Potentially Mineralizable N Research Articles

The response of a sorghum sudangrass cover crop to residual nitrogen and its relationship with spectral sensors

AbstractA sorghum sudangrass (SSG) cover crop grown after a cash crop could take up residual nitrogen (N) before it is lost. As in‐field monitoring of SSG properties is laborious, predicting biomass and N concentrations with spectral sensors could be useful. At two sites in Live Oak, Florida, we evaluated the response of SSG to residual N from previous N fertilization and the performance of handheld and satellite sensors in estimating SSG properties. We quantified aboveground biomass, plant N, leaf greenness (NDVI), net potential N mineralization (PNM), and soil permanganate oxidizable carbon (POXC). Residual N did not affect SSG properties, PNM was highest at the highest N input rate in one site, and soil POXC was correlated with SSG properties (biomass and plant N). NDVI measured from a handheld sensor better predicted SSG properties than satellite imagery in these small plots, suggesting a greater potential to be a useful management tool.

Soil carbon and nitrogen responses to forage cropping systems following irrigation retirement

AbstractLimited annual precipitation and increasing scarcity of irrigation water are forcing farmers in arid and semi‐arid regions to convert irrigated fields into dryland farming, yet their impacts on soil carbon (C) and nitrogen (N) fractions are not fully understood. This study evaluated changes in soil C and N fractions and forage production under four cropping systems after irrigation retirement in a semi‐arid condition. Treatments included an annual winter wheat forage (Triticum aestivum L.) (AWW), a perennial wheat (PW) forage (T. aestivum L. × Thinopyrum spp.) (PW), a mixture of native grasses (NG), and a pasture crop (PC = AWW and NG mixture). Evaluation of various soil C and N fractions, forage dry matter yield, and nutritive value parameters suggested that soil inorganic N and potentially mineralizable N (PMN) were 38%–45% and 36%–44% greater in autumn 2020 and 62%–68% and 46%–55% greater in spring 2021 under AWW and PW, respectively, than NG and PC. Soil potentially mineralizable carbon (PMC) was 58%–129% and 64%–138% greater under NG and PW than AWW and PC. The responses of other soil C and N fractions varied with soil sampling dates but not with crops or crop × sampling date interaction. Total forage dry matter yield was 4016, 7849, 12,517, and 13,869 kg ha−1 for AWW, PW, PC, and NG, respectively, and PW had the best forage nutritive value. These results suggest soil C and N mineralization could be enhanced by adopting perennial systems, including NG, PW, and PC, while PW maintains good‐quality forage production.

Do cover crops on the Canadian prairies affect soil nitrogen cycling?

For one of Canada’s most important regions of crop production—the prairies—it’s uncertain if cover crops can be successfully integrated into rotations; if so, will soil nitrogen (N) cycling be influenced to benefit main crops? To address these gaps, we compared a crop rotation with cover crops (CC) vs. without cover crops (LR) from 2018 to 2021 in Saskatoon, SK. The main crops were grown in sequence of wheat–canola–potato–pea; the cover crops included red clover, berseem clover/oat mix, fall rye, and a brassica cover. Yield and aboveground biomass were collected each year and analyzed to determine crop yield and N use efficiency (NUE). Soil N availability was monitored in various ways, that is, by assessing pre-plant soil nitrate, soil inorganic N (SIN) supply rate, and potentially mineralizable N (PMN). We found that the influence on soil N dynamics was restricted to the non-growing season where cover crops reduced SIN supply rate and nitrate content compared to the conventional practice without cover crops. Yet, rotations with vs. without cover crop did not differ in crop NUEs, yields, or in-season N dynamics. We found some evidence that diversifying rotations with cover crops may help the system to function more like perennial systems in terms of regulating N in the long run; but had limited impact during the three years studied. To ensure that cover crops are effective and functional on the prairies, innovative design approaches are needed to adapt cover crops to reach soil health goals under prairie conditions.

Elucidating the impact of boron fertilization on soil physico-chemical and biological entities under cauliflower-cowpea-okra cropping system in an Eastern Himalayan acidic Inceptisol.

