Russell Yost

Application of geostatistics to spatial studies of soil properties

Publisher Summary This chapter reviews some of the traditional methods of describing soil variability, discusses geostatistical approaches to quantifying spatial dependence and their use for interpolation under different kinds of spatial variation, and identifies some future applications of geostatistics to spatial studies in soil and agronomic research. Recognition of the importance of spatial variability on land use has led to the study of soil heterogeneity, ranging from a global scale to changes in structural and chemical composition of soil minerals on a microscale. Soil classification and soil survey have traditionally been the most practical approaches to grouping similar and separating different soils on a regional scale. Variability of properties within soil mapping units and within smaller sampling units—such as fields, experimental plots, or pedons, is acknowledged and has been described by classical statistical methods. Developments in statistical theory enable spatial relationships among sample values to be quantified and used for interpolation of values at unsampled locations. These developments are based on the theory of regionalized variables. This theory takes into account both the structured and random characteristics of spatially distributed variables to provide quantitative tools for their description and optimal, unbiased estimation. Geostatistical analysis of spatial variability is applied to estimation of ore reserves in the mining industry, water resources research, soil science, and archaeology.

PARTITIONING SOIL PHOSPHORUS INTO THREE DISCRETE POOLS OF DIFFERING AVAILABILITY1

The Hedley phosphorus (P) fractionation procedure provides an alternative for characterizing soil P availability without qualifying the component P species. Interpretation of results involving all fractions is complicated and offers little practical utility. The objective of this study was to group

Uncertainty in a pesticide leaching assessment for Hawaii

Abstract In this paper we report the predictive uncertainty associated with using the retardation factor ( RF ) as an index to evaluate pesticide leaching in Hawaii soils when uncertainty exists within the soil and chemical data used to excite the RF model. Our analysis takes two separate but ultimately related tacks. First, we assess the uncertainty caused by extrapolating soil properties between taxonomic categories. Second, we characterize the amount of uncertainty for calculated RF values due to data uncertainty by using first-order uncertainty analysis. Our results indicate that the RF index should only be used with soil information from the lowest taxonomic category and that even then considerable uncertainty will exist in the predicted RF values used to screen and rank chemicals.

Impact of uncertainty in soil, climatic, and chemical information in a pesticide leaching assessment.

A simple mobility index, when combined with a geographic information system, can be used to generate rating maps which indicate qualitatively the potential for various organic chemicals to leach to groundwater. In this paper we investigate the magnitude of uncertainty associated with pesticide mobility estimates as a result of data uncertainties. Our example is for the Pearl Harbor Basin, Oahu, Hawaii. The two pesticides included in our analysis are atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and diuron [3-(3,4-dichlorophenyul)-1,1-dimethylarea]. The mobility index used here is known as the Attenuation Factor (AF); it requires soil, hydrogeologic, climatic and chemical information as input data. We employ first-order uncertainty analysis to characterize the uncertainty in estimates of AF resulting from uncertainties in the various input data. Soils in the Pearl Harbor Basin are delineated at the order taxonomic category for this study. Our results show that there can be a significant amount of uncertainty in estimates of pesticide mobility for the Pearl Harbor Basin. This information needs to be considered if future decisions concerning chemical regulation are to be based on estimates of pesticide mobility determined from simple indices.

The reduction in zinc concentration of wheat grain upon increased phosphorus-fertilization and its mitigation by foliar zinc application

Background and aimsMalnutrition resulting from zinc (Zn) and iron (Fe) deficiency has become a global issue. Excessive phosphorus (P) application may aggravate this issue due to the interactions of P and micronutrients in soil crop. Crop grain micronutrients associated with P applications and the increase of grain Zn by Zn fertilization were field-evaluated.MethodsA field experiment with wheat was conducted to quantify the effect of P applications on grain micronutrient quality during two cropping seasons. The effect of foliar Zn applications on grain Zn quality with varied P applications was tested in 2011.ResultsPhosphorus applications decreased grain Zn concentration by 17–56%, while grain levels of Fe, manganese (Mn) and copper (Cu) either remained the same or increased. Although P applications increased grain yield, they restricted the accumulation of shoot Zn, but enhanced the accumulation of shoot Fe, Cu and especially Mn. In 2011, foliar Zn application restored the grain Zn to levels occurring without P and Zn application, and consequently reduced the grain P/Zn molar ratio by 19–53% than that without Zn application.ConclusionsFoliar Zn application may be needed to achieve both favorable yield and grain Zn quality of wheat in production areas where soil P is building up.

Using Segmented Regression Models to Fit Soil Nutrient and Soybean Grain Yield Changes due to Liming

Frequently soil-plant relationships and responses are complex combinations of increases-level-decreases consisting of linear segments of differing slope. Segmented regression is very useful to express and quantify such relationships and responses. Fitting segmented regression models to such data, however, remains a challenge. The problem is in estimating the join points and coefficients. We use median functions to express segmented regression models, and estimate the join points by standard estimation routines such as Marquardt, Newton, and doesn’t use derivatives (DUD) methods that are available in statistical software such as SAS. Segmented straight-line models are fit to data reflecting soil Manganese (Mn), Calcium (Ca), Phosphorus (P), and soybean yield changes under different soil pH conditions due to liming. A systematic comparison of the slopes and join points suggests that different mechanisms are limiting soybean yield at different intervals as soil pH increased.

