TOPIC

EFFECT OF DEFICIT IRRIGATION ON SOIL PROPERTIES,

PHYSIOLOGY AND NUTRIENT ASSIMLATION OF SWEET

PEPPER (Capsicum annuum)

BY

TABITHA MENSAH

INTRODUCTION

Water supplies are limited worldwide (Postel, 1998) and there is an

urgent need to identify and adopt better irrigation management

strategies.

Low moisture in the soil may however lead to problems of reduced

growth rate, metabolic activities, development and yield of crops.

Low soil moisture could also result in total loss of a farmer’s whole

crop or make his crops vulnerable to both biotic and abiotic

complications (Ware and McCollum, 1975).

INTRODUCTION CONT’D

Deficit irrigation, is a practice of reducing the amount of water

supplied to a crop or reducing the frequency of water application.

It ensures optimum yield in times of drought or make proper use of

irrigation water to achieve the maximum potential yield in times and

areas of abundant and almost free water for irrigation

The application of less water reduces the leaching effects of

nutrients from the root-zone and agrochemicals and the groundwater

quality is preserved (Pandey et al., 2000)..

BENEFITS OF SWEET PEPPER

SWEET PEPPER

Beautification, taste, flavour

Vitamins(thiamine, carotene, B12)

Spices, sauce, pickles

Phytochemical properties

BOTANY OF SWEET PEPPER

S.N:

Soil:

Temp:

Rainfall:

PROBLEM STATEMENT

Relative abundance or scarcity of water as well as the lack of

irrigation knowledge leads to over irrigation or under irrigation.

This results in leaching of plant nutrients, saturation of soil to create

anaerobic conditions which can result in root damage, reduced root

respiration, and lime hydrolysis as well as denitrification of nitrate

fertilizers.

PROBLEM STATEMENT CONT’

Therefore, there is the need to consider measuring the amount of

water applied to crop like sweet pepper which has an extensive

shallow root system, and is susceptible to water logging.

Efficient use of water by irrigation is becoming increasingly

important. (Oweis, 2000).

Deficit irrigation (DI) has been used as a water saving irrigation

technique in horticultural production.

GENERAL OBJECTIVE

The general objective of the study was to examine the effect of

deficit irrigation on soil properties, physiology and nutrient

uptake of sweet pepper.

SPECIFIC OBJECTIVES

There specific objectives of the study were:

To assess the effect of deficit irrigation on the harvest index and dry

matter accumulation of sweet pepper .

To assess the effect of nitrogen, phosphorus, potassium uptake by

sweet pepper.

To access the effect of deficit irrigation on the root system

architecture of sweet pepper.

JUSTIFICATION

Several researches have been carried out on deficit irrigation with

resulting indicating 10-15% reduction of crop water requirement had

no significant effect on the yield.

The interest of the research was to investigate the effect of deficit

irrigation on important soil properties such as bulk density, particle

density, infiltration rate, soil salinity.

Finally the study would seek to examine the effect of deficit irrigation

on nutrient uptake and utilization by sweet pepper.

STUDY AREA

The study was conducted at the engineering field of the School of

Agriculture Teaching and Research Farm at University of Cape Coast.

AREA FEATURES

Annual temperature of 23.2-33.2 ºC with an annual mean of 27.6 ºc

Relative humidity is 81.3-84.4% (Owusu-Sekyere et al 2011).

The annual rainfall is between 650 and 1100 mm (Alhassan, 2009).

Soil: sandy clayey loam of the benya series classified by Asamoah

(1973)

Location : central region of Ghana

EXPERIMENTAL DESIGN

Completely Randomized Block Design (CRBD) with three (3)

treatments (T1-T3) and three (3) replications (R1- R3).

Each replication had 4 (four) plants. In this study, sweet pepper

plants were grown in containers and placed under a transparent rain

shelter.

Two blocks were used for the study (morning and evening block)

TREATMENTS

After determining the crop water requirement (CWR) for the day,

the plots were subjected to different amounts of water, the

following treatments were imposed: T1, 100% of CWR; T2, 90% of

CWR; T3, and 80% of CWR. These treatments were applied both

for the morning and evening blocks.