Information on the role of boron (B) on soil physico-chemical and biological entities is scarce, and the precise mechanism in soil is still obscure. Present field investigation aimed to assessing the implication of direct and residual effect of graded levels of applied-B on soil biological entities and its concomitant impact on crop productivity. The treatments comprised of five graded levels of B with four replications. To assess the direct effect of B-fertilization, cauliflower was grown as a test crop wherein, B-fertilization was done every year. For assessment of succeeding residual effects of B-fertilization, cowpea and okra were grown as test crops and, B-fertilization was phased out in both crops. The 100% recommended dose of NPK (RDF) along with FYM was uniformly applied to all crops under CCOCS. Results indicated that the direct effect of B had the edge over residual effect of B in affecting soil physico-chemical and biological entities under CCOCS. Amongst the graded levels of B, application of the highest B level (2 kg ha-1) was most prominent in augmenting microbiological pools in soil at different crop growth stages. The order of B treatments in respect of MBC, MBN, and soil respiration at different crop growth stages was 2.0 kg B ha-1 > 1.5 kg B ha-1 > 1.0 kg B ha-1 > 0.5 kg B ha-1 > 0 kg B ha-1, respectively. Moreover, maximum recoveries of potentially mineralizable-C (PMC) and potentially mineralizable-N (PMN) were noticed under 2 kg B ha-1. Analogous trend was recorded in soil microbial populations at different crop growth stages. Similarly, escalating B levels up to 2 kg B ha-1 exhibited significantly greater soil enzymatic activities viz., arylsulphatase (AS), dehydrogenase (DH), fluorescein diacetate (FDA) and phosphomonoesterase (PMA), except urease enzyme (UE) which showed an antagonistic effect of applied-B in soil. Greater geometric mean enzyme activity (GMEA) and soil functional diversity index were recorded under 2 kg B ha-1 in CCOCS, at all crop growth stages over control. The inclusive results indicated that different soil physico-chemical and biological properties CCOCS can be invariably improved by the application of graded levels of B up to 2 kg B ha-1 in an acid Inceptisol.

Soil Organic Matter Storage in Irrigated Tsitsikamma Dairy Farms with Minimum Tilled Pasture Mixtures: Case Studies

In recent years, pasture production changed from conventional tilled single pastures to minimum tilled mixed pastures in the Tsitsikamma region, South Africa. However, storage of soil organic matter (SOM) under minimum tilled mixed pastures is not yet quantified. This study evaluated SOM indices in the upper 60 cm soil of six-year-old mixed pastures in the Upper (UT) and Lower (LT) Tsitsikamma regions. Soil samples were collected at 0–15, 15–30, 30–45, and 45–60 cm soil layers of five farms (F1, F2, F3, F4, and F5) treated with different rates of fertilizer (NPK) alone and in combination with dairy effluent (DE) and/or poultry manure (PM). Results of this study indicated that there were no significant differences in bulk density, total nitrogen (N), and rate of potentially mineralizable N (PMN) between farms in the UT region. In the LT region, NPK, DE, and PM combinations improved soil C accumulation relative to the soil application of NPK. Higher C/N ratios in the LT region suggested adequate C for microbial energy and maintenance. Integrating manure into minimum tilled pasture mixtures as a replacement for synthetic fertilizers seems to be a feasible option to promote SOM storage, but remains only feasible by applying site-specific management strategies.

Legume Cover Crop Contributions to Ecological Nutrient Management in Upper Midwest Vegetable Systems

