Usamos el riego por goteo a falta de manguera.

In this sentence, a falta de means for lack of, in the absence of, or since we don’t have.

So a falta de manguera means something like:

• for lack of a hose
• since there’s no hose
• because we don’t have a hose available

It is a fixed expression and is quite common in Spanish.

Examples:

• A falta de pan, buenas son tortas. = If there’s no bread, something else will do.
• A falta de tiempo, lo haremos mañana. = Since we don’t have time, we’ll do it tomorrow.

Spanish often leaves out subject pronouns when the verb ending already shows who the subject is.

• usamos = we use

Because -amos clearly marks we in the present tense, nosotros is usually unnecessary.

You would only add nosotros for emphasis, contrast, or clarity:

• Nosotros usamos el riego por goteo, ellos no. = We use drip irrigation, they don’t.

Spanish often uses the definite article where English may not.

Here, el riego por goteo refers to the irrigation method as a known or identifiable system: drip irrigation.

This is very normal in Spanish:

• Me gusta el café. = I like coffee.
• Estudia la biología. = He/She studies biology.

So el riego por goteo is just the standard way to say drip irrigation.

Riego means irrigation or watering, and por goteo literally means by dripping or through drops.

So:

• riego = irrigation/watering
• goteo = dripping, drip
• riego por goteo = drip irrigation

The por here expresses the method or means: irrigation by dripping.

Because por here expresses the way something is done.

• riego por goteo = irrigation by means of dripping
• enviar por correo = send by mail
• pagar por transferencia = pay by bank transfer

With de, the meaning would be different or unnatural here. Por goteo is the fixed, normal expression.

Because a falta de is commonly followed by a noun without an article when you mean in the absence of any / a needed thing.

So:

• a falta de manguera = for lack of a hose
• a falta de dinero = for lack of money
• a falta de tiempo = for lack of time

If you said a falta de la manguera, it would sound more like you are talking about a specific hose already known in the conversation:

• A falta de la manguera del jardín... = since the garden hose is missing / unavailable...

Not exactly, though they can be similar.

• sin manguera = without a hose
• a falta de manguera = for lack of a hose / since there is no hose available

Sin simply states absence.
A falta de often suggests because something needed is unavailable, we use an alternative.

So in this sentence, a falta de fits well because it implies: We use drip irrigation because we don’t have a hose.

Yes, it is understandable and natural, but a falta de can sound slightly more formal, written, or matter-of-fact than everyday speech.

In very casual spoken Spanish, people might say:

• Como no tenemos manguera, usamos riego por goteo.
• Sin manguera, usamos riego por goteo.
• Usamos riego por goteo porque no tenemos manguera.

So the original sentence is fine, but it has a slightly more formal or concise tone.

Yes, in isolation, usamos can be either:

• present: we use
• preterite: we used

Only context tells you which one it is.

In this sentence, the most likely reading is present:

• Usamos el riego por goteo a falta de manguera. = We use drip irrigation for lack of a hose.

If the context were about a finished past situation, it could mean:

• We used drip irrigation because we didn’t have a hose.

Yes. Spanish allows some flexibility in word order.

These versions are possible:

• A falta de manguera, usamos el riego por goteo.
• Usamos, a falta de manguera, el riego por goteo.
  This one is more marked and less neutral.

The most neutral versions are:

• Usamos el riego por goteo a falta de manguera.
• A falta de manguera, usamos el riego por goteo.

Putting a falta de manguera first gives slightly more emphasis to the reason or circumstance.

Usually manguera means hose or tube, and context tells you what kind.

In this sentence, it most naturally means a watering hose / garden hose.

Examples:

• manguera de jardín = garden hose
• manguera de incendio = fire hose
• manguera can also mean a flexible tube or hose in other contexts

So here, learners should understand it as hose, probably for watering.

Not if you want the same meaning.

• manguera = hose
• regadera can mean watering can in Spain, and in many places it can also mean shower head or sprinkler, depending on context and region

So replacing manguera with regadera would change the meaning.

It works like an adverbial expression giving the circumstance/reason for the action.

Main clause:

• Usamos el riego por goteo = We use drip irrigation

Adverbial expression:

• a falta de manguera = for lack of a hose / since there is no hose

So it answers something like:

• Under what circumstances?
• Why?
• Because of what lack?

Yes. Riego can refer both to:

• watering
• irrigation

In agricultural or gardening contexts, it often means irrigation.
So riego por goteo can be understood as:

• drip irrigation
• drip watering

In English, drip irrigation is usually the most standard translation.

Yes, it can be possible, but it sounds a bit less complete or a bit more technical depending on context.

Compare:

• Usamos el riego por goteo. = We use drip irrigation.
• Usamos riego por goteo. = We use drip irrigation / we use drip irrigation methods.

With the article, it sounds more like referring to the system or method as a known thing. Without it, it can sound a bit more like talking about a type of irrigation in a general, practical way.

Both can occur, but el riego por goteo is very natural and standard.