DETERMINATION OF CROP WATER

REQUIREMENT(ETc)

Crop evapotranspiration (ETc) was calculated as the product of

reference evapotranspiration (ETo) and the dual crop coefficient

(Kc). Thus;

ETc = ETo ( Kcb + Ke) ……………..(1)

Where;ETc - is the crop evapotranspiration(mm),ETo - the reference evapotranspiration (mm),Kcb - the basal crop coefficient Ke - the evaporation coefficient.

PLANTING OF SWEET PEPPER

Sweet pepper seeds were nursed on the …………. and the healthy

seedlings were transplanted into the container under the rain shed on

………….. All the 72 plants comprising the treatment combination

were given equal volume of water (………) for eight days to ensure

uniformity among the seedlings before the various treatments were

administered.

IRRIGATION OF CROPS

A three day irrigation interval was employed.

The volume of water applied to each treatment was obtained by the

computation of weight loss by each container with the plants of the

treatment.

Weight of plant pot was determined using CAMARY 150kg

capacity electronic scale with a graduation of 500g.

IRRIGATION CONT’D

Density (kg/m3) = weight (kg)/volume (m3)

Density x volume = weight

Since the density of water is 1kg/m3 then

Volume = weight

FIELD LAYOUT

DATA PARAMETERS

Data was collected on the following parameters Soil physical properties ; bulk density, particle density and

porosity

Soil chemical properties ; Nitrogen %, potassium and

phosphorus content

Vegetative parameters ; dry matter accumulation and harvest

index

DRY MATTER ACCUMULATION

Leaves from the top, middle and down part of data plants randomly

selected after harvest were taken.

Fresh weight of the leaves was taken by weighing with an

electronic balance.

Samples were oven-dried at 105 ºC to constant weight to determine

their total dry weight.

Total dry matter of plant was the sum of total vegetative dry weight

and total fresh weight of fruit per plant.

Dm= Total dry weight of sample ×100

Total fresh weight of sample

(Patel & Rajput, 2013)

HARVEST INDEX

Harvest index was calculated by dividing total dry weight of fruit by

total dry weight of plant.

BULK DENSITY

Bulk density of soil was determined using the method as described by

(McKenzie et al., 2004).

Representative soil samples were collected from both surface,

subsurface and bottom using a standard metal ring cylinder with a

known volume.

Samples were then transferred into a weighed beaker (W1).

Weight of both beaker and soil samples were measured using an

electronic balance.

BULK DENSITY CONT’D

The samples were then oven dried for 24hrs at 105oC.

Samples were weighed (W2) and used to determine the dry weight.

Bulk density was calculated using the following formula;

Bulk density (g/cm3) = ( ( ))/( 𝐷𝑟𝑦 𝑠𝑜𝑖𝑙 𝑤𝑒𝑖𝑔ℎ𝑡 𝑔 𝑆𝑜𝑖𝑙 𝑣𝑜𝑙𝑢𝑚𝑒( 3)) 𝑐𝑚

Dry soil weight (g) = W2 – W1

Soil volume (cm3) = 3.14 x r2 x ring height.

PARTICLE DENSITY

A 100ml graduated cylinder was weighed and its weight recorded.

The cylinder was then filled with a sieved oven dried soil sample

to the 25ml mark then compacted.

Additional soil sample was added and compacted until soil reached

the 70ml mark of the cylinder.

A spatula was then used to scoop soil sample from the cylinder to

the 50ml mark.

The cylinder containing soil sample was weighed and the weight

recorded.

PARTICLE DENSITY CONT’D

Soil was then transferred from the cylinder to a weighed beaker.

The cylinder was then filled with water to the 50ml mark to make

the initial volume of soil.

The soil in the beaker was gradually transferred into the cylinder

while stirring to remove all forms of air bubbles.

The sample was allowed to settle after which water suspension was

recorded.

PARTICLE DENSITY CONT’D

Particle density was calculated as follows;

Volume of soil solids = final volume of soil – initial water volume

(50ml)

Particle density = oven-dry soil weight / volume of soil solids

POROSITY

Porosity of each sample was calculated by finding the ratio of bulk

density to particle density and multiplying by 100 to give the %

solid space. 100 were then subtracted from the % solid space to

obtain the porosity for each sample.