Cover cropping, especially with legumes, is a critical approach to ecological soil nutrient management as a means to meet Sustainable Development Goal (SDG) 2, addressing food security issues via sustainable agriculture approaches. However, cover cropping in some of the most intensified food production regions of the northern U.S. is challenged by short growing seasons and harsh winters with variable temperatures and increasingly erratic snowfall. In this study, we explore the potential of winter annual legume cover crops to augment soil organic carbon (C) and nitrogen (N) stocks within a horticultural cropping system under climate conditions that allow only modest cover crop biomass production. We compared hairy vetch, cereal rye, red clover, and a hairy vetch/rye biculture in a randomized complete block design at two sites (North Central and Southwest Research and Outreach Centers in Minnesota) over 2 years. Cover crops were established in fall and terminated in spring prior to sweet corn planting, and soils sampled both at pre-cover crop termination and 2 weeks post-termination. We determined several indicators of C and N dynamics, including microbial biomass C (MBC), permanganate-oxidizable C (POXC), particulate organic matter C and N (POMC and POMN, respectively), extractable soil N (EXTN), and potentially mineralizable N (PMN). Out of all treatments evaluated, vetch production increased soil EXTN the greatest after 2 weeks, contributing two to 11 times more EXTN to soils compared to non-vetch treatments, meeting N requirements for sweet corn in three out of four site-years. Overall, time of sampling, either pre-or post-termination, consistently impacted soil measurements, with p < 0.05 in 20 out of 24 soil parameter × site-year combinations. Study results suggest that cover crops planted in colder northern climates during winter fallow periods can supply valuable N following spring termination, but termination effects on labile C and N pools are mixed. Our findings advance understanding of how cover cropping can support SDG 2 outcomes by assessing cover crop legume systems under biophysical conditions that challenge cover crop integration in agroecosystems.

Soil nitrogen cycling under contrasting management systems in Amazon Coffea canephora agroecosystems

AbstractRobusta coffee (Coffea canephora Pierre ex Froehner) is well suited to the humid tropical climate of the Amazon basin. It is often produced under contrasting conditions of low‐input agroforestry systems and intensively managed monocultures that differ in N constraints on productivity. We evaluated indicators of soil N cycling and coffee plant N sufficiency using a full factorial of two input managements (organic vs. conventional) and the absence or presence of the interplanted leguminous tree (LT) Erythrina spp. in a replicated robusta coffee field trial in the Ecuadorian Amazon. Activities of soil protease, three aminopeptidases, N‐acetyl‐β‐D‐glucosaminidase, cellobiohydrolase, and β‐glucosidase were evaluated in tandem with soil NH4–N and NO3–N, potentially mineralizable N (PMN), and permanganate oxidizable C (POXC), as well as coffee leaf N, leaf N/P ratio (N/P), and yield. The LT decreased soil enzyme activities, PMN, and extractable NH4–N, as well as leaf N and leaf N/P. Enzyme activities and NH4–N were greater under organic input, but conventional input resulted in greater PMN, leaf N, leaf N/P, and yield. Permanganate oxidizable C and NO3–N were similar across input and interplanting but were more variable in the presence of LT relative to its absence. Lower soil enzymatic activities, labile N pools, and leaf N in coffee systems with Erythrina spp. suggest that, although a common smallholder practice in this region, interplanting this leguminous perennial has marginal impacts on soil N cycling and may not necessarily improve N supply for robusta coffee.

Long-term biosolids land application influences soil health

Soil health assessments associated with organic amendment applications have primarily focused attention on manure or composts. Yet, quantifying specific changes in soil health associated with biosolids land applications has yet to be determined. Our objectives were to evaluate the changes in various soil indicators, and utilizing the Soil Management Assessment Framework (SMAF), quantify changes in soil indicator scores and soil health indices as affected by either increasing inorganic N fertilizer (0 up to 112 kg N ha−1) or biosolids (0 up to 11.2 dry Mg ha−1) applied every other year over 22 years. Soils were sampled (0 to 20 cm depth) following 22 years of N fertilizer or biosolids inputs to a dryland wheat-fallow (Triticum aestivum L.) rotation, 11 soil health indicators were monitored under SMAF guidelines, and indicators, indicator scores, and soil health indices were analyzed statistically. In general, increasing N fertilizer application rates had little effect on soil indicators, SMAF indicator scores or soil health indices. Increasing biosolids application rates increased soil organic C (SOC) and potentially mineralizable N (PMN). The SMAF indicator scores showed upward trends for soil pH, SOC, PMN, and microbial biomass C (MBC) associated with increasing biosolids application rates; discussing trends are important as these indicator scores are combined to provide soil health indices. Indeed, increasing biosolids application rates increased soil chemical and biological health indices, leading to an improvement in the overall soil health index. When comparing the overall N fertilizer to biosolids effect, biosolids applications significantly improved the soil biological health index. Results indicate that long-term biosolids land application to semi-arid, dryland wheat fallow rotations, similar to those studied, improve various aspects of soil health. These findings suggest that biosolids may play a pivotal role in dryland agroecosystem sustainability.

