Soil Fertilizer Recommendations Research Articles

Boundary line analysis and machine learning models to identify critical soil values for major crops in Guatemala

AbstractAccurate and economically sound soil fertility recommendations are critical for ensuring profitable food production for smallholder farmers. However, such recommendations are lacking in many areas due to insufficient soil and crop response data. This study was conducted between 2016 and 2022 using boundary line analysis to evaluate crop response to soil fertility on 644 farms in Guatemala. We identify optimal soil property conditions for maize (Zea mays L.), common bean (Phaseolus vulgaris L.), and coffee (Coffea arabica L.) production in Guatemala and use crop price information to develop economically sound fertilization recommendations. We also analyzed the drivers of yield outcomes and assessed their relative importance with machine learning (ML) models. Results demonstrate that a majority of country‐level data currently have sub‐optimal soil nutrient levels and by optimizing nutrients, yields and profits could be improved in 64%, 51%, and 69% of maize, common bean, and coffee crops, respectively. In addition, ML underscored the central role of climate in shaping yield outcomes. Variable importance rankings from random forest indicated climate and water balance variables increased predictive accuracy more than soil parameters, highlighting the critical need for climate‐smart adaptations in the region. The pairing of boundary line with ML analysis provided unique and complementary information about factors that drive yield of major crops in Guatemala. This is an effective approach for developing fertility recommendations in Guatemala and could be replicated in other countries where critical nutrient recommendations are currently lacking for closing yield gaps and identifying yield response to climatic stochasticity.

On‐farm corn phosphorus response reveals importance of soil testing

Core Ideas Increased soil test P values above the critical threshold reduces the likelihood of grain yield response to P fertilizer application. Soil test P critical concentrations of 14 ppm indicated no change from Tri‐State Soil Fertility recommendations. Shallower soil sampling (0–2 inches) did not improve relationship between soil test P concentration and relative grain yield.

Soil balancing within organic farming: negotiating meanings and boundaries in an alternative agricultural community of practice

Soil balancing is widely used in organic farming, but little is known about the practice because technical knowledge and goals for the practice are produced and negotiated within an alternative community of practice (CoP). We used a review of the private soil balancing literature and semi-structured interviews with farmers and consultants to document the knowledge, shared meanings, and goals of key actors within the soil balancing CoP. Our findings suggest this CoP is dominated by discourse between private consultants and farmers, with few contributions to or from scientists or the peer reviewed literature. The idea of soil balancing is centered around improving soil quality through adjustments in Base Cation Saturation Ratios (BCSR), and practitioners report a wide range of positive agronomic outcomes. For most soil balancers, however, BCSR is only one part of a broader approach to soil health management that also utilizes traditional soil fertility recommendations and soil health-building cultural management practices. Meanwhile, a survey of land grant university soil fertility specialists and the peer-reviewed literature documented a high degree of skepticism and a lack of scientific evidence that BCSR can boost crop yields. We conclude that this scientific discourse reflects a disconnect from the practices and meanings used in the soil balancing CoP. While tensions between the dominant and niche agricultural knowledge systems are not unique, we believe a better appreciation for the nuanced meanings and goals within the soil balancing CoP present an opening for expanded collaborations with scientists doing research on soil health.

Foliar Elemental Analysis of Brazilian Crops via Portable X-ray Fluorescence Spectrometry.

Foliar analysis is very important for the nutritional management of crops and as a supplemental parameter for soil fertilizer recommendation. The elemental composition of plants is traditionally obtained by laboratory-based methods after acid digestion of ground and sieved leaf samples. This analysis is time-consuming and generates toxic waste. By comparison, portable X-ray fluorescence (pXRF) spectrometry is a promising technology for rapid characterization of plants, eliminating such constraints. This worked aimed to assess the pXRF performance for elemental quantification of leaf samples from important Brazilian crops. For that, 614 samples from 28 plant species were collected across different regions of Brazil. Ground and sieved samples were analyzed after acid digestion (AD), followed by quantification via inductively coupled plasma optical emission spectroscopy (ICP-OES) to determine the concentration of macronutrients (P, K, Ca, Mg, and S) and micronutrients (Fe, Zn, Mn, and Cu). The same plant nutrients were directly analyzed on ground leaf samples via pXRF. Four certified reference materials (CRMs) for plants were used for quality assurance control. Except for Mg, a very strong correlation was observed between pXRF and AD for all plant-nutrients and crops. The relationship between methods was nutrient- and crop-dependent. In particular, eucalyptus displayed optimal correlations for all elements, except for Mg. Opposite to eucalyptus, sugarcane showed the worst correlations for all the evaluated elements, except for S, which had a very strong correlation coefficient. Results demonstrate that for many crops, pXRF can reasonably quantify the concentration of macro- and micronutrients on ground and sieved leaf samples. Undoubtedly, this will contribute to enhance crop management strategies concomitant with increasing food quality and food security.