A survey of soil fertility status of four agroecological zones of mozambique

Mozambique includes 10 agroecological zones with distinct climate and cropping systems (INIA, 1980). Agricultural production is more intensively practiced in the central and northern parts of the country where agroecological conditions are favorable. As a result of 16 years of civil war and low funding for agricultural research few assessments of soil nutrient status have been possible. To assess soil nutrient status, four agriculturally promising agroecological zones were selected for a survey. Sixty-two sites were sampled, and composite samples of surface and subsurface soils were taken and analyzed for properties considered critical for the production of food crops. The sample points were recorded with a differential global position system and mapped. The results indicate that most of the soils are low in effective cation exchange capacity, moderate in organic matter, moderate to strongly acidic, moderately weathered, and moderate to high in P sorption capacity. In general, these soils can be classified as having low to moderate fertility. Findings of this study indicate limitations of the existing map of soil resources of Mozambique. The results of this study suggest that additional sampling and soil survey will be required to improve the quality of soil surveys for site-specific applications. A site-specific soil survey is recommended that would provide additional information on soil resources and would greatly improve the current soil map that has an inadequate soil database. Furthermore, calibration and correlation studies are recommended for better decisions on soil nutrient management for ensuring food security.

Growth potential of twelve Acacia species on acid soils in Hawaii

Abstract Reforestation of degraded tropical sites is often hampered by soils of high acidity, high aluminum saturation, and low fertility. To evaluate the possibility of cultivating Acacia species on such soils, a study was conducted at Waiawa, HI, to test growth under conditions of (1) high acidity (primarily aluminum) and nutrient stress, and (2) no acidity stress and high nutrient availability. Twelve Acacia species, including the important native Hawaiian species Acacia koa , were established on a Ustic Kanhaplohumult soil. The experimental design was a split plot with two fertility treatments as the main plots and the 12 Acacia species as subplots. The treatments were: low fertility (F 0 ; 143 kg ha -1 14–14–14 plus micronutrients) and high fertility (F 1 ; 8 Mg ha -1 lime, 143 kg ha -1 14–14–14 plus micronutrients, 200 kg P ha -1 , and 77 kg K ha -1 ). Acacia angustissima , Acacia aulacocarpa , Acacia auriculiformis , Acacia cincinnata , Acacia crassicarpa , Acacia implexa , Acacia koa , and Acacia mangium grew significantly faster under the high fertility treatment. Three species, A. cincinnata , A. crassicarpa , and A. mangium , are recommended for planting on infertile acid soils. The volume of A. koa was increased ten-fold by the high fertility treatment. Additional study on koas nutritional requirements is suggested in order to identify the nutrients contributing to this increased growth.

P nutrition of cassava, including mycorrhizal effects on P, K, S, Zn and Ca uptake

Abstract The nutritional requirements of cassava are ill-defined. This paper deals with the P requirements of cassava and the effect of P on other nutrients both in the presence of VA mycorrhizae and in soils when VA mycorrhizae were eliminated by fumigation. Cassava was grown on field plots with ten levels of phosphorus (0.002-1.6 ppm P in solution) on two Oxisols in Hawaii. Six cultivars were compared at one location. At the other location the significance of vesicular-arbuscular (VA) mycorrhizae on the nutrition of cassava was investigated. There was a substantial increase in vegetative growth with increased P fertilization in the cultivar experiment; however, root yields were not greatly affected. Even at very low extractable soil P levels (Bray-1 P, 1 ppm) five out of the six cultivars did not respond to P fertilization. One cultivar, Ceiba, produced 42–48 t/ha of roots when P in solution was in the range 0.003-0.025 ppm. In the second experiment the role of VA mycorrhizae was studied by fumigating one half of each plot with methyl bromide which destroyed VA mycorrhizal fungi. Plants grown on the fumigated plots did not become infected with VA mycorrhizae during the first 80 days of the growing period. Cassava, cultivar Ceiba, was grown along with six other species. One of these was chinese cabbage which does not form mycorrhizal associations. Leaves from non-mycorrhizal cassava plants (fumigated plots) invariably contained less P on a percentage basis than leaves from mycorrhizal plants (non-fumigated plots). On the low P plot, leaf P decreased from 0.30 to 0.11% when VA mycorrhiza formation was precluded by fumigation. Likewise K and S concentrations in leaves decreased by 30% and Zn by 10%. There was no evidence that mycorrhizae promoted Ca uptake. These observations provide a basis for explaining why the P requirements of cassava in nutrient solution culture are very great, whereas cassava is generally unresponsive to P fertilization in the field.

Fertilization response and nutrient diagnosis in peach palm (Bactris gasipaes): a review

Peach palm (Bactris gasipaes Kunth) is a relatively new food crop with great potential for the humid tropics. Native to tropical America, it is commercially grown to produce hearts-of-palm and, to a lesser extent, an edible fruit. Peach palm is well adapted to nutrient poor, acid soils, and is cultivated in Brazil and Costa Rica on highly weathered soils with low pH, high aluminum saturation and, often, low organic matter content. Fertilization trials on peach palm have shown significant responses to applied nitrogen while the response to other nutrients such as phosphorus has been less frequent. Additional research, however, is necessary to determine soil and foliar nutrient critical levels and to address questions concerning peach palm growth responses to nutrient additions varying in time and space. Recycled nutrients likely contribute significantly to peach palm nutrition because plant residues are produced in considerable amounts and can decompose rapidly in commercial peach palm plantation in humid environments where cut leaves and stems are left in the field following harvest. On the other hand, nutrient exports from the system are relatively small (e.g., 4.8–6.4 kg P ha-1yr-1, 28–32.3 kg N ha-1 yr-1, 31–45.2 kg K ha-1 yr-1). As for most perennial tree crops, diagnosis of nutrient deficiencies in peach palm is less clear than in annual crops because of factors such as nutrient cycling, internal retranslocation, stand age, foliage age and position within the crown, and seasonal and climatic variations. Some studies on peach palm have examined variation in nutrient content within leaves and plants, and among plants as well, but the sensitivity of different plant tissues to reflect changes in nutrient uptake and response to nutrient additions should be investigated in controlled field experiments.