Extending Cover Crop Benefits with Zone Till Management in Northern Organic Summer Squash Production

Winter annual legume cover crops often fail to reach full maturity by spring vegetable planting dates in northern climates, which prevents maximum nitrogen (N) contributions. To determine if delayed termination improved cover crop biomass and N content, we evaluated winter rye + hairy vetch (Secale cereale L. + Vicia villosa Roth) and oat + field pea (Avena sativa L. + Pisum sativum L.) cover crop mixtures in 2015 and 2016, and medium red clover (Trifolium pratense L.) in 2016, in zone-tilled organic yellow crookneck squash (Cucurbita pepo var. torticollis Harz). In-row regions where cover crops were terminated in early spring during crop row preparation were compared to between-row regions where termination was delayed until legume maturation in late spring. Soil quality (soil inorganic N, permanganate oxidizable C (POXC), and potentially mineralizable N (PMN)) was also determined for in-row and between-row regions at four time points throughout the growing season. In 2015, winter rye + hairy vetch biomass N more than doubled between early and late termination times, with 120 and 258 kg N ha−1, respectively. Permanganate oxidizable C was not responsive to cover crop systems or tillage, and only slightly decreased over time in 2016. Soil inorganic N and PMN after cover crop termination in 2016 provided evidence of localized soil N cycling responses to cover crop termination in in-row and between-row regions. The extended growing period for cover crops between crop rows in the first several weeks of crop growth had no negative effect on crop yield, and appeared to enhance soil fertility.

Interrelationships of Chemical, Physical and Biological Soil Health Indicators in Beef-Pastures of Southern Piedmont, Georgia

The study of interrelationships among soil health indicators is important for (i) achieving better understanding of nutrient cycling, (ii) making soil health assessment cost-effective by eliminating redundant indicators, and (iii) improving nitrogen (N) fertilizer recommendation models. The objectives of this study were to (i) decipher complex interrelationships of selected chemical, physical, and biological soil health indicators in pastures with history of inorganic or broiler litter fertilization, and (ii) establish associations among inorganic N, potentially mineralizable N (PMN), and soil microbial biomass (SMBC), and other soil health indicators. In situ soil respiration was measured and soil samples were collected from six beef farms in 2017 and 2018 to measure selected soil health indicators. We were able to establish associations between easy-to-measure active carbon (POXC) vs. PMN (R2 = 0.52), and N (R2 = 0.43). POXC had a noteworthy quadratic relationship with N and nitrate, where we found dramatic increase of N and nitrate beyond an inflection point of 500 mg kg−1 POXC. This point may serve as threshold for soil health assessment. The relationships of loss-on-ignition (LOI) carbon with other soil health indicators were discernable between inorganic- and broiler litter-fertilized pastures. We were able to establish association of SMBC with other soil variables (R2 = 0.76) and there was detectable difference in SMBC between inorganic-fertilized and broiler litter-fertilized pastures. These results could be useful for cost-effective soil health assessment and optimization of N fertilizer recommendation models to improve N use efficiency and grazing system sustainability.