Soil and crop response to phosphorus and potassium management under conservation tillage

AbstractIn conservation tillage systems, proper fertilizer phosphorus (P) and potassium (K) management is critical to optimize yield and minimize negative environmental impacts. The objective of this study was to assess the responses of crop yield, nutrient use efficiencies, root growth, and soil test P and K levels to tillage, fertilizer placement, and fertilizer rates in a corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] rotation. Experiments were conducted for 8 yr in Illinois with tillage/fertilizer placement as the main plot (no‐till/broadcast [NTBC], strip‐till/broadcast [STBC], and strip‐till/deep band [STDB]) and PK fertilizer rates as the subplot. The NTBC treatment consistently reduced yields in corn by 6.2 and 4.5% and in soybean by 3.1 and 6.1% relative to STBC and STDB, respectively. Also, NTBC had greater root length density at in‐row and between‐row positions relative to STBC and STDB. Nutrient use efficiency indices (partial nutrient balance, agronomic efficiency, and partial factor productivity) declined with increasing P and K rates but were not affected by tillage/fertilizer placement treatments. Deep banding significantly reduced soil P and K concentrations in surface layers while increasing them at the depth of application. These results underscore the reported potential for deep banding combined with strip‐till to improve conditions for nutrient uptake while reducing the risk for nutrient losses to the environment. Critical soil test P and K levels (21 mg P kg−1 and 217 mg K kg−1) were similar for P and greater for K than the current university recommendations, which highlights the need for continuous refinement of soil fertility recommendations to keep pace with changes in production technologies and yield levels.

English

With slash-and-burn agriculture, changes in soil properties occur, which could influence crop production and future soil fertility recommendations. The objectives of this study were to: Identify dynamic soil properties that could be used to monitor soil quality; evaluate residual effects of slash-and-burn; and establish P and K fertilizer equivalence values of ash from slash-and-burn. Each experimental site was divided into 3 blocks within which treatments were randomly allocated. Broadcast burning and pile burning were carried out as practiced by local farmers. Soil samples were collected before burning (control), immediately after burning (burned) and one year after burning and cropping (burned-cropped), hereafter referred to as treatments. Soil samples were analyzed following standard analytical methods. P and K fertilizer equivalence values of the soil tests immediately before burning and after one year cropping of burned land were established and compared. The most sensitive soil properties to slash-and-burn were coarse silt, fine silt, pH, organic carbon (OC), total N (totN), P, Ca, Mg, K, Na, exchange acidity, effective cation exchange capacity (ECEC) and base saturation (BS). Between 47 and 87% of increases in content of exchangeable bases and available P resulting from burning of forest vegetation cover is lost after one year of cropping positive. Benefits in soil P and K attributed to slash and burn agriculture after one year cropping in terms of fertilizer equivalence was between 1 to 18 kg P2O5 and 22 to 76 K2O. P and K fertilizer recommendations for targeted crop yields based on the initial soil fertility status of the secondary forest in the humid forest zone of Cameroon should be 9 kg P2O5 and 49 kg K2O less in the second year of cropping.   Key words: Slash-and-burn, soil properties, humid forest zone, shifting cultivation, Southern-Cameroon.

Soil Heterogeneity and Soil Fertility Gradients in Smallholder Farms of the East African Highlands

Heterogeneity in soil fertility in these smallholder systems is caused by both inherent soil-landscape and human-induced variability across farms differing in resources and practices. Interventions to address the problem of poor soil fertility in Africa must be designed to target such diversity and spatially heterogeneity. Data on soil management and soil fertility from six districts in Kenya and Uganda were gathered to understand the determinants of soil heterogeneity within farms. Analysis of the variance of soil fertility indicators across 250 randomly selected farms (i.e., 2607 fields), using a mixed model that considered site, sampling frame, farm type, and field as random terms, revealed that the variation in soil organic C (6.5–27.7 g kg−1), total N (0.6–3.0 g kg−1), and available P (0.9–27 mg kg−1) was mostly related to differences in the inherent properties of the soils across sites (50 to 60% of total variance). Exchangeable K+ (0.1–1.1 cmol(+) kg−1), Ca2+ (1.5–14.5 cmol(+) kg−1), Mg2+ (0.6–3.7 cmol(+) kg−1), and pH (5.1–6.9) exhibited larger residual variability associated with field-to-field differences within farms (30 to 50%). Soil fertility indicators decreased significantly with increasing distance from the homesteads. When this variable was included in the model, the unexplained residual variances—associated with soil heterogeneity within farms—were 38% for soil C; 32% for total N; 49% for available P; 56, 49, and 38% for exchangeable K+, Ca2+ and Mg2+, respectively; and 49% for the pH. In allocating nutrient resources, farmers prioritized fields they perceived as most fertile, reinforcing soil heterogeneity. Categorization of fields within a farm with respect to distance from the homestead, and soil fertility classes as perceived by farmers, were identified as entry points to target soil fertility recommendations to easily recognizable, distinct entities.

