples were collected on days 52, 93, and 115 (harvest) for analysis. Results NPK and P-Comp-Soil provided the best sorghum yields. Soil available P was less in these treatments. P-Comp-Soil-amended soils recorded higher populations of bacteria (16S rRNA), acid phosphatase (aphA), phosphonatase (phnX), glucose dehydrogenase (gcd) and its cofactor pyrroloquinoline quinone (pqqE) genes. Phosphate-specific transporter (pstS) and arbuscular mycorrhizal fungi (AMF) abundances were generally higher in P-Comp-Soil soils, especially at the early growth stage. This active microbial activity in the P-Comp-Soil added to its initially higher available P justified a better nutrient uptake and yields comparable to NPK. Multivariate analysis also revealed the contribution of nitrogen, carbon, and exchangeable cations in sorghum growth. Conclusion This study demonstrated that direct phosphate rock application is not effective in sub-Saharan African upland cultivation. Alternative to chemical fertilizers, soils may be amended with phosphate rock-enriched composts, a niche of beneficial microbes improving soil health.

Long-Term Biosolids Application on Land: Beneficial Recycling of Nutrients or Eutrophication of Agroecosystems?

The impact of repeated application of alkaline biosolids (sewage sludge) products over more than a decade on soil concentrations of nutrients and trace metals, and potential for uptake of these elements by crops was investigated by analyzing soils from farm fields near Oklahoma City. Total, extractable (by the Modified Morgan test), and water-soluble elements, including macronutrients and trace metals, were measured in biosolids-amended soils and, for comparison, in soils that had received little or no biosolids. Soil testing showed that the biosolids-amended soils had higher pH and contained greater concentrations of organic carbon, N, S, P, and Ca than the control soils. Soil extractable P concentrations in the biosolids-amended soils averaged at least 10 times the recommended upper limit for agricultural soils, with P in the amended soils more labile and soluble than the P in control soils. Several trace elements (most notably Zn, Cu, and Mo) had higher total and extractable concentrations in the amended soils compared to the controls. A radish plant assay revealed greater phytoavailability of Zn, P, Mo, and S (but not Cu) in the amended soils. The excess extractable and soluble P in these biosolids-amended soils has created a long-term source of slow-release P that may contribute to the eutrophication of adjacent surface waters and contamination of groundwater. While the beneficial effects of increased soil organic carbon on measures of “soil health” have been emphasized in past studies of long-term biosolids application, the present study reveals that these benefits may be offset by negative impacts on soils, crops, and the environment from excessive nutrient loading.