Information on the following questions is needed before we can attempt to answer what could be expected.

Were the crops grown under the conservation and conventional tillage system grown on a fixed plot for 4 continuous years? What type of fertilizers were used and the amount? What was the method of application? Soil type? What was the type of conservation tillage: the intensity of field disturbance that was done?

Dear Desouza

Greetings

Experiment was carried out under rice- maize system having tillage with two levels i.e conventional tillage:  one  plowing by cultivator and two harrowing  for maize planting and rice residue (3.5 Mt/ha)  35cm anchored incorporated into the soil and for conservation tillage the same amount of residue was left anchored . Whereas, in rice under conventional tillage; maize stovers (3.5 Mt/ha) was incorporated in the field  and rice was transplanted after having  two plowings followed by  puddling. Dry direct seeding of rice  in no tilled field was  done in conservation tillage . Furrows were made for no tilled maize and direct seeded rice and fertilizers were placed at soil depth of 3 cm for rice and5 cm for maize and then  covered by soil. Maize planting was done by jab planter  and rice transplanted manually. Maize was fertilized with 120:60:40 Kg  and rice with 130:50:30 kg NP2O5K2O kg/ha. Urea, DAP and MoP were the sources of N,P and K nutrients. The soil was sandy loam in texture with acidic (pH: 5.5 to 6.0) in nature. Treatments were deployed in the fixed plot.

I hope, it may be helpful to describe the situation. Looking forward eagerly.

I agree with my colleague DeSouza, relatively to local conditions of soil, cations exchange capacity of the soil, pluviometric regime  and so on. But you describe a sandy loam soil . I would dare to say that most likely the exceeding fertilizers trough washing would reach the underground water and in the open surface the rivers.How many mm of rains/ month you have in the planting season? If it is an experiment you can mark the water with isotopes to follow its trail. There are many articles about this subject available. I hope to have shed some light in the discussion.

Dear Samuel

During maize planting winter season (Nov to May), rainfall was 169 mm only and in the summer season rice (June to Nov) it was 2429 mm. Could you please suggest me the related articles.Looking forward eagerly. 

Dear Tika

Here are some suggestions of articles.

Most of them are in portuguese :

Look for them in Google scholar searching for the key words.

Tracers: the use of chemical agents for hydrological, environmental, petrochemical and biological studies

  http://www.scielo.br/scielo.php?pid=S0100-40422009000600042&script=sci_arttext

In hydrologic and hydrogeological studies, environmental isotopes have been used as a tool to identify provenience, quantify recharge and establish aquifer age. The aim of this work is to present a historic retrospective of the use of this technique in Brazil, focusing on study cases in Northeastern, Amazon and Paraná Basin regions. In addition, some comments on the main advances of this technique on a world basis, in contrast with the restrict use in Brazil help to promote a discussion on the perspectives and unfolding of this use at national level.

Key words: Environmental isotopes; hydrogeology; Brazil. 

http://ppegeo.igc.usp.br/scielo.php?pid=S0101-97592002000100003&script=sci_arttext&tlng=pt

Study of Water Flux Dynamics in the Jacuipe River

Basin Using Environmental Tracers

ABSTRACT

This research aims at the study of water flux and

interaction of surface water, ground water and meteoric

water in the Jacuípe river basin, a 12,163 km2 area representative

of the semiarid region in State of Bahia, using

environmental tracers. The results show the potential of

environmental tracers to understand the hydrologic cycle in

the study area which has insufficient hydrologic measured

data. The runoff in the Jacuípe river basin shows a trend of

heavy isotope enrichment downstream with a maximum

value in São José do Jacuípe reservoir, which reflects the

evaporation effect over the river basin and the interference

of stream exploitation. The results shows the contribution of

meteoric waters to runoff and reservoir supply when heavy

rainfall occurs, but in the dry season the runoff is mainly

from groundwater contributions and water supply in reservoirs.

Key-words:Flux dynamics, semi-arid, environmental tracers.

http://www.abrh.org.br/sgcv3/UserFiles/Revistas/08020cd85a20ab193fd78b9f487b6563_d28938f0ae84db9f1e63637bbb580606.pdf#page=29

Dear Samuel 

Greetings from Nepal

Many thanks indeed. Hope for your help in future too.

Best

Dear Tika,

Please find below an article about N transformation under mulch decomposition. Although this experiment was in controlled conditions but you can have an idea about different factors affecting N transformation..... in the presence of crop, it will further change the scenario.

Best of luck

https://www.researchgate.net/publication/275970506_Rain_regime_and_soil_type_affect_the_C_and_N_dynamics_in_soil_columns_that_are_covered_with_mixed-species_mulches

Article Rain regime and soil type affect the C and N dynamics in soi...

Dear Tika,

Please find below an article about N transformation under mulch decomposition. Although this experiment was in controlled conditions but you can have an idea about different factors affecting N transformation..... in the presence of crop, it will further change the scenario.

Best of luck

https://www.researchgate.net/publication/275970506_Rain_regime_and_soil_type_affect_the_C_and_N_dynamics_in_soil_columns_that_are_covered_with_mixed-species_mulches

Article Rain regime and soil type affect the C and N dynamics in soi...

This is interesting question. But, like others I have some queries here regarding  the forms of NPK applied, frequency of  application and practices included in the conservation tillage systems. The cropping system is cereal-cereal, without any leguminous break crop for four years.

Normally, N fertilizer is budgeted every year for a particular crop based on the fertilization practice followed, as N is a very mobile element in the soil and its use efficiency is low as reported by several researchers. But the soil test before planting is advisable to include the soil N credit in the fertilizer recommendation. With repeated application, there may be a build-up of P in the soil based on the amount applied, the type of P fertilizer and soil pH.  Potassium is found in the soil as exchangeable cation, so it may exist on soil exchange sites or it may be replaced by other exchangeable cation. In fact, soil test P and K calibration is very important to refine the PK recommendations based on soil test values.     

Dear Gatachew

Greetings

Thanks for your findings and here are the points of your queries?

1. Sources of Nutrients:

N: DAP (18:46:0 NPK) and Urea: Urea top dressed three times for maize at V5 ,V12 and VT stages) and two times for rice at  tillering stage and booting stage

P: DAP as a basal dose in furrows for both the crops

K: MOP (60% K2O) as a basal dose in furrows for both the crops (No till Maize and direct seeded rice and for transplanted rice DAP and MOP after puddling and just before paddy transplanting).

2. No legumes were introduced in the system due to the limited adjustment time in the system.

3. Soil test: yes, benchmark soil status was: pH:6.1, SOM: 2.95, N%:0.147. Available P2O5: 56.34 kg/ha and K2O: 94.87 kg/ha.

The discussion was really interesting