Nitrogen (N) fertilizer use efficiency can be improved when nonfertilizer N inputs, including N mineralization from soil organic matter, can be quantified accurately. The objectives of this study were (i) to calculate annual N mineralization rates based on a budget for organic N inputs and outputs for soils under annual crops in California's Central Valley and (ii) to compare the results with temperature‐ and moisture‐adjusted N mineralization rates from a laboratory incubation. The organic‐N budget included organic N inputs from aboveground crop residues, roots, and root exudates as well as long‐term changes in soil organic N. A 10‐wk laboratory incubation was performed at 25°C and optimal moisture content with undisturbed soil cores collected pre‐plant in spring 2016 and 2017 from 30 field sites. The sites had no recent history of cover crops, manure, or compost applications. Based on the organic‐N budget, annual N mineralization rates in the top 30 cm of the profile ranged from 76 to 123 kg ha−1 yr−1. Taking soil moisture and temperature in furrow‐irrigated fields into account, approximately half of this amount was mineralized during a cropping season from mid‐April to mid‐August. Even when corrected for daily temperature and moisture content, N mineralization rates in the incubation study were considerably higher than the rates estimated with the organic‐N budget. The organic‐N budget provides an estimate of the annual N mineralization rates in these soils. Adjustments for soil properties and crop management will likely improve estimates for individual sites.
Core Ideas
Annual N mineralization rates were calculated with an organic‐N budget.
Calculated annual N mineralization rates ranged from 76 to 123 kg ha−1.
A laboratory incubation overestimated N mineralization.
California Blackeye 77' (CB77) (Reg. no. CV-344, PI 698656) is a blackeye-type cowpea [Vigna unguiculata (L.) Walp] cultivar developed by the University of California, Riverside. CB77 is distinguished from the industry standard cultivars, 'California Blackeye 46' (CB46) and 'California Blackeye 5' (CB5), by its ability to resist infestation caused by cowpea aphid (Aphis craccivora Koch), a destructive sap-sucking insect pest prevalent in the Central Valley of California and warm-to-hot regions worldwide. CB77 was developed by introgression of two known quantitative trait loci for aphid resistance from the African cowpea breeding line IT97K-556-6 into CB46 through marker-assisted backcrossing. Genotyping with 51,128 single nucleotide polymorphism markers reveals that CB77 is near-isogenic to CB46 and carries two resistance haplotypes (∼4 Mb in total) from IT97K-556-6. On-station and on-farm trials with aphid infestations confirmed the inherent resistance in CB77 (aphids covered 0-10% of plant surface area without causing any crown damage, whereas check CB46 had aphids covering 60-70% of plant surface area and causing severe crown damage). Under protected conditions, CB77 showed grain yield, seed quality, and other agronomic characteristics equivalent to CB46 and better yield than CB5. CB77 could therefore be substituted for CB46 and CB5 in production regions where aphids are present. The near-isogenic pair CB77 and CB46 are also useful materials for resistance gene discovery.
INTRODUCTIONBlackeye bean, also known as black-eyed pea, is a type of cowpea [Vigna unguiculata (L.) Walp], a food legume native to Africa where it provides a primary source of protein that Abbreviations: MABC, marker-assisted backcrossing; QTL, quantitative trait locus; RCBD, randomized complete block design; SNP, single nucleotide polymorphism; UC-
Agronomic cropping systems in many regions face growing economic and management challenges as well as new regulations designed to address negative environmental and social externalities. At the same time, public support for agricultural education and extension is decreasing. Hence, new approaches are necessary to understand the most pressing on-farm issues and help prioritize critical needs. With a diversity of agronomic crops and new regulations for water and nitrogen, California is an important case study for other regions. The objective of this study was to identify major grower and industry concerns, management challenges, and motivations in making management decisions. In 2020, 483 growers, consultants, and allied industry of agronomic crop production responded to an online survey. The crops most widely grown by respondents included rice (Oryza sativa L.), alfalfa (Medicago sativa L.), wheat (Triticum aestivum L.), and corn (Zea mays L.). Four out of the five top concerns were related to water. Weed control and irrigation/water management were primary management challenges, though differences occurred by crop and region. The highest priorities considered in grower management decision-making were water, profitability, and land stewardship. Crop rotation benefits were a primary reason for growing agronomic crops, with profitability and tradition ranking closely behind. This study highlights opportunities to guide research and extension efforts based on critical needs identified by growers and industry, while also informing larger policy and institutional decisions regarding new programs and funding to address key issues in agronomic crop production.
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