Adjusting corn nitrogen management by including a mineralizable‐nitrogen test with the preplant and presidedress nitrate tests

AbstractThe anaerobic potentially mineralizable N (PMN) test combined with the preplant (PPNT) and presidedress (PSNT) nitrate tests may improve corn (Zea mays L.) N fertilization predictions. Forty‐nine corn N response experiments (mostly corn following soybean [Glycine max (L.) Merr.]) were conducted in the U.S. Midwest from 2014–2016 to evaluate the ability of the PPNT and PSNT to predict corn relative yield (RY) and N fertilizer over‐ and under‐application rates when adjusted by PMN. Before planting and N fertilization, PPNT (0–30, 30–60, and 60–90 cm) and PMN (0–30 cm) samples were obtained. In‐season soil samples were obtained at the V5 development stage for PSNT (0–30, 30–60 cm) in all N rate treatments and PMN (0–30 cm) in only the 0 and 180 kg N ha−1 preplant N treatments. Increasing NO3–N sampling depths beyond 30 cm with or without PMN improved RY predictability marginally (R2 increase up to 0.20) and reduced over‐ and under‐application frequencies up to 14%. Including PMN (preplant only) with PPNT or PSNT improved RY predictability minimally (R2 increase up to 0.10) only for coarse‐ and medium‐textured soils, but N fertilizer over‐ and under‐application frequencies were not substantially reduced (≤12%). These marginal improvements in RY predictability and N fertilizer over‐ and under‐application frequencies, regardless of the variables used (e.g., fertilization, sampling depth, soil texture, and growing degree‐day categories), demonstrate that including PMN with soil NO3–N alone does not improve corn N fertilization need predictions enough to recommend their use.

Soil sample timing, nitrogen fertilization, and incubation length influence anaerobic potentially mineralizable nitrogen

AbstractUnderstanding the variables that affect the anaerobic potentially mineralizable N (PMNan) test should lead to a standard procedure of sample collection and incubation length, improving PMNan as a tool in corn (Zea mays L.) N management. We evaluated the effect of soil sample timing (preplant and V5 corn development stage [V5]), N fertilization (0 and 180 kg ha−1) and incubation length (7, 14, and 28 d) on PMNan (0–30 cm) across a range of soil properties and weather conditions. Soil sample timing, N fertilization, and incubation length affected PMNan differently based on soil and weather conditions. Preplant vs. V5 PMNan tended to be greater at sites that received < 183 mm of precipitation or < 359 growing degree‐days (GDD) between preplant and V5, or had soil C/N ratios > 9.7:1; otherwise, V5 PMNan tended to be greater than preplant PMNan. The PMNan tended to be greater in unfertilized vs. fertilized soil in sites with clay content > 9.5%, total C < 24.2 g kg−1, soil organic matter (SOM) < 3.9 g kg−1, or C to N ratios < 11.0:1; otherwise, PMNan tended to be greater in fertilized vs. unfertilized soil. Longer incubation lengths increased PMNan at all sites regardless of sampling methods. Since PMNan is sensitive to many factors (sample timing, N fertilization, incubation length, soil properties, and weather conditions), it is important to follow a consistent protocol to compare PMNan among sites and potentially use PMNan to improve corn N management.

Plant growth drives soil nitrogen cycling and N-related microbial activity through changing root traits

Abstract Relationships between plants and nitrogen-related microbes may vary with plant growth. We investigated these dynamic relationships over three months by analyzing plant functional traits (PFT), arbuscular mycorrhizal fungal (AMF) colonization, potential N mineralization (PNM), potential nitrification (PNA) and denitrification activities (PDA) in Dactylis glomerata cultures. D. glomerata recruited AMF during early growth, and thereafter maintained a constant root colonization intensity. This may have permitted high enough plant nutrient acquisition over the three months as to offset reduced soil inorganic N. PFT changed with plant age and declining soil fertility, resulting in higher allocation to root biomass and higher root C:N ratio. Additional to root AMF presence, PFT changes may have favored denitrification over mineralization through changes in soil properties, particularly increasing the quality of the labile carbon soil fraction. Other PFT changes, such as N uptake, modified the plants’ ability to compete with bacterial groups involved in N cycling.