Changes in Soil Organic Carbon and Nitrogen Fractions with Duration of No‐Tillage Management

The influence of no-tillage (NT) management on labile soil N is poorly defined. To quantify changes in soil C and N fractions with duration of NT, we sampled Kempsville sandy loam (fine-loamy, siliceous, subactive, thermic Typic Hapludults) soils in the Coastal Plain of Virginia from farm fields that had similar cropping histories and nutrient management but varied in amount of time in continuous NT from 0 to 11 yr. At the 0- to 2.5-cm soil depth, there was a linear increase with time in NT for total organic C, total organic N, particulate organic matter (POM)-C, POM-N, POM-C/total organic C, POM-N/total organic N, hydrolyzable unidentified-nitrogen (hUN-N) and NH4–N (hNH4–N), and various biochemical classes of pyrolysate compounds determined by pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). At the 2.5- to 7.5-cm soil depth, there was a linear increase with time in NT for total organic C and N, hUN-N, hNH4–N, hydrolyzable α amino acid-nitrogen (AA-N) and amino sugar-nitrogen (AS-N) only; these rates of increase were lower than at the 0- to 2.5-cm depth. No measured C and N fractions increased at the 7.5- to 15-cm soil depth but POM-C/total organic C and POM-N/total organic N declined (p ≤ 0.10) at this depth, suggesting that the recalcitrance of C and N fractions increased at 7.5- to 15-cm in 11 yr. These patterns indicate that a new equilibrium level for these C and N fractions had not been reached but that their stratification of C and N pools with soil depth increased during 11 yr in NT. At the 0- to 2.5-cm depth, the labile N fractions, AA-N and AS-N approached or reached new equilibrium levels within 11 yr. Since these fractions are derived from soil microbial and plant biomass, the initial rapid increase in these fractions likely reflects an increase in N immobilization in the short term (3–6 yr) following adoption of NT. After this initial transition period, levels of AA-N and AS-N approach new elevated equilibrium levels, which would be reflected in a higher net N mineralization rate than under the previous tilled system. These results indicate that absolute values for labile soil N fractions such as AA-N and AS-N may not be readily interpretable with respect to soil fertility recommendations without considering whether these values are changing over time or are at an equilibrium level. Different patterns of change in POM-N vs. AA-N and AS-N indicate that these labile N fractions are distinct and may provide different types of information with respect to quantifying changes in soil fertility with time under NT.

Insuficiência do conceito mineralista para expressar a fertilidade do solo percebida pelas plantas cultivadas no sistema plantio direto

Fertilidade do solo é a capacidade deste de fornecer nutrientes, em quantidade e proporção adequadas para o desenvolvimento e produtividade das plantas, na ausência de elementos tóxicos. Este conceito, oriundo da teoria mineralista, é amplamente utilizado no mundo. Com a mudança do sistema de cultivo do solo do convencional (SC) para o plantio direto (SPD), é freqüente a obtenção de alta produtividade das culturas no SPD com valores de indicadores da fertilidade considerados inadequados para o crescimento e desenvolvimento das plantas no SC. É possível que a avaliação tradicional e, conseqüentemente, esse conceito não sejam adequados e, ou, suficientes, para expressar a fertilidade percebida pelas plantas em solos cultivados há longo tempo no SPD. Neste trabalho, objetivou-se avaliar a capacidade do conceito mineralista, e de sua avaliação, em expressar a fertilidade percebida por plantas de milho (Zea mays) em solo cultivado por longo período de tempo no SPD com diferentes rotações de culturas. As avaliações, por indicadores da fertilidade do solo e por rendimento de grãos, foram feitas na safra de verão 2005/2006, em dois experimentos irrigados, conduzidos há mais de 20 anos em Eldorado do Sul, RS, com diferentes históricos de cultivo. Os resultados evidenciaram que nem sempre os indicadores químicos da fertilidade do solo detectam a mudança na capacidade produtiva do solo promovida pelos diferentes sistemas de cultivo e rotações de culturas. Esses indicadores tiveram, em geral, baixo grau de associação com o rendimento das plantas. A avaliação e, conseqüentemente, o conceito mineralista da fertilidade, utilizado para definir a capacidade de um solo produzir abundantemente, foram insuficientes para expressar a fertilidade percebida pela cultura de milho em solos cultivados há longo tempo no SPD.

