Abstract
Cereal grains are the major food of mankind and key to increased food
supplies. To feed the increasing world's population we have to increase the
present level of cereal productions, especially in the dry areas and scarce
rainfall, limited water resources and soil moisture areas. This can be done by
judicious husbandry of the limited water resources or soil moisture with
appropriate plant density. Reduced water use and or plant density can save
irrigation water per unit area facilitating more area under irrigation which
may contribute towards increased cereal productions. The efficiency of water
consumption (Ee) and water use efficiency (WUE) may reveal a quantitative
skill of DMY and can serve as an important indicator of the overall crop
performance in relation to water consumption. The major objective of the
study was to investigate the performance of some cereal crops for the efficient
utilization of limited water resources and soil moisture for the increased
cereal productions. Experiments were conducted using winter (wheat and
barley), summer (upland rice) cereals, and weed infestations was investigated
using nitrogen and spacings in transplanted rice.
The dissertation consists of eight chapters. In chapter I, significance of
the study, experimentation, objectives; in chapter II review of the relevant
literatures, in chapter VII a general conclusions and recommendations, and
in chapter VIII literatures cited were mentioned. Chapter III to VI elucidated
the results and discussions on the crop performance as affected by soil
moisture availability from tillering to maturity, reductions of applied water
resources from flowering to maturity, effect of mulches under various soil
moisture availability from tillering to maturity, and weed infestations in
transplanted rice fields as affected by plant density and nitrogen levels.
The efficiency of water consumption (E) was investigated taking into
account the total ET in mm from tillering to maturity of wheat, barley and
three upland rice cultivars. Results on the soil moisture availability and plant
density from tillering to maturity revealed that water consumption decreased
with the reduced soil moisture conditions and plant density. The excess dry
conditions hampered root growth and resulted reduced water consumption and DMY, and increased E. which might be due to that water consumption
increasing rate was less than the dry matter production rate. Increased plant
density enhanced DMY and E but not proportionate to the plant density,
rather per plant productivity was reduced due to less share of soil moisture
per plant. Reductions of plant density saved water consumption by 17.33 %,
18.17 %, 16.22 % and 15.58 %, but this caused reductions of grain yields by
33.33 %, 20.51%, 34.25% and 35.54 %, respectively at pF 2.0, pF 3.0, pF 2.0 ~ 3.0,
and pF 2.0~ 3.0 (straw mulch ). Compared to the standard condition (pF 2.0 ~
3.0 + 6-plants/pot), reduction of plant density saved water consumption by
13.02 %, 16.22 %, 22.22 % and 22.27% but grain yield also reduced by 26.22 %,
38.40 %, 34.25% and 31.36 %, respectively at pF 2.0, pF 3.0, pF 2.0~ 3.0, and pF
2.0~3.0 (straw mulch ). The results lead to comment that under the excess
moisture conditions, unproductively water consumption increased and was
not much productive to produce dry matter. By reducing plant density, water
consumption by plants can be avoided and a considerable amount of
irrigation water can be saved.
Wheat grain yield mostly depends upon water use after anthesis.