Soil quality assessment based on soil organic matter pools under long‐term tillage systems and following tillage conversion in a semi‐humid region

AbstractA field study was conducted to assess the long‐term effects of no‐tillage (NT) and conventional tillage (CT), and the short‐term effects following tillage conversion from CT to NT (NTn) and from NT to CT (CTn) on soil quality (SQ) indicators in a semi‐humid climate. First, plots of a long‐term tillage experiment on a Luvic Phaeozem initiated in 1986 were split into two subplots in 2012, yielding four treatments: NT, CT, NTn and CTn. In 2015, composite soil samples were collected from each treatment and from a natural site (Ref) at depths 0–5, 5–10, 10–20 and 0–20 cm. Several indicators were determined: soil organic carbon (SOC) and nitrogen (SON); particulate organic C (POM‐C) and N (POM‐N); potential N mineralization (PMN) and soil respiration (Rs). Moreover, bulk density was determined in long‐term tillage systems. Different ratios between indicators were calculated, with emphasis on its function in the agroecosystem, that is functional indicators. Significant differences in SOC, SON and PMN were found between CT and NT at most depths. In contrast, 3 years after tillage conversion, only a part of the SQ indicators studied were modified mainly at the 0–10 cm depth. The functional indicators showed differences between tillage systems in the long‐term and after short‐term tillage conversion depending on the depth; however, the PMN/SON ratio demonstrated differences at all depths. Under these conditions, this ratio‐related to easily mineralizable N fraction proved to be a promising indicator for assessing SQ under contrasting tillage systems regardless of the sampling depth.

Predicting Economic Optimal Nitrogen Rate with the Anaerobic Potentially Mineralizable Nitrogen Test

Estimates of mineralizable N with the anaerobic potentially mineralizable N (PMNan) test could improve predictions of corn (Zea mays L.) economic optimal N rate (EONR). A study across eight US midwestern states was conducted to quantify the predictability of EONR for single and split N applications by PMNan. Treatment factors included different soil sample timings (pre‐plant and V5 development stage), planting N rates (0 and 180 kg N ha−1), and incubation lengths (7, 14, and 28 d) with and without initial soil NH4–N included with PMNan. Soil was sampled (0–30 cm depth) before planting and N application and at V5 where 0 or 180 kg N ha−1 were applied at planting. Evaluating across all soils, PMNan was a weak predictor of EONR (R2 ≤ 0.08; RMSE, ≥67 kg N ha−1), but the predictability improved (15%) when soils were grouped by texture. Using PMNan and initial soil NH4–N as separate explanatory variables improved EONR predictability (11–20%) in fine‐textured soils only. Delaying PMNan sampling from pre‐plant to V5 regardless of N fertilization improved EONR predictability by 25% in only coarse‐textured soils. Increasing PMNan incubations beyond 7 d modestly improved EONR predictability (R2 increased ≤0.18, and RMSE was reduced ≤7 kg N ha−1). Alone, PMNan predicts EONR poorly, and the improvements from partitioning soils by texture and including initial soil NH4–N were relatively low (R2 ≤ 0.33; RMSE ≥ 68 kg N ha−1) compared with other tools for N fertilizer recommendations.Core Ideas Anaerobic potentially mineralizable N (PMNan) is a weak predictor of economic optimal N rate (EONR). Predictability of EONR by PMNan improves when accounting for soil texture. For coarse‐textured soils, PMNan at V5 improves EONR predictability. Increasing incubation length does not substantially improve EONR predictability. PMNan alone is not a reliable management tool for N rate determination.

Increasing Labile Soil Carbon and Nitrogen Fractions Require a Change in System, Rather Than Practice

