SOIL SCIENCEFPT 2093

Lecture Week 14:Soil Fertility Evaluation

En Mohd Fauzie JusohLecturer

Agrotechnology ProgrammeFaculty of Agro-Based Industry

Universiti Malaysia Kelantan (Jeli Campus) Locked Bag No.100, 17600 Jeli, Kelantan.

014-2903025/fauzie.j@umk.edu.my/

Introduction

Optimum plant health and productivity of a cropping system depends on an adequate supply of plant nutrients. The quantity of nutrients required by plants varies depending on:

• plant species and variety• yield potential• soil properties• environment • Management

Knowing the relationship between test results and crop nutrient response is essential for providing an accurate nutrient recommendation. Several techniques are commonly employed to assess the nutrient status of a soil:

• nutrient-deficiency symptoms of plants• tissue analysis of plants growing on the soil• remote sensing• soil analysis

Plant Nutrient-Deficiency Symptoms

Each visual symptom is related to a nutrient function in the plant.

Most nutrients have several functions, making it difficult to identify the reason for a particular deficiency symptom.

Understanding nutrient mobility in the plant is important to accurately identify a specific nutrient-deficiency symptom.

In addition to leaf symptoms, nutrient deficiencies have a marked effect on root growth.

Visual deficiency symptoms can be related to factors other than nutrient stress.

Plant Nutrient-Deficiency Symptoms

Plant Nutrient-Deficiency Symptoms

Nutrient-deficiency symptoms appear when nutrient supply is

so low that the plant cannot function properly.

Nutrient-deficiency symptoms appearing during early growth may disappear as the growing season progresses, or there may be no measurable yield benefit.

With cooler temperatures, nutrient uptake is reduced because:

• mass flow of nutrients is reduced by decreased growth rate and transpiration

• diffusion rate decreases with declining temperature and a lower concentration gradient

• Mineralization of organic bound nutrients is reduced

Plant Analysis

Plant analysis methods include tests on fresh tissue in the field and analyses performed in a laboratory. Plant analyses are performed to:

• verify the accuracy of an assessment of visual deficiency symptoms

• identify plant nutrient shortages before they appear as symptoms• help in determining the relative nutrient-supplying capacity of the

soil• quantify the effect of nutrient addition on nutrient concentration

in the plant• study the relationship between plant nutrient status and crop

performance (i.e., yield)

Plant Analysis

• Tissue TestsNutrient analysis on fresh tissue is important in

diagnosing nutrient needs of growing plants.

Application of nutrients to correct a nutrient stress

identified with a tissue test may not be feasible

because:• the deficiency may have already caused yield loss

• the crop may not respond to the applied nutrient at the specific growth stage tested

• the crop may be too large to apply nutrients

• climatic conditions may be unfavorable for fertilization

Plant Analysis

• Tissue Tests (cont.)

Cell Sap TestsSemiquantitative estimates of plant N, P, and K can be rapidly obtained

with simple plant tissue tests conducted in the field. Plant leaves or stems are chopped up and extracted with reagents specific for each nutrient. Plant tissue can also be squeezed with a garlic press to transfer plant sap to filter paper and color-developing reagents are then added. The color intensity of the cell sap/reagent mix is compared with a standard chart that indicates very low, low, medium, or high nutrient content.

Plant Analysis

• Tissue Tests (cont.)Total Analysis

Total analysis is performed on specific plant parts (e.g., petioles,

stems, leaves) in a laboratory. After sampling, plant material is

dried, ground, and nutrient content determined following wet

digestion with concentrated acid or dry ashing in a high-

temperature oven. As in tissue tests, the plant part selected is

important, with the most recently matured leaf preferred.

Samples should be kept dry or refrigerated and protected from

contamination.

Plant Analysis

• Tissue Tests (cont.)Sampling Time

Growth stage is important in plant analysis because nutrient status and demand vary during the season. Nutrient concentrationin vegetative partsusually decreaseswith maturity.Misinterpretation ofplant analysis resultsare common ifsampling time is notidentified correctly.

Deficient

Adequate

CNR

Greenhouse and Field Tests

• Greenhouse TestsSimple greenhouse tests involve growing plants insmall amounts of soil collected from a field suspectedof being nutrient deficient to assess nutrient availability.

Field Tests

• Strip TestsNarrow field strips where selected nutrient treatments have been appliedcan help verify theaccuracy of nutrientrecommendations.The test resultsmust be interpretedwith caution if theyare unreplicated.Replication of striptests on severalfarms is alsohelpful.

Greenhouse and Field Tests

• Field TestsMeasuring crop response to applied nutrients is commonly done by agricultural scientists developing nutrient recommendations. After treatments are selected, they are randomly assigned to an area of land. The treatments are replicated to obtain more reliable results and to account for soil variations at the experimental site.

Soil Testing

• Objectives of Soil Tests

Soil test information can be used to: • provide an index of nutrient availability in soil. The soil test or extractant

is designed to extract a portion of the nutrient from the same “pool” (i.e., solution, exchange, organic, or mineral) used by the plant

• predict the probability of obtaining a profitable response to fertilizer or lime. Although a response to applied nutrients will not always be obtained on low-testing soils because of other limiting factors, the probability of a response is greater on low-testing soils.

• provide a basis for development of fertilizer and lime recommendations. The basis for nutrient recommendations relies on detailed laboratory, greenhouse, and field studies.

Soil Testing

• Objectives of Soil Tests (cont.)– The objective of soil testing is to simply help predict

the amount of nutrients needed to supplement native soil nutrient supply.

– The soil testing-nutrient recommendation system is comprised of four consecutive steps:

1. Collect a representative soil sample from the field.

2. Determine the quantity of plant available nutrient in the soil sample (soil test).

3. Interpret the soil test results (soil test calibration).

4. Estimate the quantity of nutrient required by the crop (nutrient recommendation).

Soil Testing

• Nutrient RecommendationsNutrient Mobility: Soil test interpretation for purposes of making

nutrient recommendations is influenced by the mobility of the nutrient.Mobile Nutrient Recommendations: With mobile nutrients, soil test buildup and/or maintenance programs are not viable, because these nutrients are readily mobile in the root zone in many soils.Immobile Nutrient Recommendations: With immobile nutrients, crop yield potential is limited by the quantity of nutrient available at the soil-root interface. Generally, solution concentrations of immobile nutrients are low, and replenishment occurs through exchange, mineralization, and mineral solubility reactions.

Questions… Thank You