PhD

Zinc is an essential mineral nutrient with exceptional biological significance in plant and animal nutrition. It is associated with several enzyme systems that regulate various metabolic activities in plants.

In Indian Scenario more than 45% of soils are Zn deficient. Majority of the Kerala soils also recorded a low content of available Zn. Proper understanding of micronutrient availability in soil and extent of their deficiencies is the pre-requisite for efficient management of micronutrient fertilizer to sustain crop productivity.

The response of Zn application varies widely from crop to crop and soil to soil. Maize crop was found to be responsive to Zn. Fodder crops respond to micronutrients by increasing the dry matter yields and by changing their quality as a feed for animal nutrition.

In this context the present study on the Dynamics of zinc in Typic Kandiustults with special reference to nutrition in fodder maize (Zea mays.L) was carried out to satisfy the objectives viz. understanding the release pattern of Zinc from Zinc sulphate with and without FYM under the laboratory conditions, to elucidate the role of Zn in the growth, yield and quality parameters of fodder maize. when applied to soil as well as foliar application. The selection of the index plant part for foliar diagnosis and fixing up of the critical nutrient level in that plant part was also included in the experiment.

The incubation study on the release pattern of Zn from zinc sulphate was conducted in complete randomized design with 10 treatments and three replications. The treatments are given below:

T1 Soil alone: T2 Soil + Zn @ 0 kg ha-1 + FYM @ 10 tha-1 :T3 Soil + Zn @ 5 kg ha-1 : T4 Soil + Zn @ 5 kg ha-1 + FYM @ 10 tha-1 : T5 Soil + Zn @ 10 kg ha-1: T6 Soil + Zn @ 10 kg ha-1 + FYM @ 10 tha-1 :T7 Soil + Zn @ 15 kg ha-1 :T8 Soil + Zn @ 15 kg ha-1 + FYM @ 10 tha-1 ;T9 Soil + Zn @ 20 kg ha-1 T10 Soil + Zn @ 20 kg ha-1 + FYM @ 10 tha-1

The soil samples were collected at an interval of 15 days for a period of 75 days and analyzed for available Zn by DTPA method.

The results of the incubation study showed that when Zn was applied at 5, 10, 15 kg ha-1, the availability was in the medium range during the period of incubation and it has exceed 2.4mg kg-1 on the 75th day of incubation only, when Zn was applied @ 20 kg ha-1.

Initial soil profile study and the initial analysis of the surface and subsurface soil samples of experimental site were also carried out.

The field study comprised of two experimental crops with fodder maize cv. African Tall, in the Instructional Farm, College of Agriculture, Vellayani in RBD with 10 treatments and 3 replications. The treatments are given below:

T1 : NPK @ 120:60:40 kg ha-1 ; T2 : NPK @ 120:60:40 kg ha-1 + FYM @ 10 t ha-1 (POP recommendation); T3 : POP + Zn 5 kg ha-1 as ZnSO4(Soil application); T4 : POP + Zn 10 kg ha-1 as ZnSO4(Soil application); T5 : POP + Zn 15 kg ha-1 as ZnSO4(Soil application); T6 : POP + Zn 10 kg ha-1 as ZnSO4(Soil application); T7 : POP + 0.25% Zn as ZnSO4(foliar application); T8 : POP + 0.5% Zn as ZnSO4 (foliar application); T9 : POP + 0.75% Zn as ZnSO4(foliar application); T10 : Control.

After each experimental crop, a residual crop was also raised without any fertilizers or manures to study the residual effect of applied zinc for the previous crop.

The yield data of the first experimental crop revealed that T4 (POP + Zn 10 kg ha-1 as ZnSO4 as soil application), recorded the highest yield of 512 q ha-1. The higher dry fodder yield (103.92 q ha-1) per day green fodder yield (8.54 q ha-1) and leaf stem ratio (2.63) were also higher for the above treatment. The quality attributes viz. crude protein (10.93 per cent), crude protein yield were also showed for this treatment. For the first residual crop, T5 (POP + Zn 15 kg ha-1) recorded the maximum yield. In the second experimental crop, the T5 showed the maximum yield (519.3 q ha-1). For the second residual crop, T6 (POP + Zn 20 kg ha-1 as ZnSO4) of soil applied Zn gave the maximum yield.

The yield data of the first and second experimental crops were pooled and analyzed statistically. The pooled analysis data for the yield was found significant among treatments. For the pooled data, the T5 (POP + Zn 15 kg ha-1) with a mean yield of 468.8 q ha-1showed the highest yield and it was on par with T4, T8 and T9 which recorded and yield of 464.5 q ha-1 , 403.90 q ha-1, 418.30 q ha-1respectively. It is seen that the yield difference between T4 and T5 was only 4.3 q ha-1. For raising a single crop of fodder maize (African Tall), soil application of zinc sulphate @ Zn 10 kg ha-1 along with 120:60:40 NPK kg ha-1 + FYM 10 t ha-1 is recommended. Foliar spray of zinc sulphate @ 0.75% Zn at the 4th leaf stage recorded the highest yield among foliar application treatments and it was on par with T4.

Application of Zn @ 15 kg ha-1as soil application along with 120:60:40 NPK kg ha-1 + FYM 10 t ha-1 for the first crop of fodder maize will help to skip the Zn application for the succeeding crop.

From the studies on foliar diagnosis to identify the index plant part of this crop, 3rd leaf lamina from the tip at 25 DAS was selected as the index plant part. The critical nutrient level of Zn for maximum response to yield in plant was standardized using the graphical method proposed by Cate and Nelson (1971). The content of Zinc in the 3rd leaf lamina was found to be 21 mg kg-1. Foliar spray @ 0.75% Zn during the crop growth is recommended on identifying zinc deficiency to the crop. Zinc is an essential element for plant growth and metabolism, and exists in soil in different fractions such as Ws+Ex, OB, MnO, AmFeO, Cry FeO, and Res and all these forms are existed in a dynamic equilibrium. So the amount and rate of transformation of these forms determine the size of the labile pool of Zinc. The different fractions of Zn was also studied for the surface (0-15 cm) and subsurface soil (15-30 cm). The percentage share of different fractions in the surface soil to the total Zn was as follows i.e, Ws+exch.Zn (0.53-3.99%), 0B-Zn(2.15-3.34%), MnO-Zn (0.21-0.92%), Am. FeO-Zn (17.75-35.30%) and Cry-Fe-O Zn (30.40-59.32%) and RS-Zn (16.62-36.91%).

A path coefficient analysis was also carried out with the different fractions of Zinc on the yield of fodder maize and the results revealed that direct effect of water soluble + exchangeable fraction soil Zn on the yield of fodder maize.