% solid space = (bulk density / particle density) x 100

% porosity = 100 - (% solid space)

PERCENTAGE NITROGEN

Micro-Kjedahl method was used for nitrogen determination.

Steps involved in nitrogen determination are;

Digestion, Distillation and Titration

𝑁 (%) = ( − ) )𝑆 𝐵 𝑋 𝑆𝑂𝐿𝑈𝑇𝐼𝑂𝑁 𝑉𝑂𝐿𝑈𝑀𝐸

(100 )𝑋 𝐴𝐿𝐼𝐺𝑈𝑂𝑇 𝑋 𝑆𝐴𝑀𝑃𝐿𝐸𝑊𝐸𝐼𝐺𝐻𝑇

Where

S - sample titre value

B – Blank titre value

PHOSPHORUS DETERMINATION

Bray No 1 method (with Ascorbic Acid) was used.

About 1g of soil sample was weighed into 15ml centrifuge tube

and 100ml extraction solution was added was added.

The content was centrifuge for 10minutes and then filtered.

2ml of the aliquot of the extract was pipette into 25ml volumetric

flask from the stock solution. 100ml of 5µgP/ml was prepared.

A set of working standards of P containing 0.0, 0.1, 0.2, 0.4, 0.6,

0.8, and 1.0µgP was prepared from the stock solution of 5µgP/ml

From this point, all the standards were treated in the same way by

adding 10ml of distilled water to each flask and 4ml of ascorbic

acid. Colour was allowed to develop by allowing the solution to

stand for 15minutes. Their respective absorbance was determined

with spectrophotometer at 882nm.

POTASSIUM DETERMINATION

About 5g of soil sample was weighed and transferred into a 100ml

extraction bottle. 20ml ammonium acetate was added and the

content was stirred and allowed to stand overnight.

The suspension was transferred into a 100ml volumetric flask fitted

with funnel filter and filter paper. The soil was leached 4 times with

successive ammonium acetate while allowing the funnel to drain

between each addition.

POTASSIUM CONT’D

The process continued until 100ml of filtrate has been collected.

The mark was made-up with ammonium acetate. Aliquot of the

extract was used for the determination of potassium by flame

photometry.

STATISTICAL ANALYSIS

The various results obtained were subjected to the analysis of

variance (ANOVA) using Genstat statistical software.

Mean comparisons were done using least significance difference

test at a probability level of 5%.

RESULTS

DISCUSSIONS

SOIL PHYSIOCHEMICAL PROPERTIES

NITROGEN

The amount of water applied to a soil has a significant effect on the

nutrient uptake of a plant. From the results obtained, it can be

deduced that the T1 had the highest uptake of nitrogen however the

difference between T1 and T2 is not significant.

The results correlate with that of Vincenzo Candido et al., (2009)

who stated that, nitrogen absorption, partitioning and translocation

is affected by water availability.

PHOSPHORUS

Unlike nitrogen and potassium, the uptake of phosphorus is not

significantly affected by the availability of water. K. Nahar and R.

Gretzmacher, (2002) reported that, moisture stress did not influence

significantly the uptake of phosphorous.

Shapiro et al. (1956) pointed out that translocation of phosphorus

increases when there is improvement in aeration.

POTASSIUM

The decrease in uptake of potassium with increasing moisture stress

at the end of the study can be as a result of the fact that uptake of

potassium like nitrogen increases with increasing moisture

availability.

Adequate amount of water in the soil tend to enhance aeration and

this according to Cline and Erickson (1956), would improve

potassium and nitrogen uptake.

DRY MATTER ACCUMULATION

Dry matter production decreased with increasing water stress

condition. The interaction effect of water deficit and sweet pepper

was highly significant in dry matter production under various

treatments.

According to Busso et al (1997) during their work reported that,

water stress had a greater effect on the stems, leaves and peduncles

compared to roots.

ROOT STRUCTURE

Root water uptake increases with increasing moisture availability at

the root zone of crops and decrease with increasing rate of deficit.

. Results from Marouelli and Silva, (2007), confirmed that, the

occurrence of moderate water deficits during the vegetative stage

favours deeper rooting allowing the plants to draw water from the

deeper soil layers

CONCLUSION

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