Results on the performance of wheat as affected by water application rates as
ET-deficits and plant density from flowering to maturity revealed that
reduction of water application saved water but affected DMY, and from 60%
water reduction to 40 % was affected more. Reducing plant density from 6-
plants/pot to 3-plants/pot or 1-plant /pot, water consumption was reduced to
79% or 64 %. But this reduced grain yield to 94.4 % and 60.7% at 3-plants/pot
and 1-plant / pot, respectively. By the same water it is possible to irrigate 1.27
or 1.56 times the wheat area which might increase total grain productions. It
was reported that the grain yield of wheat mostly depends upon the water
consumption after anthesis and therefore, after flowering to maturity is
considered as an moisture sensitive growth stage of wheat. Restriction of
irrigation water after flowering by 80%, 60% and 40 %, reduced the wheat
grain yield to 89.1%, 83.9% and 62.3 %, respectively and total DMY to 88.0 %,
79.5 % and 62.9 %, respectively compared to the standard condition. By
reducing water application to 80 %, 60% and 40 % at 6-plants/pot, it is
possible to increase the irrigated area by 1.25, 1.67 or 2.50 times. This will eincrease wheat production by. 1.12, 1.40 and 1.56 times. Furthermore, under
such conditions, reducing plant density to 3-plants/pot, 1.19 ~ 1.91 times total
DMY can be obtained. With the application of 80%, 60% and 40% water with
3-plants/ pot, 1.08~ 1.22 times the grain DMY and 1.09 ~ 1.23 times the total
DMY can be harvested. Results suggested that sacrificing some grain yield at
the reduced water application rate or reduced plant density, more grain WUE
could be achieved and a considerable amount of precious irrigation water can
o be saved. This will facilitate more area under irrigation which ultimately
would increase the total production. Therefore, based on the availability of
yam at water resources, plant density should be decided to grow or maintain after
ekn flowering for higher wheat grain production.
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Results on the performance of wheat as affected by mulches under
various soil moisture availability from tillering to maturity revealed that
irrespective of soil moisture availability, 37 % and 18% water was conserved
by vinyl mulch and straw mulch, respectively. Quantitatively, vinyl mulch
conserved, @ 0.83, 0.57 and 1.03 mm /day at pF 1.8, pF 2.5 and pF 1.8~2.8,
respectively over the no mulch. The corresponding rates with straw mulch
were 0.41, 0.33 and 0.71 mm /day, respectively. Oxygen deficiency at pF 1.8
hampered root growth and resulted reduced DMY, vinyl mulch aggravated
the situation and appeared as detrimental for root development. Straw and
vinyl mulch increased grain Ee by 9.33 % and 12.95 %, and total Ee by 18.65%
and 27.38% at pF 1.8 and pF 2.5, respectively relative to the standard
condition. Excess moisture during upland crop growing was not always
conducive for better crop performance, rather it resulted in the wastage of the
scarce water resources or limited soil moisture. Therefore, instead of flatly use
of mulches for water conservation, the idea of choosing and applying mulch
materials considering soil moisture availability or the amount of applied
irrigation water might considerably contribute towards increased wheat or
barley production.
Nine species of weeds representing six families were found to grow
and infest the transplanted Aman rice field in Bangladesh. Weed densities
were prominent at wider spacings, decreased gradually with the increase of
the rice plant density. Weed infestations increased linearly with nitrogen. It was concluded that soil moisture control by water application as a
percent of water reductions yielded better results, than as pF. Increased water
consumption was always not much productive use of water, therefore, to
avoid the unproductive use of the precious limited irrigation water
resources, it was recommended to consider the WUE by the crops (s). While
cropping with the limited water resources or soil moisture availability, for
higher WUE, relatively drier conditions were recommended. However, the
extent of DMY that could be sacrificed should also be considered. Knowingthe stock or availability of the water resources or soil moisture availability,plant density should be decided to grow successfully. Otherwise, plants may
die before completion of it's life cycle and can not harvest, resulting complete
wastage of the precious water resources. Reducing plant density and applyingwater from the moisture sensitive growth stages, it is possible to save a
considerable amount of irrigation water.
Therefore, it was highly recommended that considering the availabilityof the stock of water resources or soil moisture, water application plan from
the moisture sensitive growth stages should be prepared so that a
considerable amount of irrigation water could be saved. With the saved
water, more crop area can be brought under irrigation. This will reduce the
dry matter production per unit area, but will considerably increase the total
production in an area. If the stock or soil moisture is known, then plantdensity could be decided and following the technique of WUE, the amount ofexpected dry matter production in an area could be estimated. Thus the total
cereal productions in the limited water resources area could be increased
considerably.
Depending upon the soil moisture availability, adjusting the amount
of irrigation water and plant density, and it is necessary to establish a sound
water resources management policy. To do this, the technique of WUE have proved to be an important tool. However, these conclusions were based on
the pot experiments and to get more practical and accurate guidelines, field experimental results are necessary.