Si pierdo el abono, tengo que comprar otro en la taquilla de la estación.

Yes, abono can mean fertilizer in other contexts, but here it means a travel pass, season ticket, or transport pass.

In Spain, abono is very commonly used for things like:

• abono de transporte = travel pass
• abono mensual = monthly pass

So in this sentence, el abono is the pass you use for transport, not fertilizer.

Because perder is a stem-changing verb in the present tense.

The e in the stem changes to ie in most present-tense forms:

• yo pierdo
• tú pierdes
• él/ella pierde
• nosotros perdemos
• vosotros perdéis
• ellos pierden

So pierdo is the correct yo form.

This is a very common pattern in Spanish, similar to:

• tener → tengo
• querer → quiero
• pensar → pienso

Because after si for a real or possible condition, Spanish normally uses the present tense, not the future.

So Spanish says:

• Si pierdo el abono...

not:

• Si perderé el abono... ❌

This structure is used for things that are possible in the future:

• Si llueve, no salgo.
• Si tengo tiempo, te llamo.

Even though English often uses present here too (If I lose...), learners sometimes expect a future tense because the meaning refers to the future. Spanish does not do that after si in this kind of sentence.

Both are possible, but they are not exactly the same.

• Si pierdo el abono, tengo que comprar otro
  = If I lose my pass, I have to buy another one.
  This sounds like a general rule or what normally happens.

• Si pierdo el abono, tendré que comprar otro
  = If I lose my pass, I’ll have to buy another one.
  This sounds more like a specific future consequence.

So the original sentence feels a bit more like: that’s what one has to do in that situation.

Yes, but the meaning changes slightly.

• tengo que comprar otro = I have to buy another one
  Very common, neutral, and natural.

• debo comprar otro = I should / I must buy another one
  This can sound a bit more formal, and sometimes it suggests duty rather than practical necessity.

• hay que comprar otro = you have to / one has to buy another one
  This is impersonal. It does not focus on I, but on what people generally have to do.

So tengo que is the best choice here because the sentence is about what I have to do.

Because in Spanish, otro usually does not take un when it means another.

So you say:

• comprar otro = buy another one

not:

• comprar un otro ❌

Also, otro is masculine singular because it replaces abono, which is masculine:

• el abono → otro

If the noun were feminine, you would use otra:

• la tarjeta → otra

It could. Both are correct:

• comprar otro
• comprar otro abono

Spanish often leaves out the noun when it is already obvious from context. Since abono was just mentioned, otro clearly means another pass.

This is very common in Spanish:

• Quiero un café. — Yo también quiero uno.
• Perdí el abono y tuve que comprar otro.

In this sentence, taquilla means the ticket office, ticket window, or ticket booth at the station.

In Spain, taquilla is a very normal word in transport and event contexts:

• comprar un billete en la taquilla
• la taquilla de la estación

Be aware that taquilla can have other meanings in other contexts, but here it clearly means the place where you buy tickets or passes.

Because en is used here to show the place where you buy it:

• comprar otro en la taquilla = buy another one at the ticket office

If you used a, that would usually suggest movement to the place, often with a verb like ir:

• Voy a la taquilla = I’m going to the ticket office

So:

• comprar en la taquilla = buy at the ticket office
• ir a la taquilla = go to the ticket office

De la estación means of the station or more naturally in English, at the station / the station’s.

It tells you which ticket office:

• la taquilla = the ticket office
• la taquilla de la estación = the station ticket office

Without de la estación, the sentence would still make sense, but it would be less specific.

Yes, if the context already makes it clear what lo refers to.

So these are both possible:

• Si pierdo el abono, tengo que comprar otro...
• Si lo pierdo, tengo que comprar otro...

The full noun el abono is more explicit and clearer if you are introducing the topic.
Using lo sounds more natural once the pass has already been mentioned in the conversation.

Yes, especially because of words like abono and taquilla, which are very natural in Spain.

A learner should know that vocabulary for transport can vary across the Spanish-speaking world. In Spain:

• abono = transport pass
• taquilla = ticket office/window

So this sentence sounds very natural for Spanish from Spain, especially in a train or metro context.