A Survey of Fertility Practices, Soil Fertility Status, and Tree Nutrient Status on Eastern North Carolina Christmas Tree Farms

“Choose and cut” Christmas tree production is gaining popularity in North Carolina, as well as the Southeastern United States. There are few recommendations concerning the fertility of Christmas trees except for the large Fraser fir (Abies fraseri) industry in the Appalachian mountain region. Outside of the mountains, Virginia pine (Pinus virginiana), eastern white pine (Pinus strobus), red cedar (Juniperus virginiana), and Leyland cypress (X Cupressocyparis leylandii) are commonly grown as “choose and cut” trees. This study was conducted in the piedmont and coastal plain of North Carolina with the objectives to determine (1) the fertility practices currently being used and (2) the current soil and tissue nutrient status of “choose and cut” Christmas tree fields. A mail survey was used to accomplish the first objective. Twenty farms, selected from survey respondents, were sampled to determine current soil and tissue nutrient status. Soil samples were taken at three depths to 45 cm. Survey data indicated that a wide variety of fertilization materials and practices were being used. Spring applications were somewhat common, but actual time of application varied. Tissue and soil levels of nutrients also varied. There was a poor relationship between soil test nutrient levels and tissue nutrient levels, indicating the need for routine tissue analysis. This study indicated the need for future research and extension programs focusing on eastern Christmas tree fertility. In particular, the survey indicated that Leyland cypress, for which no specific soil fertility recommendations exist, is grown widely enough to merit recommendation development.

Collecting Representative Soil Samples for N and P Fertilizer Recommendations

Soil fertilizer recommendations in modern crop production rely on laboratory analysis of representative soil samples. Regardless on how soil samples are collected (grid points, management zones, or whole fields) the accuracy and precision of the fertilizer recommendation can be improved by considering the factors influencing nutrient variability. As producer’s crop enterprise varies, it is recommended that producers select approaches that are suited for their operation. The objectives of this guide are to discuss how management influences nutrient variability and to provide insight into designing soil sampling protocols that provide accurate and precise fertilizer recommendations.

Traditional Rainfed Barley Production in the Andean Highlands of Ecuador: Soil Nutrient Limitations and Other Constraints

The soils of a barley producing area in the Andean highlands of Tungurahua province in Ecuador were investigated for their nitrogen (N) and phosphorus (P) supplying power. Phosphorus was found to be more limiting to barley production than N, possibly because crop rotations included legumes and additions of livestock manures which maintained adequate N levels in these high organic matter soils. A series of field studies were established in farmers' fields to assess the predictive capability of soil tests for barley yield response to added fertilizer N and P. Of the methods evaluated at six locations, a mineralization incubation for N and soil solution P were best correlated with the relative yield increase to applied nutrients. The estimated critical N mineralization level was 9 mg kg-1 day-1 to achieve a barley yield that was 80 to 90% of the potential yield at each site when both N and P supply were sufficient. The critical P concentration in soil solution was estimated to be 0.03 mg L-1. A multiple regression equation including soil test N and P levels accounted for 81% of the variation in yield across nine experimental sites. Although further studies that include several cropping seasons and more sites will be required to establish soil fertility recommendations, the results from this study indicate the potential for predicting the severity of nutrient limitations on these Andean highland soils.

LABORATORY DETERMINATION OF FIELD BULK DENSITY FOR IMPROVING FERTILIZER RECOMMENDATIONS OF ORGANIC SOILS

The objectives of this study were to find ways to improve the accuracy of soil fertilizer recommendations by taking into account the variation in bulk density (BD) of organic soils. To achieve this end, field BD values of 30 organic soils (0.100–0.504 g/mL) were used to evaluate methods of measuring the BD in the laboratory by means of correlation and regression techniques. A simple and rapid procedure using the reconstituted BD of field-moist soils was the most accurate means of determining the average field BD in the laboratory, as indicated by the correlation coefficient obtained between the BD values obtained by this method and those in the field (r = 0.975**). The second most accurate method relied upon the exponential relationship between the water content of soils and their BD (R2 = 91.1 %). The least exact method of correcting for BD variations was to scoop a volume of dried (65 °C) and sieved (2-mm) soils, as is done in some soil test laboratories. Although the values obtained by this method were related (r = 0.502**) to the field data, drying caused shrinkage of soils, thereby increasing their BD about twofold. Soil pH (r = 0.716**) and percentage ash contents (r = 0.851**) were also related to the field BD of soils. These tests could be used to estimate the BD of soils when the preferred method cannot be used. Regression equations are provided for relating appropriate test values to the BD of organic soils.

Soil fertility recommendations based on a balanced saturation of the cation exchange capacity

Abstract The method for making lime and fertilizer recommendations based on a soil test are presented. These procedures are used by United States Testing Company.