The influence of tillage, carbon (C) and nitrogen (N) inputs and perennialization on labile fractions of soil organic matter (SOM) has been widely investigated, but research on the temporal and depth variation of labile C and N fractions in long‐term agroecosystems representative of the US Corn Belt is lacking. In this study, labile soil fractions as influenced by different agriculture management approaches common in the north‐central United States were characterized through measurements of potentially mineralizable N (PMN), mineralizable C (C‐min), and permanganate oxidizable C (POXC), which are known indicators of the biologically active pool of SOM. Soils were sampled five times in six different cropping systems at the Wisconsin Integrated Cropping Systems Trial: three annual cropping systems (continuous corn, strip‐till corn–soybean, organic grain) and three forage cropping systems (conventional forage, organic forage, grazed pasture). Across all sampling dates (May–September) and soil depth (0–15 and 15–30 cm), forage‐based cropping systems generally had greater PMN, C‐min, and POXC, with C‐min and PMN expressing the largest differences between forage and grain‐based cropping systems. Labile soil C and N fractions across cropping systems were typically greatest in July or August and were ∼50% greater in the top 0 to 15 cm of soil than the 15 to 30 cm. These results suggest sampling timing and depth for PMN, POXC, and C‐min need to be standardized to optimize their use as soil health indicators and that shifts in the system toward perenniality will be required to increase labile C and N fractions on the highly fertile Mollisols of the US Corn Belt.

United States Midwest Soil and Weather Conditions Influence Anaerobic Potentially Mineralizable Nitrogen

Nitrogen provided to crops through mineralization is an important factor in N management guidelines. Understanding of the interactive effects of soil and weather conditions on N mineralization needs to be improved. Relationships between anaerobic potentially mineralizable N (PMNan) and soil and weather conditions were evaluated under the contrasting climates of eight US Midwestern states. Soil was sampled (0–30 cm) for PMNan analysis before pre‐plant N application (PP0N) and at the V5 development stage from the pre‐plant 0 (V50N) and 180 kg N ha−1 (V5180N) rates and incubated for 7, 14, and 28 d. Even distribution of precipitation and warmer temperatures before soil sampling and greater soil organic matter (SOM) increased PMNan. Soil properties, including total C, SOM, and total N, had the strongest relationships with PMNan (R2 ≤ 0.40), followed by temperature (R2 ≤ 0.20) and precipitation (R2 ≤ 0.18) variables. The strength of the relationships between soil properties and PMNan from PP0N, V50N, and V5180N varied by ≤10%. Including soil and weather in the model greatly increased PMNan predictability (R2 ≤ 0.69), demonstrating the interactive effect of soil and weather on N mineralization at different times during the growing season regardless of N fertilization. Delayed soil sampling (V50N) and sampling after fertilization (V5180N) reduced PMNan predictability. However, longer PMNan incubations improved PMNan predictability from both V5 soil samplings closer to the PMNan predictability from PP0N, indicating the potential of PMNan from longer incubations to provide improved estimates of N mineralization when N fertilizer is applied.Core Ideas Relationships between mineralization estimates taken with the PMNan test and soil and weather conditions need to be improved. Soil sample timing and N fertilization minimally affected PMNan predictability by soil and weather parameters. Soil properties predict PMNan better than weather conditions. Soil and weather conditions combined explain up to 69% of the variability of PMNan. Longer PMNan incubations improve the relationship between soil and weather parameters and PMNan after N fertilization.

Linking Soil Health to Sustainable Crop Production: Dairy Compost Effects on Soil Properties and Sorghum Biomass

Dairy compost is utilized in agricultural fields to supplement nutrients, yet its role in optimizing nutrient supply and health of semiarid soils is not clear. A greenhouse study was conducted over two months to evaluate soil properties and forage sorghum production under various compost rates. The study had six treatments and four replications. Treatments included compost application rates at 6.7 (C1), 13.5 (C2), 20.2 (C3), 26.9 (C4), and 33.6 Mg ha−1 (C5) and a control (C0). Soil samples were analyzed for soil organic carbon (SOC), potentially mineralizable carbon (PMC), total nitrogen (N), inorganic N, potentially mineralizable N (PMN), available phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and sulfur (S). Plant biomass production and biomass C, N, and lignin contents were also estimated. High compost rates improved soil properties significantly (p < 0.05) indicated by increased SOC, N, P, K, Ca, and cation exchange capacity (CEC). Sorghum biomass production did not increase significantly with compost rate, while shoot N content increased at higher rates of compost. A nutrient management plan that integrates dairy compost application has potential to improve soil health and support sustainable forage production in semiarid regions.

