MSc

The current work, entitled "Evaluation of STCR-based targeted yield equations of
Amaranthus (Amaranthus tricolor L.) in southern laterite soils (AEU-8) of Kerala," was
conducted in the Department of Soil Science and Agricultural Chemistry, College of
Agriculture, Vellayani from the period March 2022 to June 2022. In this work, a field
experiment based on randomized block design was carried out to test and validate the targeted
yield equation produced by STCR 2014 for the cultivation of Amaranthus at (AEU-8),
Instructional farm, College of Agriculture, Vellayani, Thiruvananthapuram.
The five treatments used in the experiment were the organic and conventional package
of practices based nutrient management as T1 and T2 and three levels of Soil test crop response
(STCR) based on targeted yield with T3, T4 and T 5 having nutrient management for a targeted
yield of 20, 22.5 and 25 t ha-1
. The following equation targeted yield equation used in the study
was developed by All India Co-ordinated Research Project on STCR at the College of
Horticulture, Kerala Agricultural University, Vellanikkara:
FN = 3.50T – 0.10SN – 0.19ON
FP2O5 = 1.44T – 2.58SP – 0.30OP
FK2O = 1.35T – 0.06SK – 0.13OK
Where, FN, SN and ON are fertilizer nitrogen dose which was added through fertilizer, soil
available nitrogen and nitrogen contribution of organic sources respectively. FP2O5, SP and OP
are fertilizer phosphorus dose which is added through fertilizer, soil available phosphorus and
phosphorous contribution of organic sources respectively. FK2O, SP and OP are fertilizer
potassium dose which is added through fertilizer, soil available potassium and potassium
contribution of organic sources respectively.
The nutritional status of organic manures used in the experiment and initial soil fertility
levels of the field were analysed to calculate the quantity of fertilizer dose in T3, T4 and T5.
Biometric observations, yield parameters, pre-and post-harvest physicochemical properties of
soil and the nutrient content in shoot, root, leaf and dry matter production were recorded to
study their effect on yield.
Among all the treatments T5 recorded the highest values for biometric observations and
yield parameters. The treatment T5 recorded a yield of 24.79 t ha-1
. Similarly, the dry matter
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production, number of leaves per plant and height of the plants were 55.33 g plant-1
, 36.86 and
42.17 cm respectively. The plant height and the number of branches per plant and the dry matter
production too were the highest for this treatment (T5).
The post-harvest analysis of soil physical properties such as particle density, bulk
density and porosity showed no significant difference among the treatments. However, a
significant difference was found in water holding capacity and was highest in T1. The treatment
T1 recorded the lowest level of macronutrients while the highest level was recorded in T5. All
the treatments resulted in an increase in the organic carbon content of the soil after the
experiment. Thus, treatments had negligible influence on overall soil health status as indicated
by an insignificant difference among the treatments with respect to dehydrogenase activity and
the microbial biomass carbon of the post-harvest soil samples.
The lowest uptake of macronutrients was observed in T1 which recorded the lowest
yield. The highest uptake of macronutrients was observed in T5 which recorded the highest
yield. This suggests that among the treatments higher levels of fertilizer application for the
targeted yield range of 20 to 25 t ha-1
have a direct influence on nitrogen, phosphorous and
potassium uptake and therefore an increase in crop production. There was a significant
difference between the treatments with respect to secondary and micronutrient content of soil
and plant respectively. These nutrients were maintained within a sufficiency range by
application of amendments and organic matter.
The biometric parameters and yield were positively correlated. Also, a positive
correlation was observed between yield parameters and yield. There was a positive correlation
for yield with the post-harvest soil nutrient status of nitrogen, phosphorus and potassium
respectively. The yield showed a significantly positive correlation with the nutrient content of
the leaf and shoot. Similarly, a positive correlation was observed between yield and plant
nitrogen, phosphorus and potassium uptake. The economics of cultivation indicate that
treatment T5 had the highest profit and benefit cost ratio compared to the other treatments.
It can be concluded that the Soil test crop response-integrated plant nutrient system
based targeted yield equation with organic manure management for cultivating Amaranthus
tricolor can be adopted and extended to agro ecological unit 8 of Trivandrum district of Kerala,
India with a yield target of 25 t ha-1
. Therefore, the present study confirmed the possibility of
optimizing of the yield of Amaranthus sustainably with nutrient management alone using
targeted yield equations.