Assessment of In‐Season Soil Nitrogen Tests for Corn Planted into Winter Annual Cover Crops

Core Ideas The Solvita 1‐d CO2 mineralization test could be a new tool to improve in‐season N rate recommendations for corn. Solvita and soil NO3–N tests may be useful for predicting the level of early‐season N mineralization from winter cover crops (WCCs). Soil NO3–N collected at the V4 growth stage of corn at 0 to 15 cm was positively correlated (R2 = 0.45) with corn check yield. Neither the Solvita nor the presidedress nitrate test detected WCC N mineralization consistently enough to use them in rate recommendations. Environmental and economic goals encourage the use of soil N tests to improve fertilizer N (FN) management in corn (Zea mays L.). Recently, the Solvita 1‐d CO2 burst test, which proposes to estimate soil potentially mineralizable N (PMN), has been promoted as a tool for FN recommendations. We aimed to compare the Solvita test with the established presidedress nitrate test (PSNT) for estimating optimum sidedressed FN rates in a typical corn crop rotation in the Mid‐Atlantic United States that includes winter annual cover crops (WCCs). Research was conducted at eight locations from 2012 to 2014. Three WCC treatments [cereal rye (Secale cereale L.), hairy vetch (Vicia villosa Roth ssp. villosa) or a cereal rye–hairy vetch mix] were the main plots and 10 FN rates were the subplots. The WCCs affected preplanting (PP) Solvita results at one location, V4 NO3–N at 0 to 15 cm (PSNT15) at four locations, and V4 NO3–N at 0 to 30 cm (PSNT30) at two locations. Correlations between soil N test parameters and relative corn yields ranged from 0.31 to 0.13. Values for PSNT15 and PSNT30 correlated positively with corn check yields (r = 0.41 and 0.39 respectively). Solvita did not provide additional information to PSNT for predicting preplanting PMN, V4 PMN, or corn check yields. The advantages of the Solvita test were its simplicity, speed of analysis, and lower coefficient of variation relative to the PSNT. Neither method was consistently effective for predicting WCC effects on soil N or relative corn yield.

Developing Near‐ and Mid‐Infrared Spectroscopy Analysis Methods for Rapid Assessment of Soil Quality in Illinois

Core Ideas Lithology‐based libraries may support reusable NIR models to predict soil quality. Monte Carlo feature selection and spectral refinement of NIR‐ and MIR‐based models. Use of randomly drawn validation datasets and overestimation of RPD. Estimation of plant growth via NDVI and relation to NIR‐ and MIR‐based models. Rapid, affordable assessment of soil quality (SQ) is needed to maintain soil health. We sought to build reusable near‐ (NIR) and mid‐infrared‐ (MIR) based models using a regional library of accepted SQ indicators and Normalized Difference Vegetation Index (NDVI). This described soil health in 228 topsoil samples from 57 grain fields in Illinois paired to compare the influence of conventional, organic or conservation‐tillage practices. Predictive models for all SQ indicators were developed with Partial Least Squares Regression (PLSR) using: (i) whole NIR or MIR spectra, (ii) refined spectra that included features associated with organic functional groups, or (iii) refined spectra that were identified as important using Monte Carlo feature selection (MCFS). Comparison of model building methods using randomly or systematically divided calibration and validation sets suggests that the random method overestimated model Residual Prediction Deviation (RPD). Use of systematically selected validation sets produced acceptable (RPDs ≥ 1.4) models for soil organic C (SOC), total N (TN), and exchangeable Ca and Mg using whole NIR spectra. Use of spectral refinement techniques improved MIR‐based models for SOC, TN, and exchangeable Ca to RPDs ≥ 1.4. Poor performance of models predicting other SQ indicators, including particulate organic matter (POM), potentially mineralizable N (PMN), and fluorescein diacetate hydrolysis (FDA), is attributed to the influence of mineralogy associated with different types of loess. Use of lithology‐based libraries may support reusable and affordable NIR‐based models to predict SOC, TN, Ca and Mg. The addition of weather or moisture co‐variates may be needed to build models reliant on NDVI.